Method and apparatus for protecting devices in an RF power amplifier

• US 20040070457A1
• Filed: 09/29/2003
• Published: 04/15/2004
• Est. Priority Date: 08/17/2001
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Silicon Laboratories Incorporated
• Inventors: Dupuis, Timothy J.
• Granted Patent: US 7,145,396 B2
• Time in Patent Office: Days
• US Class Current: 330/298
• CPC Class Codes: H03F 1/52 Circuit arrangements for protecting such amplifiers monitoring arrangements G01R31/28; increasing reliability in communication systems, e.g. using redundancy H04B1/74
• CPC Class Codes: H03G 3/3042 in modulators, frequency-changers, transmitters or power amplifiers transmission power control in bidirectional transmission systems H04W52/04
• CPC Class Codes: H03G 3/3047 for intermittent signals, e.g. burst signals

Abstract

A method and apparatus are provided for use with a power amplifier for protecting active devices on the power amplifier. A peak detector is used by control circuitry to detect the presence of a peak voltage that exceeds a threshold voltage. In response to the detection of a peak voltage, the gain of the power amplifier is reduced.

Claims

1. A circuit for protecting devices in an RF power amplifier comprising:

a peak detector coupled to an output of the power amplifier for detecting peak voltages at the output of the power amplifier; and

control circuitry coupled to the peak detector and to the power amplifier for controlling the gain of the power amplifier, wherein the control circuitry decreases the gain of the power amplifier when the peak detector detects a voltage above a voltage threshold.

2. The circuit of claim 1, wherein the peak detector further comprises:

a first peak detector having an input coupled to the output of the power amplifier; and

a second peak detector having an input coupled to a reference tone.

3. The circuit of claim 2, wherein outputs of the first and second peak detectors are combined to provide a peak detection signal to the control circuitry.

4. The circuit of claim 3, wherein the first and second peak detectors are matched.

5. The circuit of claim 3, wherein the outputs of the first and second peak detectors are combined by subtracting the output of the second peak detector from the output of the first peak detector.

6. The circuit of claim 3, further comprising a divider circuit coupled between the first peak detector and the output of the power amplifier.

7. The circuit of claim 1, wherein the divider is comprised of a first and second capacitor coupled between the output of the power amplifier and ground.

8. The circuit of claim 1, further comprising a power detector coupled to the output of the power amplifier and to the control circuitry for detecting the output power of the power amplifier.

9. A circuit comprising:

an RF power amplifier having an input and an output;

a peak detector coupled to the power amplifier for detecting a peak voltage at a node of the power amplifier; and

power control circuitry coupled to the peak detector and to the power amplifier for controlling the gain of the power amplifier, wherein the power control circuitry limits the power at the output of the power amplifier when the peak detector detects a peak voltage greater than a threshold voltage.

10. The circuit of claim 9, wherein the peak detector is comprised of first and second matched peak detectors.

11. The circuit of claim 10, wherein the first peak detector is coupled to the output of the power amplifier and the second peak detector is coupled to a reference tone.

12. The circuit of claim 11, wherein the first and second peak detectors are matched.

13. The circuit of claim 9, further comprising a power detector coupled to the output of the power amplifier and to the power control circuitry for detecting the output power of the power amplifier.

14. A method of protecting devices in an RF power amplifier comprising the steps of:

detecting a peak voltage at a first node of the power amplifier;

determining whether the detected peak voltage is higher than a threshold voltage; and

if it is determined that the detected peak voltage is higher than the threshold voltage, decreasing the gain of the power amplifier.

15. The method of claim 14, further comprising the step of detecting the output power of the power amplifier.

16. The method of claim 15, wherein the gain of the power amplifier is increased if the detected output power is less than a desired power level, and if the detected peak voltage is lower than the threshold voltage.

17. The method of claim 15, wherein the gain of the power amplifier is decreased if the detected output power is greater than a desired power level, or if the detected peak voltage is higher than the threshold voltage.

18. The method of claim 14, wherein the peak voltage is detected using the steps of:

providing a first peak detector coupled to the output of the power amplifier; and

providing a second peak detector coupled to a reference tone.

19. The method of claim 18, wherein the first and second peak detectors are matched.

20. A method of controlling an RF power amplifier comprising the steps of:

detecting the output power of the RF power amplifier;

detecting a peak voltage at a first node of the power amplifier;

increasing the gain of the power amplifier if the detected output power is less than a desired output power level and if the detected peak voltage does not exceed a threshold voltage; and

decreasing the gain of the power amplifier if the detected output power is greater than the desired output power level or if the detected peak voltage exceeds a threshold voltage.

21. The method of claim 20, wherein the step of detecting a peak voltage is performed using a peak detector.

22. The method of claim 20, wherein the step of detecting a peak voltage further comprises the steps of:

providing a first peak detector coupled to the power amplifier;

providing a second peak detector coupled to a reference tone; and

combining the outputs of the first and second peak detectors.

23. The method of claim 22, wherein the first peak detector and the second peak detector are matched.

24. The method of claim 22, wherein the outputs of the first and second peak detectors are combined by subtracting the output of the second peak detector from the output of the first peak detector.