US2861186A - Signal attenuating circuit - Google Patents

Description

Nov 18, 1958 a Ross| ETAL 86 SIGNAL ATTENUATING CIRCUIT Filed Feb. 1. 1946 l LJ l -l Ln INVENTORS BRUNO ROSSI I HENRI S. SACK ALBERT C. BEER HOWARD w. BOEHMER ATTORNEY States of America as represented by the Secretary of the Navy e v 1 Application February 1, 1946, Serial No. 644,970 3 Claims. (Cl. 250-27) This invention relates to voltage attenuators and more particularly, to constant output level attenuators for use in electronic computer circuits.

There are knownjto the art electronic computer circuits for performing a number of mathematical operations, as for example, division, multiplication, squaring, and extracting square roots. The basic principle of the aforementioned computing devices involves the usecf ted States Patent attenuators having a constant output level and variable attenuation constant.

Accordingly, it is an object of this invention to provide an attenuator in which the output level is constant.

It is also an object of this invention to" provide an attenuator in which the attenuation constant is variable.

The principle of the invention will be made apparent by the following detailed discussion andthe appended drawing which is a circuit diagram of one embodiment of the invention. f

The basic principle of the invention is to permit'the input voltage to charge. a condenser during a fraction k of a time period T, and then. permit the condenser to discharge during. the remainder of the period, that is, during (1k)T.. .The. average voltage across the condenser will be a fraction ofthe input voltage, and the fraction will be directly proportional to. the fraction it during which the condenser is charged. Thus, by varying k, the attenuation constant of the attenuator may be changed.

The preferred embodiment of the invention shown in the single figure comprises a vacuum tube 10 having two triode sections, the grids of which are connected to input terminals 14 and 15 respectively. Four resistors 11, provide cathode and plate loads for each triode. These resistors are connected from the plate of each triode section to a source of positive potential and from the cathode of each triode section to ground. A second vacuum tube 13, also having two triode sections, is connected in parallel with tube 10, the plate and cathode of the first section of tube 13 being connected respectively to the plate and cathode of the first section of tube 10, and the plate and cathode of the second section of tube 13 being connected respectively to the plate and cathode of the second section of tube 10. The grids of both triode sections of tube 13 are connected to a terminal 22 to which is applied a square wave voltage having a period T, the duration of the negative portion of the square wave cycle being KT.

Two resistors 12 are connected in series between the plate of the first triode section and the cathode of the second triode section of tube 10, and the junction of these resistors is connected to one terminal of a condenser 16 and to an output terminal 20. A second pair of resistors 12 are connected in series between the plate of the second triode section and the cathode of the first triode section of tube 10, and have their junction connected to one terminal of a second condenser 17 and to a second output terminal 21. The remaining terminals of resistors 16 and 17 are connected together to ground.

The two triode sections of electron tube 10 together with load resistors 11 and resistance bridge 12 acts as a diiferential amplifier with a constant output level provided no current is drawn by the triode sections of electron tube 13. Assuming tube 13 to be non-conducting, undirectional input voltages A and A applied at input terminals 14 and 15, respectively, will establish output voltages equal to a and a across condensers 16 and 17. There will then be available at output terminals 20 and 21 a differential output (a -a which will be equal to C(A A where C is a constant whose value is dependent upon the circuit parameters, supply voltage, Q

If then tube 13 isbrought into conduction by applying a positive voltage and the characteristics of tube 10.

.positiverectangular portion of the square wave applied to terminal 22, a pair of current paths are established between the positive supply voltage of the twin triodes 10 and ground via the anode resistors 11, the twin triode sections of tube 13 and the cathode resistors 11. The

voltage at the cathodes of both sections of triode 10 is then sufiiciently positive to cut ofl these sections even in the presence of positive input signals on their control grids 14 and 15. Hence, the input signals are eflectively prevented from influencing the discharge action of the capacitors and distorting the wave form of the output signal. The discharge path of capacitor 16 is, in the case where its voltage exceeds that of capacitor .17, via the upper left-hand resistor 12, the left-hand section of twin triode 13 and the lower right-hand resistor 12.

It will be apparent that if tube--13 were controlled by having applied to its grid a square wave voltage of period T which is negative during a time kT and is positive during the remaining time (1k)T, for every period, the average differential voltage at terminals 20 and 21 will be equal to C(A -A )k. The attenuation constant of this attenuator will then be equal to Ck as defined above and can readily be varied by changing the factor k. This variation can be accomplished by varying the pulse width of the square wave input to terminal 22. It will also be apparent that in this form of the invention, the differential output need not be taken. One side of the output, for example a may be taken for such applications where a differential output is not desired. In the latter case it willbe appreciated that capacitor 16, for example, will have its discharge path via the upper left-hand resistor 12, the left section of triode 3 and cathode resistor 11 of the left-hand section of triode 10.

The description in this specification of one embodiment of the invention is for the purpose of illustrating the principles thereof. Other embodiments will suggest themselves to those skilled in the art and no attempt has been made to exhaust such possibilities. The scope and spirit of the invention are defined in the appended claims.

What is claimed is:

l. A signal attenuator comprising, in combination, first and second electron tubes, said tubes being connected in parallel, plate to plate and cathode to cathode, and having a common cathode resistor, a storage capacitor in the plate circuit of said first electron tube, means for coupling an input signal to the control grid of said first tube and means for coupling a switching signal having a period T to the control grid of said second tube, said switching signal having a negative portion during which said second electron tube is held Patented Nov. 18,1958;

nonconducting and the voltage level across said storage capacitor follows the amplitude of the input signal and a positive portion during which said second tube is held sutliciently conducting to cut oil said first electron tube by-- the blocking bias developed across said common cathode resistor and to permit said storage capacitor to discharge therethrough to a voltage level determined partially by the length of time said second electron tube is held conducting whereby the amplitude of the voltage wave produced across said storage capacitor is related to the amplitude of the input signal as the negative portion of said switching signal is related to the period T of said switching signal.

2. A signal attenuating circuit comprising, in combination, first and second electron tubes, each of said tubes having at least an anode, a control grid and a cathode, means for directly connecting the anode of said first tube to the anode of said second tube and the cathode of said first tube to the cathode of said second tube, a load resistor, said load resistor being connected to the anodes of said tubes andto a source of positive potential, a cathode resistor connected to the cathodes of said tubes and to a reference potential, a second resistor, a storage capacitor, said second resistor and storage capacitor being connected in series between the anodes of said tube and said reference potential, means for applying the signal to be attenuated to the control grid of said first tube and means for applying a switching signal to the control grid of said second tube, said switching signal having a;

negative portion which renders the second electron tube nonconducting and allows said storage capacitor to charge towards the amplitude of the signal present at the control grid of said first electron tube and a second positive portion which renders said second electron tube conducting so as to shunt said first electron tube and permit said storage capacitor to discharge through said second resistor, said second electron tube and said cathode resistor to a voltage level determined in part by the duration of this second portion of the switching signal, whereby the voltage present across said storage capacitor is an attenuated approximation of the signal presence at the control grid of said first electron tube.

3. A signal attenuating circuit comprising, in combination, first and second electron tubes, each of said tubes having at least an anode, a. control grid and a cathode, a common load resistor connected between the anodes of said tubes and a positive operating potential, a common cathode resistor connected between the cathodes of said tubes and a reference potential, at second resistor, a storage capacitor, meansfor connecting one end of said second resistor to one plate of said storage capacitor, means for connecting: the other end of said resistor to both of said anodes and the other plate of said capacitor to said reference potential, means for coupling a signal that is to be attenuated tovthe control grid of said first tube and means for coupling a switching signal having a period T to the control grid of said second tube, said switching signal having a negative rectangular portion which biases said second tube to nonconduction and thereby allows the voltage level across said storage capacitor to follow the amplitude of the signal present at References Cited in the file of this patent UNITED STATES PATENTS 1,851,090 Fetter Mar. 29, 1932 2,180,364 Norton: Nov. 21, 1939 2,242,948 Gulliksen May 20, 1941 2,267,732 Hansen. Dec. 30, 1941 2,325,927 Wilbur Aug. 3, 1943 2,404,306 Luck July 16, 1946 2,413,063 Miller Dec. 24, 1946 2,451,632 Oliver Oct. 19, 1948 2,459,730- Williams Jan. 18, 1949 2,466,712

Kenyon Apr. 12, 1949

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