Method and apparatus for protecting devices in an RF power amplifier

• US 7,352,240 B2
• Filed: 09/28/2006
• Issued: 04/01/2008
• Est. Priority Date: 08/17/2001
• Status: Expired due to Term

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Silicon Laboratories Incorporated
• Inventors: Dupuis, Timothy J.
• Primary Examiner(s): Shingleton; Michael B
• Application Number:
  US11/536,231
• Publication Number:
  US 20070103238A1
• Time in Patent Office: 551 Days
• Field of Search: 330/298, 330/207.P, 330/278, 330/279, 330/285
• US Class Current: 330/207.00P
• 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 first detector coupled to the output of the RF power amplifier for detecting the output power of the RF power amplifier;

a second detector coupled to one or more nodes in the RF power amplifier for detecting voltages at the one or more nodes, wherein the second detector is comprised of a first voltage detector coupled to the one or more nodes and a second voltage detector coupled to a reference tone;

control circuitry coupled to the first and second detectors and to the power amplifier for controlling the gain of the power amplifier based on the output power of the RF power amplifier detected by the first detector and the detected voltages of the one or more nodes detected by the second detector.

2. The circuit of claim 1, wherein the second detector is a peak detector.

3. The circuit of claim 2, wherein:

the first voltage detector has an input coupled to the one or more nodes; and

a the second voltage detector has an input coupled to the reference tone.

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

5. The circuit of claim 4, wherein the first and second voltage detectors are matched.

6. The circuit of claim 4, wherein the outputs of the first and second voltage detectors are combined by subtracting the output of the second voltage detector from the output of the first voltage detector.

7. The circuit of claim 4, further comprising a divider circuit coupled between the first voltage detector and the one or more nodes.

8. The circuit of claim 7, wherein the divider is comprised of first and second capacitors coupled between the one or more nodes.

9. The circuit of claim 1, wherein the control circuitry decreases the gain of the power amplifier when the second detector detects a voltage above a voltage threshold.

10. The circuit of claim 1, wherein the control circuitry protects devices in the RF power amplifier by decreasing the gain of the power amplifier when the second detector detects a voltage above a voltage threshold at the one or more nodes in the RF power amplifier.

11. A method of protecting devices in an RF power amplifier comprising:

detecting the output power of the RF power amplifier;

detecting the voltage at a first node of the power amplifier by providing a first detector coupled to the first node and a second detector coupled to a reference tone;

determining whether the detected voltage at the first node is higher than a threshold voltage; and

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

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

13. The method of claim 12, wherein the first and second peak detectors are matched.

14. The method of claim 11, 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 voltage of the first node is less than the threshold voltage.

15. The method of claim 12, 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 voltage of the first node is higher than the threshold voltage.

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

detecting the output power of the RF power amplifier;

detecting the voltage at a first node of the RF power amplifier by providing a first detector coupled to the first node and a second detector coupled to a reference tone;

increasing the gain of the power amplifier if the detected output power is less than a desired output power level and if the detected 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 voltage exceeds a threshold voltage.

17. The method of claim 16, wherein the first and second detectors are peak detectors.

18. The method of claim 17, wherein the first peak detector and the second peak detector are matched.

19. The method of claim 17, 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.