Predistortion circuit with feedback

• US 4,554,514 A
• Filed: 12/21/1984
• Issued: 11/19/1985
• Est. Priority Date: 12/21/1984
• Status: Expired due to Term

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: RCA Corporation
• Inventors: Kumar, Mahesh, Whartenby, James C.
• Primary Examiner(s): Mullins, James B.
• Assistant Examiner(s): Wan, G.
• Application Number:
  US06/685,241
• Time in Patent Office: 333 Days
• Field of Search: 330/149, 330/294, 330/107, 332/37 R, 332/37 D, 455/295, 455/296, 455/310
• US Class Current: 330/149
• CPC Class Codes: H03F 1/3247 using feedback acting on predistortion circuits H03F1/3264 takes precedence
• CPC Class Codes: H03F 1/3288 to compensate phase shift as a function of the amplitude
• CPC Class Codes: H03F 2200/438 Separate feedback of amplitude and phase signals being present

Abstract

A predistortion circuit for a microwave power amplifier which exhibits phase and amplitude nonlinearities and has a small signal gain equal to a. The phase distortion circuit includes a 180° coupler, a first coupler for coupling a given fraction of the input power to the 180° coupler and a second coupler for coupling the given fraction of the power output from the amplifier, reduced by a, to the 180° coupler. The 180° coupler has a difference output port at which a signal appears which corresponds substantially to the difference in phase between the two signals input to the 180° coupler and has a sum port at which a signal appears which corresponds substantially to the sum in amplitude between the two signals input thereto.

A phase change circuit and attenuator are coupled between the first coupler and input to the power amplifier. Signals related to the signals produced at the difference port and sum port of the 180° coupler are utilized to control the amount of phase change in the phase change circuit and the amount of attenuation in the attenuator circuit to thereby reduce the phase and amplitude nonlinearities of the signal produced by the power amplifier.

Claims

1. A predistortion circuit, for a power amplifier exhibiting phase and amplitude nonlinearities at its output as a function of input power, comprises in combination:

an input terminal coupled to receive a signal to be amplified and an output terminal coupled to the input of said power amplifier;

means coupled to said input terminal for producing a first signal which is a predetermined fraction X of the signal to be amplified;

means coupled to the output of said power amplifier for producing a second signal which is said fraction X of the output power of said amplifier reduced by a value equal to the gain of said amplifier at a small value of input signal,

means responsive to said first and second signals for producing a third signal which is substantially proportional to the phase difference between said first and second signals and producing a fourth signal which is substantially proportional to the sum of the first and second signals; and

means coupled between said input terminal and said output terminal and responsive to said third and fourth signals applied thereto for changing the phase and amplitude of the signal passing therethrough to compensate for nonlinearities of said power amplifier such as to reduce the phase and amplitude nonlinearities in said amplifier output signal from said power amplifier.

2. The combination as set forth in claim 1 wherein said power amplifier is a microwave power amplifier and wherein said signal to be amplified is a signal in the microwave frequency range.

3. The combination as set forth in claim 2 wherein said means responsive to said first and second signals comprises a 180°

coupler.

4. The combination as set forth in claim 2 wherein said means for changing said amplitude comprises an adjustable attenuator.

5. The combination as set forth in claim 3 wherein said means for changing said amplitude comprises an adjustable attenuator.

6. The combination as set forth in claim 2 wherein said means coupled between said input terminal and said output terminal comprises a means responsive to a pair of control signals for altering the gain and phase of input signals applied thereto in accordance with the values of signals applied thereto and further comprises a programmed storage means addressed by said third and fourth signals for generating said pair of control signals at values to reduce said phase and amplitude distortion of the output signal produced by said power amplifier.

7. The combination as set forth in claim 3 wherein said means coupled between said input terminal and said output terminal comprises a means responsive to a pair of control signals for altering the gain and phase of input signals applied thereto in accordance with the values of signals applied thereto and further comprises a programmed storage means addressed by said third and fourth signals for generating said pair of control signals at values to reduce said phase and amplitude distortion of the output signal produced by said power amplifier.

8. The combination as set forth in claim 5 wherein said means coupled between said input terminal and said output terminal comprises a means responsive to a pair of control signals for altering the gain and phase of input signals applied thereto in accordance with the values of signals applied thereto and further comprises a programmed storage means addressed by said third and fourth signals for generating said pair of control signals at values to reduce said phase and amplitude distortion of the output signal produced by said power amplifier.