Method and apparatus for reducing off-channel interference produced by a linear transmitter

• US 5,574,992 A
• Filed: 04/29/1994
• Issued: 11/12/1996
• Est. Priority Date: 04/29/1994
• Status: Expired due to Term

• Current Assignee: Motorola Solutions, Inc.
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Gailus, Paul H., Cygan, Lawrence F., Baker, Michael H., Turney, William J.
• Primary Examiner(s): Eisenzopf, Reinhard J.
• Assistant Examiner(s): Nguyen, Lee
• Application Number:
  US08/235,415
• Time in Patent Office: 928 Days
• Field of Search: 455/126, 455/127, 455/63, 455/115, 455/67.1, 455/67.3, 455/50.1, 455/93, 455/116, 330/107, 330/129, 330/149, 330/109, 330/75
• US Class Current: 455/126
• CPC Class Codes: H03F 1/3247 using feedback acting on predistortion circuits H03F1/3264 takes precedence
• CPC Class Codes: H03F 1/3294 Acting on the real and imaginary components of the input signal
• CPC Class Codes: H03F 1/34 Negative-feedback-circuit arrangements with or without positive feedback H03F1/02 - H03F1/30, H03F1/38 - H03F1/50, H03F3/50 take precedence ; for rejection of common mode signals H03F3/45479
• CPC Class Codes: H03F 2200/57 Separate feedback of real and complex signals being present
• CPC Class Codes: H03F 3/24 of transmitter output stages
• CPC Class Codes: H04B 1/0475 with means for limiting noise, interference or distortion H04B1/0483 takes precedence
• CPC Class Codes: H04B 2001/0433 with linearisation using feedback

Abstract

A linear transmitter (100), which utilizes closed loop feedback to maintain its linearity, employs a method for reducing off-channel interference produced by the linear transmitter (100). A dynamically alterable parameter source (DAPS, 126) is provided to the linear transmitter (100). The DAPS (126) is then used to adjust at least one loop parameter of the closed loop feedback such that off-channel interference is reduced.

Claims

1. In a linear transmitter that includes an information signal source and a power amplifier having a varying load impedance, the linear transmitter utilizing a closed loop feedback path to maintain linearity, wherein the closed loop feedback path includes a loop phase adjusting circuit, a method for reducing off-channel interference comprising the steps of:

A) providing a dynamically alterable parameter source;

B) measuring the varying load impedance to produce a measured load impedance;

C) inputting the measured load impedance to the dynamically alterable parameter source;

D) producing, by the dynamically alterable parameter source, a loop phase adjustment value base on the measured load impedance;

E) inputting the loop phase adjustment value to the loop phase adjusting circuit; and

F) adjusting, by the loop phase adjusting circuit, a phase value for the closed loop feedback path based, at least in part, on the loop phase adjustment value.

2. In a linear transmitter that includes an information signal source and a power amplifier having a varying load impedance, the linear transmitter utilizing a closed loop feedback path to maintain linearity, and the closed loop feedback path including a loop phase adjusting circuit, a method for reducing off-channel interference comprising the steps of:

A) providing a dynamically alterable parameter source;

B) providing a training signal within a training interval;

C) at times falling substantially within the training interval, measuring the varying load impedance to produce a measured load impedance;

D) inputting the measured load impedance to the dynamically alterable parameter source;

at times falling substantially outside the training interval,

E) using the dynamically alterable parameter source to produce a loop phase adjustment value based on the measured load impedance;

F) inputting the loop phase adjustment value to the loop phase adjusting circuit; and

G) adjusting, by the loop phase adjusting circuit, loop phase of the closed loop feedback path based on the loop phase adjustment value, thereby reducing off-channel interference produced during the training interval and at times falling substantially outside the training interval.

3. The method of claim 2, wherein the closed loop feedback path further includes a loop gain adjusting circuit, the method further comprising the steps of:

at times falling substantially outside the training interval,

H) using the dynamically alterable parameter source to produce a loop gain adjustment value based on the measured load impedance;

I) inputting the loop gain adjustment value to the loop gain adjusting circuit; and

J) adjusting, by the loop gain adjusting circuit, loop gain of the closed loop feedback path based on the loop gain adjustment value, thereby reducing off-channel interference produced during the training interval and at times falling substantially outside the training interval.

4. The method of claim 2, wherein the linear transmitter further includes a signal level adjusting circuit, the method further comprising the steps of:

at times falling substantially outside the training interval,

H) using the dynamically alterable parameter source to produce a signal level adjustment value based on the measured load impedance;

I) inputting the signal level adjustment value to the signal level adjusting circuit; and

J) adjusting, by the signal level adjusting circuit, an amplitude of a signal produced by the information signal source based on the signal level adjustment value, thereby reducing off-channel interference produced during the training interval and at times falling substantially outside the training interval.

5. A linear transmitter that utilizes a closed loop feedback path to maintain linearity, the closed loop feedback path including an amplifier that is terminated with a radiating load element during normal operation, the linear transmitter comprising:

a switch for terminating an output of the amplifier with a non-radiating loading circuit, wherein the non-radiating loading circuit comprises a load impedance synthesizer and a load measuring device; and

means, operably coupled to the non-radiating loading circuit, for adjusting at least one loop parameter of the closed loop feedback path when the output of the amplifier is terminated with the non-radiating loading circuit.

6. A linear transmitter that utilizes a closed loop feedback path to maintain linearity, the closed loop feedback path including an amplifier that is terminated with a radiating load element during normal operation, the linear transmitter comprising:

a PIN diode and a biasing circuit for terminating an output of the amplifier with a non-radiating loading circuit, wherein the non-radiating loading circuit comprises an isolator and a constant loading element; and

means, operably coupled to the non-radiating loading circuit, for adjusting at least one loop parameter of the closed loop feedback path when the output of the amplifier is terminated with the non-radiating loading circuit.

7. In a linear transmitter that includes an information signal source and a power amplifier having a varying load impedance, the linear transmitter utilizing a closed loop feedback path to maintain linearity, and the closed loop feedback path including a loop gain adjusting circuit, a method for reducing off-channel interference comprising the steps of:

A) providing a dynamically alterable parameter source;

B) providing a training signal within a training interval;

C) at times falling substantially within the training interval, measuring the varying load impedance to produce a measured load impedance;

D) inputting the measured load impedance to the dynamically alterable parameter source;

at times falling substantially outside the training interval,

E) using the dynamically alterable parameter source to produce a loop gain adjustment value based on the measured load impedance;

F) inputting the loop gain adjustment value to the loop gain adjusting circuit; and

G) adjusting, by the loop gain adjusting circuit, loop gain of the closed loop feedback path based on the loop gain adjustment value, thereby reducing off-channel interference produced during the training interval and at times falling substantially outside the training interval.

8. In a linear transmitter that includes an information signal source, a power amplifier having a varying load impedance, and a signal level adjusting circuit, the linear transmitter utilizing a closed loop feedback path to maintain linearity, a method for reducing off-channel interference comprising the steps of:

A) providing a dynamically alterable parameter source;

B) providing a training signal within a training interval;

C) at times falling substantially within the training interval, measuring the varying load impedance to produce a measured load impedance;

D) inputting the measured load impedance to the dynamically alterable parameter source;

at times falling substantially outside the training interval,

E) using the dynamically alterable parameter source to produce a signal level adjustment value based on the measured load impedance;

F) inputting the signal level adjustment value to the signal level adjusting circuit; and

G) adjusting, by the signal level adjusting circuit, an amplitude of a signal produced by the information signal source based on the signal level adjustment value, thereby reducing off-channel interference produced during the training interval and at times falling substantially outside the training interval.