Power amplifier saturation detection and correction method and apparatus

• US 5,278,994 A
• Filed: 06/03/1991
• Issued: 01/11/1994
• Est. Priority Date: 06/03/1991
• Status: Expired due to Term

• Current Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Black, Gregory R., Hietala, Alexander W.
• Primary Examiner(s): Eisenzopf, Reinhard J.
• Assistant Examiner(s): PHAM, CHI H
• Application Number:
  US07/709,737
• Time in Patent Office: 953 Days
• Field of Search: 455/115-117, 455/126, 455/127, 330/278, 330/207 P, 330/298
• US Class Current: 455/126
• CPC Class Codes: H03G 3/3047 for intermittent signals, e.g. burst signals

Abstract

A power amplifier controller for detecting saturation of the power amplifier (203) and corrects the automatic output control voltage (231) to avoid any further saturation. A detector (211) detects the power of the radio frequency (RF) output signal (211) and generates a signal (229) correlated to the detected power. Comparator (217) compares changes in that signal (229) to changes in the voltage of the AOC signal (231). The comparator (217) generates a signal (233) correlated to saturation of the power amplifier (203) for a DSP (223). The DSP (223) checks the status of this signal (233). Upon detecting saturation, an algorithm contained within the DSP methodically reduces the voltage of the AOC signal (231) until there is a change in the power of the RF output signal (211).

Claims

1. A transmitter containing inter alia means for amplifying a first signal and means for controlling the means for amplifying, the means for amplifying having a first and a second input, a first output, a magnitude of amplification and a saturation point, the first signal having a power level, a first frequency and coupled to the first input of the means for amplifying, the magnitude of amplification of the means for amplifying responsive to a voltage of a second signal coupled to the second input of the means for amplifying, the means for controlling comprising:

means for detecting saturation of the means for amplifying, said means for detecting coupled to the first output of the means for amplifying; and

means for setting the magnitude of amplification of the means for amplifying, said means for setting coupled to an output of said means for detecting and coupled to the second input of the means for amplifying, said means for setting further comprising;

means for generating, in absence of detecting saturation, the second signal having voltage equal to the current voltage of the second signal; and

means for generating, while detecting saturation, the second signal having voltage equal to the current voltage of the second signal less a predetermined increment, until the means for amplifying is no longer saturated.

2. A transmitter containing inter alia means for amplifying a first signal and means for controlling the means for amplifying, the means for amplifying having a first and a second input, and a first output and having a saturation point, the first signal having a power level, a first frequency and coupled to the first input of the means for amplifying, the means for amplifying responsive to a voltage of a second signal coupled to the second input of the means for amplifying, the means for controlling comprising:

means for detecting saturation of the means for amplifying, said means for detecting coupled to the first output of the means for amplifying; and

means for generating the second signal responsive to said means for detecting saturation, such that the means for amplifying is no longer saturated, said means for generating the second signal comprises a digital signal processor and a digital to analog converter coupled to an output of said means for detecting and coupled to the second input of the means for amplifying.

3. A method of controlling an amplifier, the amplifier having at least a first and a second input, an output, a saturation point and amplifying a first signal responsive to the voltage of a second signal, the first signal having a power level, a first frequency and coupled to the first input of the amplifier, the second signal coupled to a second input of the amplifier the method of controlling the amplifier comprising the steps of:

detecting the power level of the first amplified signal at the output of the amplifier and generating a fifth signal indicating the detected power level;

determining a difference between the fifth signal and a third signal, the third signal generated to control the power level of the amplifier;

generating a fourth signal corresponding to said difference and indicating saturation of the amplifier or absence thereof;

generating, in absence of saturation, the second signal in accordance with the third signal; and

generating, while indicating saturation, the second signal having a voltage equal to said third signal less a predetermined increment.

4. A method of controlling an amplifier in accordance with claim 3 wherein said step of generating the second signal having a voltage equal to said third signal less a predetermined increment further comprise the steps of:

determining said fourth signal corresponds to the saturation of the amplifier;

decreasing, responsive to determining saturation, the second signal by a first predetermined increment;

waiting a second predetermined increment;

determining said fourth signal does not correspond to the saturation of the amplifier; and

changing said second signal by a third predetermined increment.

5. An improved amplifier and control circuit for controlling amplifier saturation comprising:

means for amplifying a first signal, forming a first amplified signal having a power level, said means for amplifying having a magnitude of amplification;

means for detecting a power level of said first amplified signal and generating a second signal having a voltage indicative of said detected power level;

means for comparing the voltage of the second signal and a voltage of a third signal, generating a saturation detection signal indicating the presence or absence of saturation in the means for amplifying; and

means, responsive to the saturation detection signal, for setting the magnitude of amplification of the means for amplifying coupled to the means for amplifying, the means for setting comprising;

means, in absence of saturation, for generating the third signal having a voltage equal to the voltage of the second signal, and

means, in presence of saturation, for generating the third signal having a voltage equal to the voltage of the second signal less a predetermined increment.

6. An improved amplifier and control circuit in accordance with claim 5 wherein said means for generating the third signal is a digital signal processor and a digital to analog converter.

7. An improved amplifier and control circuit in accordance with claim 5 wherein said means for detecting saturation is a differential amplifier.