Adaptive biasing scheme for an amplifier

1. 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;

a common mode detection circuit for detecting a common mode voltage associated with the varying input signal; and

a current generator for generating a DC offset current in the bias current in dependence on the detected common mode voltage.

2. The bias arrangement of claim 1 further including a current source for generating the bias current.

3. The bias arrangement of claim 1 wherein the control circuit includes a peak detection circuit arranged 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 to the bias modulation circuit for controlling the variation of the bias current.

4. The bias arrangement of claim 3 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.

5. An envelope-tracking supply for an amplification stage including a bias arrangement for a transconductance 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.

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

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

8. A method of providing a bias current to an amplifier arranged to amplify a varying input signal, the method comprising:

varying the bias current in dependence on the envelope of the varying input signal;

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.

9. A method according to claim 8 further comprising providing an output which is proportional to the instantaneous magnitude of the varying input signal for controlling the variation of the bias current.

10. The method according to claim 8 applied to a transconductance amplifier.

11. The method according to claim 8 applied to the transconductance amplifier of an envelope tracking power supply for a radio frequency amplifier.