US2246158A - Amplifier - Google Patents

Description

June 1941- J. A. WORCESTER; JR 2,246,158

I AMPLIFIER Filed Aug. 17 1959 Fig.1.

AMPLIFIER Inverwtor": oseph A. Worcester, Jr.

His Attorney.

Patented June 17, 1941 2,246,158 AMPLIFIER Joseph A. Worcester, Jr Bridgeport, Conn., assignor to General Electric Company, a. corporation of New York Application August 17, 1939, Serial No. 290,611

' '1 Claims. (01

My invention relates to amplifiers such as are commonly used in radio receivers and it has for one of its objects to effect certain improvements therein with respect to means for securingdegeneration in such amplifiers.

Commonly, the audio frequency amplifiers in radio receivers are provided with degeneration circuits to improve the frequency response characteristic, reduce hum, distortion, and for other reasons. such amplifiers at high frequencies such circuits are likely to become regenerative at those frequencies. One of the objects of my invention is to provide improved means for avoiding such regeneration.

Another object of my invention is to provide means whereby, particularly atthe higher frequencies, two voltages are supplied from the output of the amplifier to the input thereof having such phase relations that the resultant voltage is degenerative even though one of the two voltages becomes regenerative.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention, itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing in which Fig. 1 represents an embodiment of my invention; Figs. 2 and 3 represent certain vector diagrams relating to its operation and Figs. 4 and 5 illustrate modifications.

Referring to the drawing, I have shown therein the audio frequency portion of a conventional radio receiver, this portion comprising a detector including a diode I, which is connected in series with the secondary Winding of a transformer 2 and a diode load resistance 3, the latter being shunted by the usual condenser 4. This circuit is the usual diode detector circuit of a radio receiver to which currents of radio frequency, such as the received signal currents, or if the receiver be one of superheterodyne type, the intermediate frequency currents, are supplied through transformer 2. These currents are rectified by the diode I to produce a direct current potential upon resistance 3 having therein the-audio frequency modulations of the carrier wave. These audio frequency variations are supplied through a condenser 5 to an audio frequency volume control potentiometer 6 from whence they are supplied through a tap connection I to the input circuit of .an audio amplifier 8. Currents amplified by the Due to the phase shift which occurs in amplifier 8 are additionally amplified by push-pull amplifier 9 including electron discharge devices II] and I I. .The output circuit of these discharge devices includes an audio frequency transformer I3 the secondary winding of which is connected across the voice coil of a loud speaker I4.

The amplifier 9 is energized from a suitable source of potential, which is connected between ground and the intermediate point on the primary winding of transformer I3, this point being indicated at 3+ on the drawing. This source, of course, may also supply the potential to the screen grids of discharge devices Ii] and II as well as operating potential to the discharge devices of amplifier 8.

AS previously stated, it is now common practice in radio receivers to utilize degeneration in connection with such amplifiers in order to improve the frequency-response characteristic, reduce distortion, and to reduce the reproduction of such hum currents as may be produced in the system from the power supply source where such source is derived by rectifying potentials from a commercial alternating current circuit, such as the ordinary house lighting circuit. To this end resistances I5 and I6 are included, the resistance l6 being connected between resistance 5 and ground and the resistance I5 being connected between the ungrounded terminal of resistance I6 and the ungrounded terminal of the voice coil of loud speaker I4. Potential is thus supplied from the voice coil of loud speaker I4 through resistance I5 to resistance l6, which is connected between the grid and cathode of the first discharge device in amplifier 8, this potential being supplied to this amplifier in degenerative phase.

In such systems, however, due to certain shunt capacities employed in amplifiers 8 and 9, such as the capacities which are connected between the anodes and cathodes of the various discharge devices, one of which is indicated at I'I on the drawing, phase shift occurs at high frequencies, this phase shift being sufficient at those frequencies to cause the potential supplied through resistance I5 to resistance I5 to be shifted in phase sufficiently to become regenerative. This is not desirable for a number of reasons, one being that it increases the response of the amplifier to extremely high frequencies thereby rendering the amplifier undesirably sensitive to noise currents.

To avoid such regeneration, in accordance with my invention, a second voltage is supplied from the output of the amplifier to the input of the amplifier of such phase that the resultant of the two voltages is degenerative even at the high frequencies. In Fig. 1 this second voltage is supplied to the resistance It through condenser I8. This condenser I8 may comprise the condenser normally connected between the anode of discharge device I I and ground after the manner of condenser II.

In accordance with my invention this condenser is connected to ground through resistance I6. It has such a value that its impedance is high at all frequencies to be amplified relative to the resistance of resistance I6 so that no substantial phase shift in the voltage supplied through it occurs by reason of change in its reactance with frequency. At low frequencies its reactance is so high that the voltage supplied therethrough is insufficient greatly to influence the phase of the resultant of the two voltages. At high frequencies, however, its reactance, although still high relative tothe resistance of resistor I6, is sufficiently low that its voltage very materially affects the phase of the resultant of the two voltages and it is in such a direction that this resultant voltage is maintained in. degenerative phase even at the. higher frequencies.

This operation of the system may be better understood from an inspection of Figs. 2 and 3. Fig. 2 represents the condition. which exists at low frequencies. In this figure c represents the signal voltage supplied by the detector I to the input of amplifier 8; e represents the voltage supplied to. resistance It through resistance I5. this voltage being 180 degrees displaced from the signal voltage e e represents the voltage supplied through condenser I8 from the anode of device I I. Of course the voltage on the anodes of discharge devices It] and II are 180 degrees displaced with respect to each other but this voltage is taken from the anode of the device from which the voltage is in lagging phase with respect to the voltage 6g. The resultant of the two voltages e and 6 is indicated at e Owing to the large impedance of condenser I8 at low frequencies, e is not greatly different either in phase or magnitude from e Fig. 3 represents the condition which exists at high frequencies. It will be seen that the voltage e supplied through resistance I5 is" now shifted to a position where it lags the signal input voltage e by less than 90 degrees. It thus has a regenerative component and tends to increase the amplification at high frequencies. The voltage 6 is still in the quadrature relation with respect to c but is now greatly increased due to the lower reactance of condenser 8 at the high frequencies. The resultant of these two voltages 6.4", has thus not shifted in phase to the extent that e has shifted and is still in degenerative phase even at the highest frequencies to be amplified. In fact in this way any likelihood of a' regenerative condition existing at high frequencies is eliminated.

Fig. 4- represents a modification of my invention which involves an amplifier having two stages I 9 and 20, both amplifiers being of the single ended type as distinct from the push-pull type shown at 9 in Fig. 1. As previously pointed out in Fig. 1 the desired lagging relation of voltage e to that of a is secured by taking this voltage from the proper one of the two discharge devices IE, or II'. This selection is not available in the arrangement of Fig. 4, which does not involve a push-pull amplifier. The same result, however, may be secured by utilizing a resistance 21 between the cathode and ground of the first amplifier IS. The voltage e may then be supplied from the anode of discharge device 20 to the cathode thereof through the condenser I8 which corresponds to the condenser I8 of Fig. 1. The voltage e;' is supplied through resistance I5 to resistance IS in the same way as was done in Fig. 1. These two voltages then combine in the input circuit in the way that is illustrated by the vector diagrams of Figs. 2 and 3.

Fig. 5 shows a further simplification of the arrangement of Fig. 4 in that the circuits are so arranged that resistance 2| serves the purpose of both resistances -2I and I6 of Fig. 4 thus obviating one resistor. Condenser I3 is connected as in Fig. 4. Resistance I5 is, in Fig. 5, connected between. the cathode of discharge device I9 and the opposite side of the secondary Winding of transformer I3 from that shown in Fig. 4, the ground connection to that winding being also positioned on the opposite terminal. In this way the'two voltages e and e both appear upon resistance 21 in proper phase to produce the effects above explained.

While I. have shown particular embodiments of my invention, it will, of course, be understood that I do not wish to be limited thereto since variousmodifications both in the circuit arrangements and in the instrumentalities employed may be made. I. therefore, contemplate by the appended claims tocover any such modifications as fall within the true spirit and scope of my invemtion- What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, an audio amplifier for currents having frequencies extending over a wide range of. audiofrequenci'es, means to supply voltage from the outputof said amplifier to the input thereof in degenerative phase at low frequencies said range, said amplifier .pperating to shift the pham of said voltage at high fre- .quencies in said range to a regenerative phase,

and means to combine with said voltage supplied from the output a second voltage supplied from the output of said amplifier of such phase that the resultant voltage is in degenerative phase at all frequencies throughout said range.

2. The method of maintaining degeneration at high frequencies in an audio amplifier in which large phase shift occurs at such frequencies, which includes supplying from the output to the input of said amplifier two voltages, the resultant of which remains in degenerative phase when one of saidvoltages is supplied in regenerative phase.

3 The method of maintaining degeneration at high. frequencies inan audio amplifier in which large phase shift occurs at such frequencies,

which includes supplying from the output to the input of said amplifier two voltages widely shifted irr phase, one of said voltages being shifted in one direction from the desired phase relation at low frequencies and the other being shifted in the opposite direction from the desired phase relationat high frequencies, and the resultant of which voltages remains in desired phase at all frequencies.

4. The method 01'- maintaining a desired relatlOH over a wide frequency range between the voltage supplied to the input of an amplifier for amplification thereby and a voltage supplied thereto from the output of said amplifier, where large phase in the amplifier occurs at high frequencies-,which includes supplying to said input from the output of the amplifier, two voltages whose phase shifts vary with frequency but the resultant of which remains in the desired phase relation.

5. In combination, an amplifier, an input circuit therefor, a resistance connected between said input circuit and the output of said amplifier to supply voltage from said output to the input in degenerative phase at low frequencies, said amplifier operating to shift the phase of said voltage at high frequencies to a regenerative phase relation, a condenser connected between said output and input, said condenser having sufficiently high impedance at low frequencies that only small voltage is supplied through said condenser to said input circuit and said condenser having sufficiently low impedance at high frequency that the voltage supplied therethrough to said input at high frequency is sufficiently great that the resultant of said voltage and that supplied through said resistance is degenerative at the highest frequencies to be amplified.

6. In combination, an amplifier having an input circuit including a resistance, a resistance and a condenser each connected between the output of said amplifier and said first resistance to impress voltages from said output on said first resistance in quadrature relation, the voltage supplied through said resistance being in degenerative phase at low frequencies and in regenerative phase at high frequencies, and the voltage supplied through said condenser being low at low frequencies relative to that supplied through said resistance, but sufiiciently high at high frequencies that the phase of the resultant voltage on said first resistance is degenerative at said high frequencies.

'7. In combination, an amplifier having a grid, a cathode and an output, said cathode being connected to ground through a resistance, an input circuit coupled to said grid, a condenser connected between said output circuit and said cath-' ode, and a second resistance connected between said output and said input circuit, said second resistance operating to supply between said grid and cathode a voltage having degenerative phase at low frequencies and regenerative phase at high frequencies, said condenser having sufliciently low impedance at high frequencies to produce on said first resistance a voltage which combines with the voltage supplied to said input through said second resistance to produce between said grid and cathode a resultant voltage having a degenerative phase at high frequencies.

JOSEPH A. WORCESTER, JR.

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