# US 2015/0145596 A1 · Adaptive biasing scheme for an amplifier

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- Number: US 2015/0145596 A1
- Document ID: US20150145596A1
- Status: Published application
- Kind: A1
- Application number: 14/554,374
- Filed: 2014-11-26
- Published: 2015-05-28
- Earliest claimed: 2012-05-30
- Assignees: Nujira Limited
- Applicants: Nujira Limited
- Inventors: Russell Fagg
- Web page: https://patentgrep.com/patent/US20150145596A1

## CPC

- H03F 1/0222: {by using a signal derived from the input signal}
- H03F 1/0266: {by using a signal derived from the input signal}
- H03F 1/30: Modifications of amplifiers to reduce influence of variations of temperature or supply voltage {or other physical parameters (in differential amplifiers H03F3/45479)}
- H03F 3/45479: {characterised by the way of common mode signal rejection}
- H03F 2200/102: A non-specified detector of a signal envelope being used in an amplifying circuit
- H03F 2203/45112: the biasing of the differential amplifier being controlled from the input or the output signal
- H03F: AMPLIFIERS

## Abstract

There is provided a bias arrangement for an amplifier adapted to amplify a varying input signal, the arrangement comprising a control circuit arranged to adaptively vary a bias current to the amplifier in dependence on an envelope of the varying input signal.

## Claims

### Claim 1

A bias arrangement for an amplifier adapted to amplify a varying input signal, the arrangement comprising:
a current source configured to generate a bias current; and
a control circuit configured to adaptively vary the bias current to the amplifier in dependence on an envelope of the varying input signal, the control circuit including a peak detection circuit configured to track the envelope of the varying input signal and to provide an output, which is proportional to the instantaneous magnitude of the varying input signal, for controlling the variation of the bias current.

### Claim 2 (depends on 1)

The bias arrangement of claim 1 wherein the control circuit includes a bias modulation circuit responsive to the output of the peak detection circuit and arranged to control the current source in dependence thereon.

### Claim 3 (depends on 1)

The bias arrangement of claim 1 further comprising:
a common mode detection circuit configured to detect a common mode voltage associated with the varying input signal, and
a current generator configured to generate a DC offset current in the bias current in dependence on the detected common mode voltage.

### Claim 4 (depends on 1)

The bias arrangement of claim 1 wherein the amplifier is a transconductance amplifier.

### Claim 5 (depends on 4)

An envelope-tracking supply for an amplification stage including a transconductance amplifier according to claim 4.

### Claim 6 (depends on 1)

A mobile communication handset including an envelope tracking power supply for a radio frequency amplifier including an amplifier according to claim 1.

### Claim 7 (depends on 1)

A mobile communication infrastructure device including an envelope tracking power supply for a radio frequency amplifier including an amplifier according to claim 1.

### Claim 8

A bias arrangement for a transconductance amplifier arranged to amplify a varying input signal, the arrangement comprising:
a peak detection circuit configured to track the envelope of an input signal for the transconductance amplifier and to provide an output which is proportional to the instantaneous magnitude of the input signal; and
a bias modulation circuit responsive to the peak detection circuit and arranged to modulate a bias current to the transconductance amplifier in accordance with the envelope of the input signal.

### Claim 9 (depends on 8)

The bias arrangement of claim 8 further comprising a current source for providing the bias current under the control of the bias modulation circuit.

### Claim 10

A method of providing a bias current to an amplifier arranged to amplify a varying input signal, the method comprising:
(a) varying the bias current in dependence on the envelope of the varying input signal by tracking the envelope of the varying input signal; and
(b) providing an output which is proportional to the instantaneous magnitude of the varying input signal for controlling the variation of the bias current.

### Claim 11 (depends on 10)

The method of claim 10 further comprising detecting a common mode voltage associated with the varying input signal, and generating a DC offset current in the bias current in dependence on the detected common mode voltage.

### Claim 12 (depends on 10)

The method according to claim 10 applied to a transconductance amplifier.

### Claim 13 (depends on 12)

The method according to claim 12 applied to the transconductance amplifier of an envelope tracking power supply for a radio frequency amplifier.