Adaptive biasing scheme for an amplifier
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.
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, 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.
2. 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.
3. The bias arrangement of claim 1 wherein the amplifier is a transconductance amplifier.
4. An envelope-tracking supply for an amplification stage including a transconductance amplifier according to claim 3 .
5. A mobile communication handset including an envelope tracking power supply for a radio frequency amplifier including the amplifier according to claim 1 .
6. A mobile communication infrastructure device including an envelope tracking power supply for a radio frequency amplifier including the amplifier according to claim 1 .
7. A bias arrangement for a transconductance amplifier arranged to amplify a varying input signal, the arrangement comprising:
a peak detection circuit configured to track an 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;
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; and
a current source for providing the bias current under the control of the bias modulation circuit.
8. 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 an envelope of the varying input signal by tracking the envelope of the varying input signal;
(b) providing an output current which is proportional to the instantaneous magnitude of the varying input signal for controlling the variation of the bias current; and
(c) modulating a current source in dependence on the output current for controlling the amplifier.
9. The method of claim 8 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.
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.