US2939087A - Amplifier - Google Patents

Description

May 31, 1960 J. H. DOYLE 2,939,087

AMPLIFIER Original Filed Dec. 27, 1955 ,C/GZL. 52

INVENTOR.

. ANIPLIFIER Continuation of application Serial No. 555,448, Dec. 27, 1955. This application Sept. 21, 1959, Serial No. 841,407

4 Claims. (Cl. 330-70) The present application constitutes a continuation of my application Serial No. 555,448, filed December 27, 1955, now abandoned.

The present invention relates to improvements in electron circuitry and, in particular, to a control circuit which is efiicient in its power handling capabilities so that relatively small tubes may be used.

The arrangement described herein is essentially a cathode follower circuit having means connected in the cathode return circuit so-that essentially a net constant current flows. Such means involves the use of a tube connected in the cathode follower circuitry so as to have a negative resistance. Using this arrangement, relatively high currents may be delivered to an output circuit while dissipating a relatively small amount of heat in the circuit.

An object of the present invention is to provide an improved circuit of this character which is efiicient in its function of controlling the flow of power to an associated output circuit.

Another object of the present invention is to provide an improved cathode follower circuit involving the use of an electron tube to impart a negative resistance in the circuit.

Another object of the present invention is to provide an improved cathode follower circuit in which a substantially constant current flows over a relatively large range of input voltages.

Another object of the present invention is to provide an improved cathode follower circuit in which relatively high amounts of power may be controlled and circulated using small miniature tubes.

Another object of the present invention is to provide an arrangement of this character in which the amount of heat dissipated in the circuit itself is reduced in substantial amount so that a plurality of such cathode follower circuits may be conveniently assembled in a limited space such as in a computer.

Another object of the present invention is to provide which:

Figure 1 is a circuit illustrating features of the present invention.

Figure 2 is graphical representation illustrating the variation of current through three different elements in the circuit shown in Figure l.

The circuit illustrated in Figure 1 includes a tube 10 of the 6AQ5 type having its screen and anode connected nited States Patent to the positive terminal of a BOO-volt source 12. The

, control grid of tube 10 is connected to a source of conground through resistance 24.

v teristic with respect to increasing voltages applied to the It is noted that the resistance 18 provides a feedback connection between the cathode and anode of tube 20 so as to provide positive feedback to such an extent as to cause the tube 20 to have a negative resistance characcontrol grid of tube 10.

In the graphical illustration represented in Figure 2,-

the abscissa represents current, and the current through the designated elements and the ordinates represent the voltage on the output terminal 25. The curve in Figure 2 represents the variation of current through the tube 20 as a junction of the voltage on the output terminal 25. The curve 32 in Figure 2 represents a like variation of the current through the resistance 18 and the curve 33 represents a like variation of the current through resistance 19. These curves are plotted from experimental data, and, as indicated below, the curve 33 deviates somewhat from theory. It is observed that the slope of the line 32 is positive, indicating the positive resistance, whereas the slope of the curve 30 is negative,

indicating a negative resistance. It is noted that the current through resistance 19, which is the sum of the current flowing through resistance 18 and resistance 20, is substantially constant,-

and, in theory, such current should always remain the same at any particular output voltage between, for example, -l00 volts and volts, but in actual practice it varies as much as 2 milliamperes, largely because of nonlinear characteristics and finite gain of the tube 20 which is of the 6U8 type. K

In operation of the circuit at -100 volts output, the current in the tube 20 is 9 milliamperes, in resistance 18 the current is 6 milliamperes, and the current in resistance 19.is 15 milliamperes. At zero output voltage, the current flowing in the tube 20 is 6 milliamperes, l0 milliamperes in resistance 18, and the current in resistance 19 is 16 milliamperes. The circuit as described above is intended to supply 15 milliamperes to a load represented by the block 40 when the output voltage on the output terminal 25 is either 100 volts or +100 volts. With such intended operation, it has been calculated that the total required power (excluding the power required for heating the cathode of the tubes) is 15.3

watts with 1.5 watts of such power being dissipated in.

the output load 40. v

Using a conventional cathode follwer circuit having the same voltage sources of +300 volts and 300 volts, the total power required is 22.5 watts of which 1.5 watts is supplied to an output load comparable to the output load 49. Thus, the efiiciency of the circuit shown in Figure 2 may be represented by 9.8% compared to a figure of 6.67% which represents the eificiency of a conventional cathode follower. As a result, the present arrangement affords a small compact design, and at the same time proving efliciency over standard circuitry by a factor of 47%.

The arrangement thus operates essentially as a cathode follower with an input signal applied thereto as represented by source 14 to produce a constant current flow in the output circuit 40, such current flow being substantially constant in intensity regardless of relatively large variations in intensity of the input signal. This is so because of the shunting efiect of tube 21 through which a portion of the output current from the cathode of tube flows. The resistance of tube 20 is not constant but decreases with increase in intensity of the input signal, i.e., has a negative resistance characteristic, whereby the shunting effect of tube 20 on the output circuit 40 increases to divert a proportionately greater amount of currentfrom the output circuit 41] in such amount that with increasing nput voltage a greater amount of current flows through tube 20 with the current flow through the output circuit 40 remaining substantially constant.

It will be apparent that the disclosed amplifier is of the operational class, so identified because of its intended usages which include operations upon applied input voltages in accordance with the mathematical theorems of the operational calculus. A means for maintaining the current, through the power' output tube of such an amplifier, substantially constant over the full range of infinitely adjustable negative and positive voltage outputs, inclusive of zero value (no voltage output), has long been sought in this computer art in order to facilitate responsive accuracy and the stabilized fidelity of output under ambient conditions which depend upon the heat dissipation of the output vacuum tube. This is uniquely accomplished, according to the present invenion, by series connecting a pair of resistors, one of power supply source. A cooperating shunting triode tube has'its plate to cathode circuit connected across the larger valued resistor while its grid is biased by a circuit that is connected around the smaller valued resistor of this series connected pair. As the current through the larger resistor of the pair increases, the currentthrough the plate circuit of this shunt triode tube is constrained via its grid control, to substantially linearly decrease, thereby closely maintaining the current through the powertubes plate to cathode circuit and through the smaller resistor of the series pair of resistors to a substantially constant value. Such a maintained constant value holds the heat dissipation of the power tube constant for all operational circumstances, so as to stabilize the fidelity of the response that is available at the output terminal which is connected to the cathode of this power output tube.

While the particular embodiments of the present invention have been shown and described, it will be obvi- Qus to those skilled in the art that changes and modifications may be made Without departing from this invention in its broader aspects and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

I claim:

1. Electrical circuitry comprising a first tube having a cathode, an anode and a control grid, a first resistance, a second resistance, a first voltage source and a second voltage source, a series circuit comprising in series, said anode, said cathode, said first resistance, said second resistance and said first and second voltage sources with the positive terminal of said first source being connected to said anode and said cathode being connected to said first resistance, the negative .tenninaL of said second source being connected to said second resistance, and the negative terminal of saidifirst' source being connected at a point ofreference potential to the positive terminal of said second source,a soutce'of input signal, for said control grid and connected thereto, an output circuit in which a substantially constant current flows regardless of relatively largevariations :in intensity in' said input signal connected to said cathode; a second yacuum tube having an anode and a cathode with the-lastmentioned anode being connected .to the cathode of the first-mentioned tube and the cathode of the secondmentioned vacuum tube being connected to the junction point of the first and second resistancesysairi second tube having "a control gridjandiresistance means con-:

meeting the last-mentioned control grid to the junction point of said second' resistance and said second source to operate said second tubeas a negative. resistance tube.

2. An adjustable operational amplifier comprising a connected power output vacuum tube having its plate connected to one terminal of a. positive power supply source and its cathode connected to a power output terminal, a pair of respectively larger and smaller series connected resistorsfwith diifcrcnt resistances of which the larger is connected to the said cathode and the smaller is connectedto one terminal of a cooperating negative power supply source, the other terminal of eachof said positive and negative sources beinginterconnected at a point of reference potential, and a shunted triode'vacuum tube having itsi'plate to cathode circuit connected around the large resistor; its plate connected to the said power output terminal and its grid biased via af'circuit that is shunt connected around the smaller resistor, whereby the current flowing through the power output tubes plate a mate a constant value for all circumstances under which I the operational amplifier i's used.

References Cited'inthe file of this patent UNITED STATES PATENTS 2,579,633- 'Wadzinskia"; Dec. 25, 1951 2,721,908 Moe Oct. 25,1955

FOREIGN PATENTS 540.834' ore tnaznn 0e31, 1941

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