# US 8,787,850 B2 · Compensating for non-linear capacitance effects in a power amplifier

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- Number: US 8,787,850 B2
- Document ID: US8787850B2
- Status: Granted
- Kind: B2
- Application number: 12/080,066
- Filed: 2008-03-31
- Published: 2009-10-01
- Granted: 2014-07-22
- Earliest claimed: 2008-03-31
- Assignees: Avago Technologies General IP (Singapore) Pte. Ltd.
- Applicants: David E. Bockelman; Vishnu Srinivasan
- Inventors: David E. Bockelman; Vishnu Srinivasan
- Web page: https://patentgrep.com/patent/US8787850B2

## CPC

- H03G 3/00: Gain control in amplifiers or frequency changers
- H03F 1/086: {with FET's}
- H03F 1/14: by use of neutralising means
- H03F 3/19: with semiconductor devices only
- H03F 3/245: {with semiconductor devices only}
- H03F 3/3022: {CMOS common source output SEPP amplifiers (H03F3/3008 takes precedence)}
- H04B 1/40: Circuits
- H03F 2200/451: the amplifier being a radio frequency amplifier
- H03F 2203/30144: the SEPP comprising a reactive element in the amplifying circuits
- H03G: CONTROL OF AMPLIFICATION
- H03F: AMPLIFIERS
- H04B: TRANSMISSION

## Abstract

In one implementation, a power amplifier may include a gain device to receive an input signal and to output an amplified signal, and a compensation device coupled to the gain device to compensate for a change in a capacitance of the gain device occurring due to a change in the input signal. The power amplifier may be formed using a complementary metal oxide semiconductor (CMOS) process.

## Claims

### Claim 1

An apparatus comprising:
a gain device to receive an input signal and to output an amplified signal;
a compensation device coupled to the gain device to compensate for a change in a capacitance of the gain device occurring due to a change in the input signal; and
a bias source coupled to the compensation device to cause a capacitance of the compensation device to change in an opposite direction to the capacitance change of the gain device, wherein the bias source is configured to align predetermined transition regions of the compensation device and the gain device.

### Claim 2 (depends on 1)

The apparatus of claim 1, wherein the compensation device is a complementary device to the gain device.

### Claim 3 (depends on 2)

The apparatus of claim 2, wherein the complementary device is to reduce phase non-linearity of the gain device.

### Claim 4 (depends on 1)

The apparatus of claim 1, wherein the compensation device is smaller than the gain device, and the bias source is to provide a bias voltage corresponding substantially to a difference between a supply voltage level and threshold voltages for the gain device and the compensation device.

### Claim 5 (depends on 2)

The apparatus of claim 2, compensation device is coupled to an input of the gain device.

### Claim 6 (depends on 5)

The apparatus of claim 5, wherein the compensation device comprises a CMOS transistor of a first polarity and the gain device comprises a CMOS transistor of a second polarity, wherein the compensation device has a source terminal and a drain terminal coupled to a bias source and a gate terminal coupled to a gate terminal of the gain device.

### Claim 7

A wireless device comprising:
a transceiver to receive baseband signal information from a baseband processor and to output a radio frequency (RF) signal;
a power amplifier coupled to the transceiver to receive and amplify the RF signal, the power amplifier comprising a complementary metal oxide semiconductor (CMOS) gain stage having a non-linear phase response to the RE signal when a voltage of the RE signal is in a predetermined range, and a compensation circuit comprising:
a variable capacitance element coupled to the CMOS gain stage to compensate for the non-linear phase response; and a bias generator to provide a bias voltage to the capacitance-coupled transistor to cause the capacitance-coupled transistor to have a first capacitance value when the RE signal causes the CMOS gain stage to have a second capacitance that is substantially equal and opposite to the first capacitance when the RF signal is substantially around a threshold voltage of at least one device of the CMOS gain stage, wherein the variable capacitance element comprises a capacitance-coupled transistor coupled to a transistor of the CMOS gain stage of opposite polarity; and
an antenna coupled to the power amplifier to radiate the amplified RF signal.