CA1041237A - Electronic system for automatically tuning to a selected television channel - Google Patents
Electronic system for automatically tuning to a selected television channelInfo
- Publication number
- CA1041237A CA1041237A CA228,478A CA228478A CA1041237A CA 1041237 A CA1041237 A CA 1041237A CA 228478 A CA228478 A CA 228478A CA 1041237 A CA1041237 A CA 1041237A
- Authority
- CA
- Canada
- Prior art keywords
- frequency
- signal
- oscillator
- signals
- circuits
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03J—TUNING RESONANT CIRCUITS; SELECTING RESONANT CIRCUITS
- H03J7/00—Automatic frequency control; Automatic scanning over a band of frequencies
- H03J7/02—Automatic frequency control
- H03J7/04—Automatic frequency control where the frequency control is accomplished by varying the electrical characteristics of a non-mechanically adjustable element or where the nature of the frequency controlling element is not significant
- H03J7/06—Automatic frequency control where the frequency control is accomplished by varying the electrical characteristics of a non-mechanically adjustable element or where the nature of the frequency controlling element is not significant using counters or frequency dividers
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03J—TUNING RESONANT CIRCUITS; SELECTING RESONANT CIRCUITS
- H03J5/00—Discontinuous tuning; Selecting predetermined frequencies; Selecting frequency bands with or without continuous tuning in one or more of the bands, e.g. push-button tuning, turret tuner
- H03J5/02—Discontinuous tuning; Selecting predetermined frequencies; Selecting frequency bands with or without continuous tuning in one or more of the bands, e.g. push-button tuning, turret tuner with variable tuning element having a number of predetermined settings and adjustable to a desired one of these settings
- H03J5/0245—Discontinuous tuning using an electrical variable impedance element, e.g. a voltage variable reactive diode, in which no corresponding analogue value either exists or is preset, i.e. the tuning information is only available in a digital form
Abstract
ELECTRONIC SYSTEM FOR
AUTOMATICALLY TUNING TO
A SELECTED TELEVISION CHANNEL
ABSTRACT
An all electronic tuning system is described for establishing a frequency of a local oscillator in a television receiver. When a channel selection is made, a number representing the desired channel is entered in a memory circuit. A first plurality of frequencies is generated in response to a channel selection, and a VCO employed as a local oscillator is caused to increase in frequency. When the VCO frequency differs from the first plurality of frequencies by a predetermined amount, a second plurality of frequencies is generated.
Each frequency generated in said second plurality of frequencies is compared with said VCO frequency. When a predetermined difference exists between said VCO frequency and said second plurality of fre-quencies, a count is recorded. When the recorded count is equivalent to the number obtained in the memory circuit, the VCO tuning is inhi-bited and the VCO frequency is stabilized until a subsequent channel selection is made.
AUTOMATICALLY TUNING TO
A SELECTED TELEVISION CHANNEL
ABSTRACT
An all electronic tuning system is described for establishing a frequency of a local oscillator in a television receiver. When a channel selection is made, a number representing the desired channel is entered in a memory circuit. A first plurality of frequencies is generated in response to a channel selection, and a VCO employed as a local oscillator is caused to increase in frequency. When the VCO frequency differs from the first plurality of frequencies by a predetermined amount, a second plurality of frequencies is generated.
Each frequency generated in said second plurality of frequencies is compared with said VCO frequency. When a predetermined difference exists between said VCO frequency and said second plurality of fre-quencies, a count is recorded. When the recorded count is equivalent to the number obtained in the memory circuit, the VCO tuning is inhi-bited and the VCO frequency is stabilized until a subsequent channel selection is made.
Description
BACKGROUND OF TIIE INVENTION
Field of the Invention This invention relates generally to the electronic tuning of a signal-receiving unit to a selected frequency and more particularly to apparatus for the automatic tuning of a television receiver to the selected channel.
Description of the Prior Art 'The tuning system of television receiver units, according to the prior art, provides for a received broadcast signal and an output signal rom a local oscillator to be applied to a heterodyne conversion transducer.
The output signal of the conversion transducer is applied to an au*omatic frequency control circuit, including a discriminator, which in turn controls the local oscillator. The output signal of the transducer is-also applied to intermediate frequency apparatus tuned to a difference .. . .
or beat frequency between the received signal'and the local oscillator frequency. The discriminator characteristics are chosen so that the local oscillator signal is maintained at a frequency to provide optimum ; performance of the intermediate frequency apparatus and subsequent demodula-tion apparatus of the television receiver. There is a local oscillator frequency which provides for the demodulation of each television channel.
It is known in the prior art to provide mechanical apparatus for' providing a coarse frequency adjustment for the local oscillator. The AFC circuit provides the vernier control of the local oscillator frequency.
It would be desirable to replace the mechanical apparatus with electronic apparatus to reduce maintenance problems associated with mechanical apparatus.
In the prior art, the received broadcast signal is used in conjunction with the local oscillator frequency in an automatic frequency tuning circuit. Original'ly, the received broadcast signal was utilized in ' 30 order to minimize changes m the frequency of the output signal of the local oscillator. However, an internal reference frequency can be employed in the AFC circuit without compromising the channel reception by the television receiver. 2 It is a desirable feature of a television tuning system to provide that the entry of a channel number in the television receiver results in the entered channel being demodulated and the audio/visual information being available. It is also a desirable feature of a television system to tune electronically to a desired channel, decreasing the maintenance problems as well as expediting production of the channel information ,after entry of the selected channel designation in the system.
It is therefore an object of the present invention to provide an improved system for tuning to a preselected frequency.
It is another object of the present invention to provide an improved television receiver.
It is yet another object of the present invention to provide an electronic system for tuning to a selected television channel.
It is a particular object of the present invention to provide an electronic automatic frequency tuning circuit for tuning to a preselected 'frequency in which a local oscillation signal and a reference generator signal are combined to stabilize the oscillator signal :Erequency.
, It is another particular objec~ oE the present invention to provide an electronic automatic frequency tuning circuit including a local oscilla-20 tor capable of electronically sweeping the frequency of the oscillator through a frequency region.
, ' It is yet another particular object of the present invention to provide a means'for halting the frequency of a local oscillator signal .~, .
frequency at a,selectbd value.
It is a still more particular object of the present invention to identify a selected television channel by counting the number of beat frequency signals resulting from a combining of a variable local oscillator and a set o harmonic frequency signals.
It is a still further object of the present invention to provide 30 ~ an electronic automatic frequency tuning circuit with a reference signal generator producing a comb of harmonic frequency signals, the beat frequency signals occurring between varying local oscillator signal and the generator .
.23~ 4 signals identifyin~ a preselected local oscillator signal, and the combined signals of the local oscillator signal and a selected harmonic frequency `of the reference generator used to stabilize the local oscillator signal.
It is a further object of the present inventlon to provide an electronic automatic frequency tuning circuit capable of tuning to every available commercial television channel.
.
SUMMARY OF THE INVENTION
.
The aforementioned and other objects are accomplished, according to the present invention, by an automatic frequency tuning circuit including a local oscillator with a controllable frequency output signal, apparatus for continuously varying the frequency of the oscillator output signal, and apparatus for combining the local oscillator output signal with a signal from a reference signal generator. The combined signals are used to identify a selected frequency of the local oscillator and suspend the changing of the frequency of the local oscillator signal. The combined signals are also used in conjunction with a discriminator circuit to stabilize the frequency of the local oscillator signal once the selected frequency is attained.
Upon entry o~ a channel designation into control apparatus of the automatic frequency tuning circuit, the channel designation causes the binary encoded channel designation to be entered in storage circuits _ and a related initial value to be entered in counting circuits of control apparatus. After entry of the initial values in the counting circuits, ; the local oscillator output signal frequency is continuously increased from a predetermined initial frequency. The signal from the reference generator, comprised of a comb of 6 MHz harmonic frequency signal components, : , .
is applied, along with the output signal of the local oscillator to a heterodyne conversion transducer. The 1 MHz beat frequency signals from the transducér are transmitted by a tuned circuit and are counted by the counting circuits of the control apparatus. Television channelsg excluding channel 5 and channel 6, have frequencies 1 MHz removed : `
appropriate 6 MHz harmonic frequencies. The local oscillator will provide the appropriate local oscillator frequency when the related number of counts has been identified by the control apparatus.
Thereaf~er, the output of the tuned circuit, applied to the dis-criminator, stabilizes the frequency of the local oscillator signal to pro-vide optimum performance of the receiver apparatus.
Chanel 5 and channel 6 can be tuned by separate apparatus.
Thus, according to the present invention, there is provided an electronic system for tuning a receiver to a selected television channel comprising: a voltage controlled oscillator; a voltage signal generator for sweeping and holding the frequency of said oscillator; a harmonic comb frequency generator for generating a first plurality of signals at 24 MHZ
frequency intervals, and a second plurality of signals at 6 MHZ frequency intervals, said first plurality of signals being selected in response to a channel selection, said second plurality of signals being generated by a first actuating signal; a mixing circuit for heterodyning the output signal of said oscillator with the output signal of said harmonic comb frequency generator; a tuned amplifier connected to said mixing circuit for transmit-ting beat frequency signals of a predetermined frequency in the output signal of said mixing circuit; an envelope detector connected to said tuned amplifier for converting said beat frequency signals to pulses, said envelope detector providing said first actuating signal to said haImonic comb frequency generator in response to a first beat frequency signal; count-ing circuits connected to said envelope detector for counting said beat frequency signal pulses; memory circuits for storing an entry number related to said selected television channel; compare circuits for comparing said beat frequency pulse count in said counting circuits with said entry number in said memory circuits and applying a second actuating signal to said voltage signal generator for stopping frequency sweeping of said oscillator when a pre-established relationship between said entry number and said pulse count exists; and a discriminator continuously coupled between said tuned amplifier and said signal generator and cooperative therewith for stabili7.ing # ~
s~
said oscillator frequency. -The invention will now be described in greater detail with reference to the accompanying drawings, in which:
Figure 1 is a block diagram of the principal functional areas of the automatic frequency tuning circuit according to the present invention;
Figure 2 is a schematic block diagram of the apparatus comprising the preferred embodiment of the invention along with related apparatus; and Figure 3 displays idealized waveforms appearing at various loca-tions of the preferred embodiment in order to illustrate operation.
Referring now to Figure 1, a block diagram of the principal areas of apparatus according to the present invention are shown. Reference signal generator 11 produces, in the preferred embodiment, a series of harmonic frequencies which are applied to heterodyne converter transducer l~. Con-currently, oscillator control circuit 13 provides a signal to controllable ,:
frequency local oscillator 12 which controls the frequency of the output signal of the local oscillator 12. The signal of local oscillator 12 is applied to transducer 14 and combined with the signal from the reference signal generator 11.
..
An output signal of transducer 14 is then applied to tuned amplifier 15. Amplifi~r 15 is tuned to a beat or difference frequency resulting :
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from the combination of the local oscillator frequency signal and the set of harmonic signals of the rèference signal generator. The output signal of tuned amplifier 15 is applied to envelope detector 16 and to discriminator 18.
A beat frequency signal will be transmitted to the output terminal of the tuned amplifier 15 when the frequency of the local oscillator signal and one of the harmonic frequency components of generator 11 differ by the frequency to which amplifier 15 is tuned. The beat frequency signal lS applied to an envelope detector 16. Detector 16 produces a pulse upon the occurrence of the beat frequency and applies this pulse to count and compare circuits 17.
Count and compare circuits 17 contain circuits for counting the number of beat frequencysignals which are applied to the output terminal of amplifier 15 and for comparing this number with a number stored in a memory portion of circuits 17. The contents of the memory portions of circuits 17 are entered by means of frequency select apparatus 19 which also provides for presetting of quantities in certain count circuits.
Upon a determination that the beat frequency signal count corresponds to a number entered in circuits 17 by the frequency select apparatus ~-20 19, the signal applied to oscillator control clrcuit 13 is removed resulting ~ ln suspension of the increase of frequency of the oscillator output signal.
~ Upon activation of apparatus 19, a signal from count and compare circuits .~ i .
17 causes the oscillator control circuit13 to provide an output signal from local oscillator 12 of increasing frequency. Concurrently, the output signal from discriminator 18, applied to circuit 13, is used to control the frequency of the output signal from the local oscillator 12.
The discriminator 18 provides a frequency response to the output signal of tuned amplifier 15 which permits the network loop comprised of discriminator, oscillator control circuit 13, controllable frequency 30 local oscillator 12, transducer 14, and amplifier 15 to "lock" on the beat frequency signal result mg from the cnmbination of the local oscillator .
signal and the generator harmonic signal component producing last count of circuit 17. The operation of this type of automatic frequency control circuit will be apparent to those skilled in the art.
Referring next to Figure 2, the preferred embodiment of the invention in a television receiver environment is shown. An antenna 51 receives televislon broadcast signals and applies these received signals to apparatus of,a television receiver. However, antenna 51 could be replaced by a cable television terminal or other apparatus for applying signals encoded at video channel frequencies to the television receiver unit.
; 10 The television receiver input signal is applied to a radio frequency amplifier 52, and the output signal of amplifier 52 is applied to heterodyne :
converter transducer 53. The radio frequency signal is "mixed" in transducer 53 wlth the local oscillator signal generated by a voltage controlled oscillator 40. The output signal of transducer 53 is applied to an ampllfier 54 ~typically tuned to 45.75 M~lz intermediate f~equency), , and the output signal of amplifier 54 is applied to demodulator and audio/visual output apparatus 55.
In order to select a specified frequency or channel, the difference between the frequency of the selected channel and the voltage controlled osclllator 40 must be equal to theintermediate frequency to which amplifier 54 lS tuned. Therefore, an appropriate output signal of the voltage , - controlled osc,illator 40 is necessary to select a channel.
- An outpùt signal of voltage controlled oscillator 40 is applied , to heterodyne conversion transducer 41. The signal from a reference oscillator 21 is applied to a harmonic comb frequency generator 22.
, Generator 22 produces a comb of equally spaced frequency signal components (i.e. in the frequency domain), the spacing being a harmonic of the ~ output signal of oscillator 21. The output signal from harmonic frequency ,, ~p~ comb signal generator 22 is also applied to transducer 41. A first and ~lip - ~'lop 3Q ~ a second output terminal of~ b-t~}-32 are coupled to comb signal ` generator 22.
The output signal from transducer 41 is applied to an intermediate frequency amplifier 42, tuned to l MHz. The output signal of amplifier .... .
.,, ~
_ 8 42 lS applied to envelope detector 45 and to discriminator 44. The .
output signal of discriminator 44 is applied to inverting/noninverting ampliier 58. The output signal of amplifier 58 is applied to one input position of a two posi~ion switch 57.
The enrelope detector 45 produces a pulse output signal each time a 1 MHz beat -frequency signal is applied to the output terminal of amplifier 42. The pulse signal is applied to counting circuits 23 and to a second B ~,`p ~op input terminal of logic gutc 32. Counting circuits 23 count the pulses produce`by envelope detector 45.
The selection of a frequency is performed by means of channel selector 27. This selection may be perform~d manually, for example by keyboard entry, or with assistance of-a remote entry device 29. The channel selector apparatus 27 is coupled to code converter 26, to monostable multivibrator 30, and to video segment generator 28. The code converter 26 is coupled to memory circuits 25 and both memory circuits 25 and count-ing circuits 23 are coupled to compare circuit 24. Compare circuit 24 is coupled to control voltage circuits 43.
Monostable multivibrator 30 is coupled to a first input terminal of ~lip~fl~p 32, to counting circuit reset 31 and to control voltage : 20 circuits 43.
The output signal from amplifier 54 is applied to discriminator - . 34, and the output signal from disc.riminator 34 is applied to a second mput terminal of the switch 57.
Channel S and channel 6 apparatus 33 is coupled to channel selector 27 and to control voltage circuits 43. Control voltage circuits 43 are coupled to voltage controlled oscillator 40.
Referring next to Figure 3, idealized output signals at several locations of Figure 2 are shown. In Figure 3~a) the output signal of the monostable multivibrator 30 is a positive value between To and Tl.
In Figure 3(b~ a reset voltage signal, supplied by control voltage CiTCUits 43 to the voltage controlled oscillator, attains an equilibrium value during an interval beginning at To~ begins increasing at Tl, and is 37 ; 9 maintained at an equilibrium value after T3. Figure 3(c) shows the output of the envelope detector signal. Pulses begin at T2 and continue until T3 is reached. Figure 3(d) shows the output voltage of a logic /P
signal applied by a first terminal-~g~c g~tc 32 to signal generator 22. At time ToJ the logic signal applied to signal generator 22 becomes a zero'value and at time T2, the logic signal becomes a positive value. The'presence of a positive signal provides for the presence of 6 MHz harmonic comb frequency components. Figure 3~e) shows the p~ Op logic signal applied by g~e 32 to generator 22. The logic signal becomes a positive value at time To and becomes a zero logic signal at time T2. The presence of this posi~ive signal provides for the presence of 24 MHz comb frequency signal components from the reference signal generator. In figure 3(f), the control signal, applied by the compare circuits 24 to,the control voltage circuits 43 is a positive value beginning ' at TOand becomes a zero value at time T3.
~, . .
0 eration of the Preferred Embodiment P
I The operation bf the preferred embodiment can be understood by ¦ consideration of Figure 2 along with Figure 3. Upon selection of a , television channel ~i.e. corresponding to a selected requency of the output signal o~ the voltage controlled oscillator) by entering a number ~ in-channel selector 27 by means of the remote entry device 29 or otherwise, .. .
, a signal from channel selector 27 is delivered to the monostable multi-,~' ' ' vibrator 30 causing the output signal of the multivibrator to assume a positive value at a time To. This causes a positive signal at terminal SO of logic g~t4 32 which enables the generation of a 24 ~Iz comb of harmonic frequency signal components by generator 22. The concurrent zero signal at terminalR0 disables the generation of a 6 MHz harmonic comb frequency components. Frequency generator 21 is comprised of a 24 MHz crystal oscillator in the preferred embodiment, either the 24 MHz comb frequency signal components or the 6 MHz harmonic comb frequency components comprise the output signal of the generator 22.
~' ' '',' ' ' .
,,~ ".~
Z37 lo In addition, a signal from multivibrator 30 is applied to counting circuits reset 31. The circuits 31 reset the counts stored in counting circuits 23 to an initial predetermined value. A signal from multivibrator 30 is also applied-to control voltage circuits 43. This signal causes the output voltage from circuits 43 to achieve a predetermined equilibrium value in the time interval between To and Tl and results in a predetermined initial frequency of the output signal of the-voltage controlled oscillator 40. The monostable multivibrator 30 maintains the positive output signal ~for the duratlon of time which the circuit remains in the astabIe state, ; lQ i.e. the time from Toto Tl.
The entry of a channel designation in channel selector 27 causes signals corresponding to the designated channel frequency to be applied to code converter 26. The code converter 26 changes the frequency designation from an arbitrary format ~i.e. channel number) to a related entry number.
The entry number, being related to the predetermined initial oscillator . .
output signal as well as other parameters, can bear a complicated relation-ship to the designated channel. The entry number is entered in memory circuits 25 and is compared, by means compare circuits 24, ~ith a count ; number in memory circuits of counting circuits 23. The activation of ~` 20 reset circuit 31sets the count number to a predetermined value. A
~ ~ .
lack of identity between the entry number and the count number wlll ~ ~ cause the compare circuits to apply a positive signal to control voltage ; circuits 43, which can cause the output voltage to attain a specified vaiue. However, the positive signal from the multivibrator 30 has priority and causes the predetermined value of voltage to be applied to voltage - controlled oscillator 40 as long as the positive multivibrator signal - is present.
When the multivibrator 30 returns to the stable configuration at time Tl, the signal from the compare circuits 24 causes the output signal 30 ~ applied to the voltage controlled oscillator to increase. The increasing voltage applied to the voltage controlled oscillator causes the frequency of the output signal of the voltage controlled oscillator to increase simultaneously. The oscillator output signal is mixed in transducer 41 with the 24 MHz signal from the comb frequency signal generator.
~0 . ~ .
When the frequency of the output signal of the voltage controlled oscillator reaches 1 h~lz below the first 24 h~z harmonic encountered by the increasing local oscillator signal frequency amplifier 42, tuned to 1 h~z applies the beat frequency signal resulting from the mixing of the comb signal generator and the voltage controlled oscillator to envelope detector 45. The occurrence of the beat frequency signal ' ~ causes detector 45 to apply a pulse to counting circuits 23, as well 7~/, p - ~/Op as a positive logic signal to Terminal Ri of ~ 32. The pulse applied to counting circuits 23 causes the count number in the memory of counting ~/,p~ p circuits 23 to increment by one. The pulse applied to ga~ 32 causes the SO
signal applied to signal generator 22 ~and resulting in a comb of 24 MHz harmonic frequency'components being applied to transducer 41~ to be removed and a positive signal applied to terminal Ro is applied to comb signal ' generator 22. The positive signal at terminal ROresults in a 6 ~-13 comb of harmonic frequency components being applied to transducer 41.
;' As the frequency of the voltage controlled'oscillator output signal continues to increase, the beat frequency signal occurs when the oscillator output voltage frequency and the frequency of one of the comb frequency - harmonic components differ by 1 h~z. The count number in the memory ~ 2~ circuit of counting circuits 23 are incremented with each beat frequency .;
signal pair identified by detector 45.
; When the count number in counting circuits 23 and the entry number of memory circuits 25 are the same, the positive signal applied to control ' voltage circults 43~is removed. With th~ removal of the positive signal ~i.e. at time T3 ) an automatic frequency control loop controls oscillator 40. The AFC loop is comprised of discriminator 44, ampIifier 5~, control' voltage circuits 43, voltage controlled oscillator 40, transducer 41, and amplifier 42. This apparatus maintains the voltage of the voltage controlled oscillator at the frequency dete-rmined by the frequency desig-nation entered m channel selector 27. The output signal of oscillator ~0 is mixed with the lncoming signals from antenna 51 and results in an' intermediate frequency of 45.75 hnlz for the information of the selected - 1 ~ ' . ' -237 l2 channel. The selected channel information will be applied to output apparatus 55. Amplifier 58 will provide amplified outpu~ signal of discriminator 44 with a positive or negative sign depending on which of the two beat frequency signals (i.e. 1 MHz above or below the related comb frequency harmonic component) is utilized in the AFC loop. The sign utilized by this amplifier can be determined by a signal from the code converter.
The oscillator 40 signal frequencies needed to tune the standard telèvision channels are 101 MHz to 113 ~lz in 6 MHz steps ~channels
Field of the Invention This invention relates generally to the electronic tuning of a signal-receiving unit to a selected frequency and more particularly to apparatus for the automatic tuning of a television receiver to the selected channel.
Description of the Prior Art 'The tuning system of television receiver units, according to the prior art, provides for a received broadcast signal and an output signal rom a local oscillator to be applied to a heterodyne conversion transducer.
The output signal of the conversion transducer is applied to an au*omatic frequency control circuit, including a discriminator, which in turn controls the local oscillator. The output signal of the transducer is-also applied to intermediate frequency apparatus tuned to a difference .. . .
or beat frequency between the received signal'and the local oscillator frequency. The discriminator characteristics are chosen so that the local oscillator signal is maintained at a frequency to provide optimum ; performance of the intermediate frequency apparatus and subsequent demodula-tion apparatus of the television receiver. There is a local oscillator frequency which provides for the demodulation of each television channel.
It is known in the prior art to provide mechanical apparatus for' providing a coarse frequency adjustment for the local oscillator. The AFC circuit provides the vernier control of the local oscillator frequency.
It would be desirable to replace the mechanical apparatus with electronic apparatus to reduce maintenance problems associated with mechanical apparatus.
In the prior art, the received broadcast signal is used in conjunction with the local oscillator frequency in an automatic frequency tuning circuit. Original'ly, the received broadcast signal was utilized in ' 30 order to minimize changes m the frequency of the output signal of the local oscillator. However, an internal reference frequency can be employed in the AFC circuit without compromising the channel reception by the television receiver. 2 It is a desirable feature of a television tuning system to provide that the entry of a channel number in the television receiver results in the entered channel being demodulated and the audio/visual information being available. It is also a desirable feature of a television system to tune electronically to a desired channel, decreasing the maintenance problems as well as expediting production of the channel information ,after entry of the selected channel designation in the system.
It is therefore an object of the present invention to provide an improved system for tuning to a preselected frequency.
It is another object of the present invention to provide an improved television receiver.
It is yet another object of the present invention to provide an electronic system for tuning to a selected television channel.
It is a particular object of the present invention to provide an electronic automatic frequency tuning circuit for tuning to a preselected 'frequency in which a local oscillation signal and a reference generator signal are combined to stabilize the oscillator signal :Erequency.
, It is another particular objec~ oE the present invention to provide an electronic automatic frequency tuning circuit including a local oscilla-20 tor capable of electronically sweeping the frequency of the oscillator through a frequency region.
, ' It is yet another particular object of the present invention to provide a means'for halting the frequency of a local oscillator signal .~, .
frequency at a,selectbd value.
It is a still more particular object of the present invention to identify a selected television channel by counting the number of beat frequency signals resulting from a combining of a variable local oscillator and a set o harmonic frequency signals.
It is a still further object of the present invention to provide 30 ~ an electronic automatic frequency tuning circuit with a reference signal generator producing a comb of harmonic frequency signals, the beat frequency signals occurring between varying local oscillator signal and the generator .
.23~ 4 signals identifyin~ a preselected local oscillator signal, and the combined signals of the local oscillator signal and a selected harmonic frequency `of the reference generator used to stabilize the local oscillator signal.
It is a further object of the present inventlon to provide an electronic automatic frequency tuning circuit capable of tuning to every available commercial television channel.
.
SUMMARY OF THE INVENTION
.
The aforementioned and other objects are accomplished, according to the present invention, by an automatic frequency tuning circuit including a local oscillator with a controllable frequency output signal, apparatus for continuously varying the frequency of the oscillator output signal, and apparatus for combining the local oscillator output signal with a signal from a reference signal generator. The combined signals are used to identify a selected frequency of the local oscillator and suspend the changing of the frequency of the local oscillator signal. The combined signals are also used in conjunction with a discriminator circuit to stabilize the frequency of the local oscillator signal once the selected frequency is attained.
Upon entry o~ a channel designation into control apparatus of the automatic frequency tuning circuit, the channel designation causes the binary encoded channel designation to be entered in storage circuits _ and a related initial value to be entered in counting circuits of control apparatus. After entry of the initial values in the counting circuits, ; the local oscillator output signal frequency is continuously increased from a predetermined initial frequency. The signal from the reference generator, comprised of a comb of 6 MHz harmonic frequency signal components, : , .
is applied, along with the output signal of the local oscillator to a heterodyne conversion transducer. The 1 MHz beat frequency signals from the transducér are transmitted by a tuned circuit and are counted by the counting circuits of the control apparatus. Television channelsg excluding channel 5 and channel 6, have frequencies 1 MHz removed : `
appropriate 6 MHz harmonic frequencies. The local oscillator will provide the appropriate local oscillator frequency when the related number of counts has been identified by the control apparatus.
Thereaf~er, the output of the tuned circuit, applied to the dis-criminator, stabilizes the frequency of the local oscillator signal to pro-vide optimum performance of the receiver apparatus.
Chanel 5 and channel 6 can be tuned by separate apparatus.
Thus, according to the present invention, there is provided an electronic system for tuning a receiver to a selected television channel comprising: a voltage controlled oscillator; a voltage signal generator for sweeping and holding the frequency of said oscillator; a harmonic comb frequency generator for generating a first plurality of signals at 24 MHZ
frequency intervals, and a second plurality of signals at 6 MHZ frequency intervals, said first plurality of signals being selected in response to a channel selection, said second plurality of signals being generated by a first actuating signal; a mixing circuit for heterodyning the output signal of said oscillator with the output signal of said harmonic comb frequency generator; a tuned amplifier connected to said mixing circuit for transmit-ting beat frequency signals of a predetermined frequency in the output signal of said mixing circuit; an envelope detector connected to said tuned amplifier for converting said beat frequency signals to pulses, said envelope detector providing said first actuating signal to said haImonic comb frequency generator in response to a first beat frequency signal; count-ing circuits connected to said envelope detector for counting said beat frequency signal pulses; memory circuits for storing an entry number related to said selected television channel; compare circuits for comparing said beat frequency pulse count in said counting circuits with said entry number in said memory circuits and applying a second actuating signal to said voltage signal generator for stopping frequency sweeping of said oscillator when a pre-established relationship between said entry number and said pulse count exists; and a discriminator continuously coupled between said tuned amplifier and said signal generator and cooperative therewith for stabili7.ing # ~
s~
said oscillator frequency. -The invention will now be described in greater detail with reference to the accompanying drawings, in which:
Figure 1 is a block diagram of the principal functional areas of the automatic frequency tuning circuit according to the present invention;
Figure 2 is a schematic block diagram of the apparatus comprising the preferred embodiment of the invention along with related apparatus; and Figure 3 displays idealized waveforms appearing at various loca-tions of the preferred embodiment in order to illustrate operation.
Referring now to Figure 1, a block diagram of the principal areas of apparatus according to the present invention are shown. Reference signal generator 11 produces, in the preferred embodiment, a series of harmonic frequencies which are applied to heterodyne converter transducer l~. Con-currently, oscillator control circuit 13 provides a signal to controllable ,:
frequency local oscillator 12 which controls the frequency of the output signal of the local oscillator 12. The signal of local oscillator 12 is applied to transducer 14 and combined with the signal from the reference signal generator 11.
..
An output signal of transducer 14 is then applied to tuned amplifier 15. Amplifi~r 15 is tuned to a beat or difference frequency resulting :
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from the combination of the local oscillator frequency signal and the set of harmonic signals of the rèference signal generator. The output signal of tuned amplifier 15 is applied to envelope detector 16 and to discriminator 18.
A beat frequency signal will be transmitted to the output terminal of the tuned amplifier 15 when the frequency of the local oscillator signal and one of the harmonic frequency components of generator 11 differ by the frequency to which amplifier 15 is tuned. The beat frequency signal lS applied to an envelope detector 16. Detector 16 produces a pulse upon the occurrence of the beat frequency and applies this pulse to count and compare circuits 17.
Count and compare circuits 17 contain circuits for counting the number of beat frequencysignals which are applied to the output terminal of amplifier 15 and for comparing this number with a number stored in a memory portion of circuits 17. The contents of the memory portions of circuits 17 are entered by means of frequency select apparatus 19 which also provides for presetting of quantities in certain count circuits.
Upon a determination that the beat frequency signal count corresponds to a number entered in circuits 17 by the frequency select apparatus ~-20 19, the signal applied to oscillator control clrcuit 13 is removed resulting ~ ln suspension of the increase of frequency of the oscillator output signal.
~ Upon activation of apparatus 19, a signal from count and compare circuits .~ i .
17 causes the oscillator control circuit13 to provide an output signal from local oscillator 12 of increasing frequency. Concurrently, the output signal from discriminator 18, applied to circuit 13, is used to control the frequency of the output signal from the local oscillator 12.
The discriminator 18 provides a frequency response to the output signal of tuned amplifier 15 which permits the network loop comprised of discriminator, oscillator control circuit 13, controllable frequency 30 local oscillator 12, transducer 14, and amplifier 15 to "lock" on the beat frequency signal result mg from the cnmbination of the local oscillator .
signal and the generator harmonic signal component producing last count of circuit 17. The operation of this type of automatic frequency control circuit will be apparent to those skilled in the art.
Referring next to Figure 2, the preferred embodiment of the invention in a television receiver environment is shown. An antenna 51 receives televislon broadcast signals and applies these received signals to apparatus of,a television receiver. However, antenna 51 could be replaced by a cable television terminal or other apparatus for applying signals encoded at video channel frequencies to the television receiver unit.
; 10 The television receiver input signal is applied to a radio frequency amplifier 52, and the output signal of amplifier 52 is applied to heterodyne :
converter transducer 53. The radio frequency signal is "mixed" in transducer 53 wlth the local oscillator signal generated by a voltage controlled oscillator 40. The output signal of transducer 53 is applied to an ampllfier 54 ~typically tuned to 45.75 M~lz intermediate f~equency), , and the output signal of amplifier 54 is applied to demodulator and audio/visual output apparatus 55.
In order to select a specified frequency or channel, the difference between the frequency of the selected channel and the voltage controlled osclllator 40 must be equal to theintermediate frequency to which amplifier 54 lS tuned. Therefore, an appropriate output signal of the voltage , - controlled osc,illator 40 is necessary to select a channel.
- An outpùt signal of voltage controlled oscillator 40 is applied , to heterodyne conversion transducer 41. The signal from a reference oscillator 21 is applied to a harmonic comb frequency generator 22.
, Generator 22 produces a comb of equally spaced frequency signal components (i.e. in the frequency domain), the spacing being a harmonic of the ~ output signal of oscillator 21. The output signal from harmonic frequency ,, ~p~ comb signal generator 22 is also applied to transducer 41. A first and ~lip - ~'lop 3Q ~ a second output terminal of~ b-t~}-32 are coupled to comb signal ` generator 22.
The output signal from transducer 41 is applied to an intermediate frequency amplifier 42, tuned to l MHz. The output signal of amplifier .... .
.,, ~
_ 8 42 lS applied to envelope detector 45 and to discriminator 44. The .
output signal of discriminator 44 is applied to inverting/noninverting ampliier 58. The output signal of amplifier 58 is applied to one input position of a two posi~ion switch 57.
The enrelope detector 45 produces a pulse output signal each time a 1 MHz beat -frequency signal is applied to the output terminal of amplifier 42. The pulse signal is applied to counting circuits 23 and to a second B ~,`p ~op input terminal of logic gutc 32. Counting circuits 23 count the pulses produce`by envelope detector 45.
The selection of a frequency is performed by means of channel selector 27. This selection may be perform~d manually, for example by keyboard entry, or with assistance of-a remote entry device 29. The channel selector apparatus 27 is coupled to code converter 26, to monostable multivibrator 30, and to video segment generator 28. The code converter 26 is coupled to memory circuits 25 and both memory circuits 25 and count-ing circuits 23 are coupled to compare circuit 24. Compare circuit 24 is coupled to control voltage circuits 43.
Monostable multivibrator 30 is coupled to a first input terminal of ~lip~fl~p 32, to counting circuit reset 31 and to control voltage : 20 circuits 43.
The output signal from amplifier 54 is applied to discriminator - . 34, and the output signal from disc.riminator 34 is applied to a second mput terminal of the switch 57.
Channel S and channel 6 apparatus 33 is coupled to channel selector 27 and to control voltage circuits 43. Control voltage circuits 43 are coupled to voltage controlled oscillator 40.
Referring next to Figure 3, idealized output signals at several locations of Figure 2 are shown. In Figure 3~a) the output signal of the monostable multivibrator 30 is a positive value between To and Tl.
In Figure 3(b~ a reset voltage signal, supplied by control voltage CiTCUits 43 to the voltage controlled oscillator, attains an equilibrium value during an interval beginning at To~ begins increasing at Tl, and is 37 ; 9 maintained at an equilibrium value after T3. Figure 3(c) shows the output of the envelope detector signal. Pulses begin at T2 and continue until T3 is reached. Figure 3(d) shows the output voltage of a logic /P
signal applied by a first terminal-~g~c g~tc 32 to signal generator 22. At time ToJ the logic signal applied to signal generator 22 becomes a zero'value and at time T2, the logic signal becomes a positive value. The'presence of a positive signal provides for the presence of 6 MHz harmonic comb frequency components. Figure 3~e) shows the p~ Op logic signal applied by g~e 32 to generator 22. The logic signal becomes a positive value at time To and becomes a zero logic signal at time T2. The presence of this posi~ive signal provides for the presence of 24 MHz comb frequency signal components from the reference signal generator. In figure 3(f), the control signal, applied by the compare circuits 24 to,the control voltage circuits 43 is a positive value beginning ' at TOand becomes a zero value at time T3.
~, . .
0 eration of the Preferred Embodiment P
I The operation bf the preferred embodiment can be understood by ¦ consideration of Figure 2 along with Figure 3. Upon selection of a , television channel ~i.e. corresponding to a selected requency of the output signal o~ the voltage controlled oscillator) by entering a number ~ in-channel selector 27 by means of the remote entry device 29 or otherwise, .. .
, a signal from channel selector 27 is delivered to the monostable multi-,~' ' ' vibrator 30 causing the output signal of the multivibrator to assume a positive value at a time To. This causes a positive signal at terminal SO of logic g~t4 32 which enables the generation of a 24 ~Iz comb of harmonic frequency signal components by generator 22. The concurrent zero signal at terminalR0 disables the generation of a 6 MHz harmonic comb frequency components. Frequency generator 21 is comprised of a 24 MHz crystal oscillator in the preferred embodiment, either the 24 MHz comb frequency signal components or the 6 MHz harmonic comb frequency components comprise the output signal of the generator 22.
~' ' '',' ' ' .
,,~ ".~
Z37 lo In addition, a signal from multivibrator 30 is applied to counting circuits reset 31. The circuits 31 reset the counts stored in counting circuits 23 to an initial predetermined value. A signal from multivibrator 30 is also applied-to control voltage circuits 43. This signal causes the output voltage from circuits 43 to achieve a predetermined equilibrium value in the time interval between To and Tl and results in a predetermined initial frequency of the output signal of the-voltage controlled oscillator 40. The monostable multivibrator 30 maintains the positive output signal ~for the duratlon of time which the circuit remains in the astabIe state, ; lQ i.e. the time from Toto Tl.
The entry of a channel designation in channel selector 27 causes signals corresponding to the designated channel frequency to be applied to code converter 26. The code converter 26 changes the frequency designation from an arbitrary format ~i.e. channel number) to a related entry number.
The entry number, being related to the predetermined initial oscillator . .
output signal as well as other parameters, can bear a complicated relation-ship to the designated channel. The entry number is entered in memory circuits 25 and is compared, by means compare circuits 24, ~ith a count ; number in memory circuits of counting circuits 23. The activation of ~` 20 reset circuit 31sets the count number to a predetermined value. A
~ ~ .
lack of identity between the entry number and the count number wlll ~ ~ cause the compare circuits to apply a positive signal to control voltage ; circuits 43, which can cause the output voltage to attain a specified vaiue. However, the positive signal from the multivibrator 30 has priority and causes the predetermined value of voltage to be applied to voltage - controlled oscillator 40 as long as the positive multivibrator signal - is present.
When the multivibrator 30 returns to the stable configuration at time Tl, the signal from the compare circuits 24 causes the output signal 30 ~ applied to the voltage controlled oscillator to increase. The increasing voltage applied to the voltage controlled oscillator causes the frequency of the output signal of the voltage controlled oscillator to increase simultaneously. The oscillator output signal is mixed in transducer 41 with the 24 MHz signal from the comb frequency signal generator.
~0 . ~ .
When the frequency of the output signal of the voltage controlled oscillator reaches 1 h~lz below the first 24 h~z harmonic encountered by the increasing local oscillator signal frequency amplifier 42, tuned to 1 h~z applies the beat frequency signal resulting from the mixing of the comb signal generator and the voltage controlled oscillator to envelope detector 45. The occurrence of the beat frequency signal ' ~ causes detector 45 to apply a pulse to counting circuits 23, as well 7~/, p - ~/Op as a positive logic signal to Terminal Ri of ~ 32. The pulse applied to counting circuits 23 causes the count number in the memory of counting ~/,p~ p circuits 23 to increment by one. The pulse applied to ga~ 32 causes the SO
signal applied to signal generator 22 ~and resulting in a comb of 24 MHz harmonic frequency'components being applied to transducer 41~ to be removed and a positive signal applied to terminal Ro is applied to comb signal ' generator 22. The positive signal at terminal ROresults in a 6 ~-13 comb of harmonic frequency components being applied to transducer 41.
;' As the frequency of the voltage controlled'oscillator output signal continues to increase, the beat frequency signal occurs when the oscillator output voltage frequency and the frequency of one of the comb frequency - harmonic components differ by 1 h~z. The count number in the memory ~ 2~ circuit of counting circuits 23 are incremented with each beat frequency .;
signal pair identified by detector 45.
; When the count number in counting circuits 23 and the entry number of memory circuits 25 are the same, the positive signal applied to control ' voltage circults 43~is removed. With th~ removal of the positive signal ~i.e. at time T3 ) an automatic frequency control loop controls oscillator 40. The AFC loop is comprised of discriminator 44, ampIifier 5~, control' voltage circuits 43, voltage controlled oscillator 40, transducer 41, and amplifier 42. This apparatus maintains the voltage of the voltage controlled oscillator at the frequency dete-rmined by the frequency desig-nation entered m channel selector 27. The output signal of oscillator ~0 is mixed with the lncoming signals from antenna 51 and results in an' intermediate frequency of 45.75 hnlz for the information of the selected - 1 ~ ' . ' -237 l2 channel. The selected channel information will be applied to output apparatus 55. Amplifier 58 will provide amplified outpu~ signal of discriminator 44 with a positive or negative sign depending on which of the two beat frequency signals (i.e. 1 MHz above or below the related comb frequency harmonic component) is utilized in the AFC loop. The sign utilized by this amplifier can be determined by a signal from the code converter.
The oscillator 40 signal frequencies needed to tune the standard telèvision channels are 101 MHz to 113 ~lz in 6 MHz steps ~channels
2 through 4), 221 ~lz to 257 ~z in 6 ~lz steps ~channels 7 through 13), and 517 MHz to 931 MHz in 6 MHz s~eps (channels 14 through 83).
101 MHz, 107 MHz, ~13 M~z, and 221 M~lz through 257 ~z all are 1 hlHz below 6 MHz harmonic signals (i.e. generated by the comb signal generator).
; Similarly 517 M~lz through 931 MHz are 1 h~lz above the 6 MHz harmonic signals. By enabling and operating the automatic frequency control - loop through appropriate 1 MHz beat frequency of the nearest 6 MHz harmonic frequency signal, the voltage controlled oscillator signal is stabilized at a frequency appropriate to provide demodulation of the incoming signals by the television receiver.
~The selection of the appropriate beat frequency signal from the sequence of beat frequency signals is determined by the entry number.
Code converter 26 specifies the count number which is related to each program channel. In the preferred embodiment, code converter 26 utilizes - a programmable read-only memory. By changing to a dif~erent programmable read-only memory, a variety of input devices can be utilized with the television receiver.
To enhance the flexibility of the invention, a second automatic frequency control loop comprised of heterodyne converter transducer 53, tuned amplifier 54, discriminator 34, control voltage circuits 43, and voltage controlled oscillator 40 is provided. This circuit can be placed in operat-ion by appropriate positioning of switch 57. This loop allows the effective demodulation of channels on which, as opposed to commercial broadcast channels, drift of the frequency of the information bearing channel can be a problem. ~ 2 . ~ .i . .
23~J
To accomodate channel 5 and channel 6, which do not have a convenient_ frequency relationship to 6 MHz harmonic frequencies, separate apparatus 33-can be included. For example, a potentiometer can be used to provide the appropriate voltage level at the output of control voltage circuit 43, thereby providing the desired frequency of the output signal of oscillator 40. In another embodiment, the entry of channel 5 or channel ~6 in the channel selector 27 can activate a special oscillator causing an appropriate frequency (or frequencies) to be applied to transducer 41.
10The video segment generator 28 is used in the preferred embodiment to display the channel entered in the television receiver on the display tube face.
In the preferred embodiment, a receiver operator can enter any channel designation (except 5 and 6) in the channel selector and the disclosed apparatus, starting at a predetermined initial position will sequentially cycle through consecutive channel signal frequencies until the appropriate local oscillator signal-frequency is obtained. Because `~ of the rapid time of the alectronic tuning, the cycling is not apparent and the apparatus provides the information from the selected channel ~o ~; 20 the audio/visual output apparatus without noticeable delay.
It will be apparent that the frequency of the oscillator 40 can begin between the 3rd. and 4th. harmonic of the 24 MHz comb frequency components. The counting number can then be incremented beginning with ~. .
the 1 h~z beat frequency signal below the 4th. harmonic of the 24 MHz comb frequency generator signal~. Thus the control voltage circuits output signal, during the interval To to Tl, does not reach a zero value but instead produces a voltage value causing an oscillator signal frequency lying between 73 h~z (3 x 24 h~lz + 1 h~z) and 95 MHz (4x 24 ~Iz - 1 ~z).
As will be apparent, another implementation involves the value of the output signal oscillator 40 achieving an initial frequency value between the 4th. and 5th. harmonics of the 24 h~lz harmonic frequency comb, decreasing the oscillator frequency until the beat frequency signal .
~ 1~
, .
.;Z 37 14 above the 4th harmonic of the 24 h~z comb generator signal produced a count. The frequency of the oscillator output signal is thereafter changed in the direction of increasing signal frequency. It is also possible to initiate the oscillator output fre~uency between appropriate ~n x 6 h~z + 1 MHz) and ~n~ 1~6 MHz - 1 ~z)frequencies thereby dispensing with the 24 M}lz harmonic comb, however more accurate control of the initial output signal of the control voltage circuits is required.
It will also be apparent that the initial oscillator output signal frequency can be made dependent on the channel designation. Because of the rapidity of the electronic frequency sweep, this implementation can add apparatus complexlty-without a corresponding increase in view-identifiable performance.
It will be clear to those skilled in the art that the reference oscil-lator can provide a frequency other than 24 h~z ~e.g. 12 MHz) in relative embodiments without affecting the underlying principles of operation.
The present implementation of the preferred embodiment envisions logic signal comparison between the count mlmber and the entry number.
It will be apparent that other data manipulation schemes can be utilized.
For example, code converter 2~ can enter a quantity directly into register units of counting circuits 23. Thereafter, identification of beat frequency signals increments or decreinents the register unit until a predetermined register state causes the removal of the positive signal applied to control voltage circuits 43.
The above description is included to illustrate the operation of the preferred embodiment and is not meant to limit the scope of the invention. The scope of the invention is to be limited only by the following claims. From the above discussion, many variations would yet be apparent to one skilled-in the art that would yet be encompassed by the spirit and scope of the invention.
- . ~ . .
. ~ ' ' J. ,~
~: :
'
101 MHz, 107 MHz, ~13 M~z, and 221 M~lz through 257 ~z all are 1 hlHz below 6 MHz harmonic signals (i.e. generated by the comb signal generator).
; Similarly 517 M~lz through 931 MHz are 1 h~lz above the 6 MHz harmonic signals. By enabling and operating the automatic frequency control - loop through appropriate 1 MHz beat frequency of the nearest 6 MHz harmonic frequency signal, the voltage controlled oscillator signal is stabilized at a frequency appropriate to provide demodulation of the incoming signals by the television receiver.
~The selection of the appropriate beat frequency signal from the sequence of beat frequency signals is determined by the entry number.
Code converter 26 specifies the count number which is related to each program channel. In the preferred embodiment, code converter 26 utilizes - a programmable read-only memory. By changing to a dif~erent programmable read-only memory, a variety of input devices can be utilized with the television receiver.
To enhance the flexibility of the invention, a second automatic frequency control loop comprised of heterodyne converter transducer 53, tuned amplifier 54, discriminator 34, control voltage circuits 43, and voltage controlled oscillator 40 is provided. This circuit can be placed in operat-ion by appropriate positioning of switch 57. This loop allows the effective demodulation of channels on which, as opposed to commercial broadcast channels, drift of the frequency of the information bearing channel can be a problem. ~ 2 . ~ .i . .
23~J
To accomodate channel 5 and channel 6, which do not have a convenient_ frequency relationship to 6 MHz harmonic frequencies, separate apparatus 33-can be included. For example, a potentiometer can be used to provide the appropriate voltage level at the output of control voltage circuit 43, thereby providing the desired frequency of the output signal of oscillator 40. In another embodiment, the entry of channel 5 or channel ~6 in the channel selector 27 can activate a special oscillator causing an appropriate frequency (or frequencies) to be applied to transducer 41.
10The video segment generator 28 is used in the preferred embodiment to display the channel entered in the television receiver on the display tube face.
In the preferred embodiment, a receiver operator can enter any channel designation (except 5 and 6) in the channel selector and the disclosed apparatus, starting at a predetermined initial position will sequentially cycle through consecutive channel signal frequencies until the appropriate local oscillator signal-frequency is obtained. Because `~ of the rapid time of the alectronic tuning, the cycling is not apparent and the apparatus provides the information from the selected channel ~o ~; 20 the audio/visual output apparatus without noticeable delay.
It will be apparent that the frequency of the oscillator 40 can begin between the 3rd. and 4th. harmonic of the 24 MHz comb frequency components. The counting number can then be incremented beginning with ~. .
the 1 h~z beat frequency signal below the 4th. harmonic of the 24 MHz comb frequency generator signal~. Thus the control voltage circuits output signal, during the interval To to Tl, does not reach a zero value but instead produces a voltage value causing an oscillator signal frequency lying between 73 h~z (3 x 24 h~lz + 1 h~z) and 95 MHz (4x 24 ~Iz - 1 ~z).
As will be apparent, another implementation involves the value of the output signal oscillator 40 achieving an initial frequency value between the 4th. and 5th. harmonics of the 24 h~lz harmonic frequency comb, decreasing the oscillator frequency until the beat frequency signal .
~ 1~
, .
.;Z 37 14 above the 4th harmonic of the 24 h~z comb generator signal produced a count. The frequency of the oscillator output signal is thereafter changed in the direction of increasing signal frequency. It is also possible to initiate the oscillator output fre~uency between appropriate ~n x 6 h~z + 1 MHz) and ~n~ 1~6 MHz - 1 ~z)frequencies thereby dispensing with the 24 M}lz harmonic comb, however more accurate control of the initial output signal of the control voltage circuits is required.
It will also be apparent that the initial oscillator output signal frequency can be made dependent on the channel designation. Because of the rapidity of the electronic frequency sweep, this implementation can add apparatus complexlty-without a corresponding increase in view-identifiable performance.
It will be clear to those skilled in the art that the reference oscil-lator can provide a frequency other than 24 h~z ~e.g. 12 MHz) in relative embodiments without affecting the underlying principles of operation.
The present implementation of the preferred embodiment envisions logic signal comparison between the count mlmber and the entry number.
It will be apparent that other data manipulation schemes can be utilized.
For example, code converter 2~ can enter a quantity directly into register units of counting circuits 23. Thereafter, identification of beat frequency signals increments or decreinents the register unit until a predetermined register state causes the removal of the positive signal applied to control voltage circuits 43.
The above description is included to illustrate the operation of the preferred embodiment and is not meant to limit the scope of the invention. The scope of the invention is to be limited only by the following claims. From the above discussion, many variations would yet be apparent to one skilled-in the art that would yet be encompassed by the spirit and scope of the invention.
- . ~ . .
. ~ ' ' J. ,~
~: :
'
Claims
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An electronic system for tuning a receiver to a selected television channel comprising:
(a) a voltage controlled oscillator;
(b) a voltage signal generator for sweeping and holding the frequency of said oscillator;
(c) a harmonic comb frequency generator for generating a first plur-ality of signals at 24 MHZ frequency intervals, and a second plurality of signals at 6 MHZ frequency intervals, said first plurality of signals being selected in response to a channel selection, said second plurality of signals being generated by a first actuating signal;
(d) a mixing circuit for heterodyning the output signal of said oscillator with the output signal of said harmonic comb frequency generator;
(e) a tuned amplifier connected to said mixing circuit for transmitting beat frequency signals of a predetermined frequency in the output signal of said mixing circuit;
(f) an envelope detector connected to said tuned amplifier for convert-ing said beat frequency signals to pulses, said envelope detector providing said first actuating signal to said harmonic comb frequency generator in response to a first beat frequency signal;
(g) counting circuits connected to said envelope detector for counting said beat frequency signal pulses;
(h) memory circuits for storing an entry number related to said selected television channel;
(i) compare circuits for comparing said beat frequency pulse count in said counting circuits with said entry number in said memory circuits and applying a second actuating signal to said voltage signal generator for stopping frequency sweeping of said oscillator when a pre-established relationship between said entry number and said pulse count exists; and (j) a discriminator continuously coupled between said tuned amplifier and said signal generator and cooperative therewith for stabilizing said oscillator frequency.
(a) a voltage controlled oscillator;
(b) a voltage signal generator for sweeping and holding the frequency of said oscillator;
(c) a harmonic comb frequency generator for generating a first plur-ality of signals at 24 MHZ frequency intervals, and a second plurality of signals at 6 MHZ frequency intervals, said first plurality of signals being selected in response to a channel selection, said second plurality of signals being generated by a first actuating signal;
(d) a mixing circuit for heterodyning the output signal of said oscillator with the output signal of said harmonic comb frequency generator;
(e) a tuned amplifier connected to said mixing circuit for transmitting beat frequency signals of a predetermined frequency in the output signal of said mixing circuit;
(f) an envelope detector connected to said tuned amplifier for convert-ing said beat frequency signals to pulses, said envelope detector providing said first actuating signal to said harmonic comb frequency generator in response to a first beat frequency signal;
(g) counting circuits connected to said envelope detector for counting said beat frequency signal pulses;
(h) memory circuits for storing an entry number related to said selected television channel;
(i) compare circuits for comparing said beat frequency pulse count in said counting circuits with said entry number in said memory circuits and applying a second actuating signal to said voltage signal generator for stopping frequency sweeping of said oscillator when a pre-established relationship between said entry number and said pulse count exists; and (j) a discriminator continuously coupled between said tuned amplifier and said signal generator and cooperative therewith for stabilizing said oscillator frequency.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US05/476,503 US4020419A (en) | 1974-06-05 | 1974-06-05 | Electronic system for automatically tuning to a selected television channel |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1041237A true CA1041237A (en) | 1978-10-24 |
Family
ID=23892106
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA228,478A Expired CA1041237A (en) | 1974-06-05 | 1975-06-04 | Electronic system for automatically tuning to a selected television channel |
Country Status (3)
| Country | Link |
|---|---|
| US (1) | US4020419A (en) |
| JP (1) | JPS5124814A (en) |
| CA (1) | CA1041237A (en) |
Families Citing this family (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4425578A (en) | 1981-01-12 | 1984-01-10 | A. C. Nielsen Company | Monitoring system and method utilizing signal injection for determining channel reception of video receivers |
| US4965825A (en) | 1981-11-03 | 1990-10-23 | The Personalized Mass Media Corporation | Signal processing apparatus and methods |
| US7831204B1 (en) | 1981-11-03 | 2010-11-09 | Personalized Media Communications, Llc | Signal processing apparatus and methods |
| USRE47642E1 (en) | 1981-11-03 | 2019-10-08 | Personalized Media Communications LLC | Signal processing apparatus and methods |
| US4616191A (en) * | 1983-07-05 | 1986-10-07 | Raytheon Company | Multifrequency microwave source |
| US4598422A (en) * | 1984-08-24 | 1986-07-01 | General Electric Company | Harmonic tuning system for radio receivers |
| US4723302A (en) * | 1986-08-05 | 1988-02-02 | A. C. Nielsen Company | Method and apparatus for determining channel reception of a receiver |
| US5389964A (en) * | 1992-12-30 | 1995-02-14 | Information Resources, Inc. | Broadcast channel substitution method and apparatus |
| US5404161A (en) * | 1993-07-27 | 1995-04-04 | Information Resources, Inc. | Tuned signal detector for use with a radio frequency receiver |
| US6941573B1 (en) | 1996-08-07 | 2005-09-06 | Information Resources, Inc. | Television distribution system for signal substitution |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3259851A (en) * | 1961-11-01 | 1966-07-05 | Avco Corp | Digital system for stabilizing the operation of a variable frequency oscillator |
| US3221266A (en) * | 1964-03-03 | 1965-11-30 | Hewlett Packard Co | Linear sweep frequency generator |
| US3641434A (en) * | 1968-10-10 | 1972-02-08 | Bendix Corp | Wide-band crystal-controlled transceiver with remote digital tuning |
| US3846707A (en) * | 1970-11-04 | 1974-11-05 | Matsushita Electric Co Ltd | Channel selection device |
| NL166828C (en) * | 1971-05-08 | 1981-09-15 | Matsushita Electric Ind Co Ltd | AUTOMATIC CHANNEL SELECTING DEVICE. |
| US3864636A (en) * | 1972-11-09 | 1975-02-04 | Tokyo Shibaura Electric Co | Local oscillation device for a television receiver set |
| US3857107A (en) * | 1973-06-19 | 1974-12-24 | T Hopp | Digital counter frequency control system |
| US3924192A (en) * | 1974-06-03 | 1975-12-02 | Rca Corp | Multiband random channel address crystal-lock tuning system |
-
1974
- 1974-06-05 US US05/476,503 patent/US4020419A/en not_active Expired - Lifetime
-
1975
- 1975-06-04 CA CA228,478A patent/CA1041237A/en not_active Expired
- 1975-06-05 JP JP50068086A patent/JPS5124814A/ja active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5124814A (en) | 1976-02-28 |
| US4020419A (en) | 1977-04-26 |
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