# US 6,720,831 B2 · Power amplifier protection circuit

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- Number: US 6,720,831 B2
- Document ID: US6720831B2
- Status: Granted
- Kind: B2
- Application number: 10/133,793
- Filed: 2002-04-26
- Published: 2003-10-30
- Granted: 2004-04-13
- Earliest claimed: 2002-04-26
- Assignees: RF Micro Devices, Inc.
- Inventors: David Dening; Kathleen Muhonen
- Web page: https://patentgrep.com/patent/US6720831B2

## CPC

- H03F 1/52: Circuit arrangements for protecting such amplifiers {(monitoring arrangements G01R31/28; increasing reliability in communication systems, e.g. using redundancy H04B1/74)}
- H03F 3/19: with semiconductor devices only
- H03F: AMPLIFIERS

## Abstract

A power amplifier circuit comprises a sensing circuit and a processing circuit adapted to detect voltage peaks in an output of a power amplifier. If the voltage peak is above a predetermined threshold level, the processing circuit acts to reduce bias provided to the power amplifier, thereby reducing the output levels.

## Claims

### Claim 1

A power amplifier circuit comprising:
a power amplifier;
a sensing circuit adapted to detect voltage peaks emitted by said power amplifier, said voltage peaks exceeding a predetermined threshold; and
a processing circuit adapted to receive an input from said sense circuit and adjust a bias supplied to said power amplifier to reduce said voltage peaks to a level below said predetermined threshold, wherein said processing circuit comprises a current mirror.

### Claim 2 (depends on 1)

The power amplifier circuit of claim 1 wherein said sensing circuit comprises a transistor.

### Claim 3 (depends on 1)

The power amplifier circuit of claim 1 wherein said sensing circuit comprises a plurality of diodes.

### Claim 4 (depends on 1)

The power amplifier circuit of claim 1 wherein said current mirror acts to reduce bias current supplied to said power amplifier, thereby damping said power amplifier to reduce said voltage peaks.

### Claim 5 (depends on 1)

The power amplifier circuit of claim 1 wherein said processing circuit shunts a portion of a bias current from the power amplifier to ground, thereby reducing the bias applied to the power amplifier.

### Claim 6

A method of controlling a power amplifier comprising:
sensing an output of said power amplifier with a sensing circuit; and
reducing bias supplied to said power amplifier in relation to said output to reduce said output when said output exceeds a predetermined threshold,
wherein reducing bias supplied to said power amplifier comprises mirroring a current from said sensing circuit across a current mirror.

### Claim 7 (depends on 6)

The method of claim 6 wherein sensing an output of said power amplifier comprises sensing the output with an avalanche diode.

### Claim 8 (depends on 6)

The method of claim 6 wherein sensing an output of said power amplifier comprises sensing the output with a diode.

### Claim 9 (depends on 6)

The method of claim 6 wherein sensing an output of said power amplifier comprises sensing the output with a transistor.

### Claim 10 (depends on 6)

The method of claim 6 wherein reducing bias supplied to said power amplifier comprises shunting a portion of a bias current to ground.

### Claim 11

A power amplifier circuit comprising:
a power amplifier comprising an input and an output;
a sensing circuit coupled to said output and detecting peaks in said output, said sensing circuit generating a control signal when a peak above a predetermined threshold is detected; and
a processing circuit receiving said control signal and adjusting a bias signal supplied to said power amplifier to reduce peaks in said output to a level below said predetermined threshold, wherein said processing circuit comprises a current mirror.

### Claim 12

A power amplifier circuit comprising:
a power amplifier comprising an input and an output;
a transistor coupled to said output and sensing voltage peaks above a predetermined threshold in said output; and
a current mirror coupled to said transistor and said input, said current mirror adjusting bias supplied to said input based on voltage peaks detected by said transistor.