US2284894A

US2284894A - Electric wave amplifier

Info

Publication number: US2284894A
Application number: US368416A
Authority: US
Inventors: Michael J Burger
Original assignee: Western Electric Co Inc
Current assignee: AT&T Corp
Priority date: 1940-12-04
Filing date: 1940-12-04
Publication date: 1942-06-02
Anticipated expiration: 1959-06-02
Also published as: NL64201C; FR883260A

Description

Patented June 2, 1942-' ELECTRIC WAVEv `AMPLIFIER ,Michael J. Burger, South ,Ozone Park, N. Y., assignor to Western yElectr-,ic Company, Incorporated, a corporation of New YorkV Application December 4, 1940, Serial No. 368,416

` a claims. (ci. 11s-111) The invention relates to electric wave amplifiers and in particular to the operation of such y amplifiers so as to reduce or eliminate undesired frequency components in the output current.

l An object of the invention is to sec'ure efficient amplification of applied Waves while reducing or suppressing in the output current the even order distortion products. tion is the generation in one element of the amplier of even order distortion products of such magnitude and phase relationship that they substantially neutralize even order distortion products produced in another element of the amplier.

The invention is applicable to electric wave amplifiers for any purpose, but is particularly advantageous'in amplifiers for Waves in the audio frequency range so that, by the neutralization of the harmonic distortion, the reproduced audio frequency currents are free from distortion.

The invention may conveniently be embodied in the known-amplifier system comprising a driver amplifier, and a phase inverter amplifier, conjointly Acontrolling two amplifiers connected in push-pull or opposed relationship though it vis not limited to this particular use. In accordance with the present invention, the circuit ele- 1 ments associated with the inverter` amplifier are so proportioned that the even order distortion products generated in the inverter amplifier are y of such magnitude and phase as to neutralize in the input of the push-pull amplifier the even order distortion products produced by the driver amplifier.

A more complete understanding of the invention may be had from the following detailed description,` together 'with the attached drawing which is a schematic circuit diagram of a typical embodiment of the invention.

Electric waves from any desired source are apthe capacitor 1 to produce a voltage across the A feature of the inven to produce a voltage across the resistor I4 connected across the input circuit of the amplifier I5 forming the other side ofthe push-pull cornbination.` The voutputs of the push-pull amplifiers IU and I5 are supplied in the usual manner to separate primary windings of the transformer IB, and thence through transformer IB to the output circuit. The driver amplifier 5 may be self-biased by the usual cathode resistor I'l, and

similarly the inverter amplifier II may be selfbiased by the cathode resistor I8. The cathode bias resistors may be shunted by the usual bypa s condensers. Power from any suitable sources is supplied to the cathodes and anodes of the various amplifiers in the usual manner.

Assume that an electric wave of fundamental frequency -I-F' is applied to the input circuit of the driver amplifier 5 of sufficient magnitude to heavily load the driver amplifier. The output circuit of the driver amplifier 5 will then contain the fundamental frequency -F and the even order distortion products, which may be represented by +F2,. and these are applied to the input circuit of the push-pull amplifier I0. A portion of the output vof the driver amplifier w-F and -I-F2 is also supplied to the input circuit of the inverter amplifier II. In accordance with the present invention the circuit elements associated with the inverter amplifier II are so proportioned that the inverter amplifier II produces a second order distortion product which has twice the amplitude of the second order distortion'product y produced 'by the driver amplifier 5, vand an amplication such that the output at the fundamental will be equal in magnitude to the output v of the driver stage. The output .of the inverter amplifier Il will comprise the input inverted in phaseand the generated second order distortion products, and will thus comprise -|2F2,V F2 and t-FZ, which is equal to -I-F-l-FZ. The output of the inverter amplifier II will be -l-F-i-FZ, where'- as, the output of the driver amplifier 5 Will be F4-F2. In accordance with the well-known operation of push-pull circuits, the fundamental age across theresistor 6 which is applied through resistors and 9 connected in serial 'relationship across the input circuit of the amplifier I0, forming one side of a push-pull amplifying arrangement. The voltage developed across the resistor v9 is also supplied to the input circuit of the inverter amplifier Il. The output of the inverter amplifier II produces a voltage across the resistor I2, which is applied through the capacitor I3 frequency F supplied to the input circuit-ofr the amplifier I0 and the fundamental frequency +F supplied to the input circuit of the amplifier I5 will be combined in the primary windings of the transformer I6 and supplied through the transformer I6 to any desired load or utilization circuit. On the other hand, the second order distortion product in the output of the driver amplier 5 and the similar 'second order distortion product-in the output of the inverter amplifier II will mutually neutralize each other in the input type of vacuum tube selected, the grid bias and anode voltages for the driver amplifier are selectwhereas C1 was .1 microfarad. Under these coned so that when'the driver amplifier is fully loaded the output voltage applied to the amplifier I will load the amplifier I0 to a desired maximum value. Under these conditions, the driver amplifier 5 will have a known impedance between anode and cathode and should operate into an output circuit having a preferred value of alter-` l5 'nating current impedance which is determined even order distortion products will be 6 decibels greater than the output of even order distortion products from the driver amplifier 5. The relative values of the resistors 8 and 9 are then selected so that the output voltage from the inverter amplifier II applied to the push-pull amplifier I5 will be equal to the output voltage from the driver amplifier 5 applied to the push-pull amplifier l0.

In a practical embodiment of the invention, the driver amplifier 5 and the inverter amplifier II were Western Electric 262-B vacuum tubes and the amplifiers III and I5 were Western Electric 30D-A vacuum tubes. The resistor 6 was 150,000 ohms, the resistor 8 was 400,000 and the resistor 9 was 40,000 ohms,-the biasing resistor I1 being `7,500 ohms. The resistor I2 was 125,000 ohms, the resistor I4 was 300,000 ohms, while the biasing resistor I0 was 6,500 ohms. `Neglecting the,4 coupling capacitors 1 and I3, and assuming input impedance ofthe amplifiers I0 and I5 to 'be infinite, the driver amplifier 5 was working into an alternating current load of some 112,000 ohms whereas the inverter amplifiers II was workinginto an alternating current load impedance of some 88,000 ohms. It should be noted that in order to maintain the proper phase inversion relationship that capacitor I3 must be made considerably larger than capacitor 1. In this typical embodiment CIS was .25 microfarad ditions, the even order distortion products in the output of the push-pull amplifier were reduced some 20 decibels below the value that these products would have if the driver amplifier 5 and the inverter amplifier II were operating under the same conditions, and were respectively associated with circuit elements of the same magnitude.

-What is claimed is:

1. A push-pull amplifier, a driver amplifier for supplying oscillations to one side of said pushpull amplifier and having circuit elements of such constants as to produce a definite ratio of even order distortion products to the fundamental of the applied oscillations, an inverter amplifier having aninput connected to the `output of said driver amplifier and an output connected to the other side of said push-pull amplifier and having circuit elements of such constants asl to produce even order distortion products of the applied oscillations of such magnitude and phase as to substantially neutralize the even order distortion products supplied by said driver amplifierv to said push-pull amplifier.

2. A resistance-capacitance coupled amplifier ccmprisinga driver amplifier, an inverter amplifier, and two amplifiers in push-pull relationship, characterized by the circuit elements associated with the inverter amplifier being so proportioned that the inverter amplifier produces even order distortion products of the applied signal having twice the amplitude of the even order distortion products produced by the driver tube, whereby the even order distortion products supplied by the inverter amplifier to the push-pull amplifiers substantially cancel the even order distortion products supplied by the driver amplifier to said push-pull amplifiers.

3. In combination, a load circuit, a first amplifier for supplying oscillations to said load circuit having circuit elements of such constants as to produce a definite ratio of even order distortion products to the fundamental frequency of the applied oscillations, and a second amplier having an input coupled to the output of said first amplifier for supplying oscillations equal in magnitude and opposed in phase to the oscillation from said first amplifier to said load circuit, having circuit elements of such constants as to produce reven order distortion prod cts of the funy NncrLAEL J. BURGER.