Envelope tracking system for MIMO
There is disclosed an amplifier arrangement comprising a plurality of amplifiers each arranged to amplify one of a plurality of different input signals, the arrangement comprising an envelope tracking modulator for generating a common power supply voltage for the power amplifiers, and further comprising an envelope selector adapted to receive a plurality of signals representing the envelopes of the plurality of input signals, and adapted to generate an output envelope signal representing the one of the plurality of envelopes having the highest level at a particular time instant as the input signal for the envelope tracking modulator.
1. An amplifier arrangement comprising a plurality of amplifiers each arranged to amplify one of a plurality of different input signals, the arrangement comprising an envelope tracking modulator for generating a common power supply voltage for the power amplifiers, and further comprising an envelope selector adapted to receive a plurality of signals representing the envelopes of the plurality of different input signals, and adapted to generate an output envelope signal representing the one of the plurality of envelopes having the highest level at a particular time instant as an input signal for the envelope tracking modulator.
2. The amplifier arrangement of claim 1 wherein the envelope selector is arranged to generate a composite envelope signal as the output envelope signal.
3. The amplifier arrangement of claim 2 wherein the composite envelope signal transitions between the envelopes of ones of the plurality of different input signals in dependence upon the one of the plurality having the instantaneous largest amplitude.
4. The amplifier arrangement of claim 1 further comprising a plurality of envelope processing stages each for receiving one of the plurality of different input signals and for generating a signal representing the envelope of said input signal.
5. The amplifier arrangement of claim 4 wherein each of the envelope processing stages includes a non-linear mapping stage for mapping its input to its output.
6. The amplifier arrangement of claim 4 wherein each of the envelope processing stages includes a delay for delaying the signal in the supply path relative to the signal in the input path to the amplifier.
7. The amplifier arrangement of claim 2 further including a moving average filter to remove discontinuities from the composite envelope signal.
8. The amplifier arrangement of claim 2 further comprising a plurality of pre-distortion stages, for receiving the respective plurality of input signals, and further arranged to receive said composite envelope signal, and provide a pre-distorted input signal to the input of the respective power amplifier.
9. The amplifier arrangement according to claim 8 further comprising a feedback receiver arranged to selectively receive the output of one of the plurality of amplifiers and selectively provide an additional input to the one of the plurality of pre-distortion stages associated with the amplifier, to adaptively adjust the pre-distortion coefficients of the pre-distortion stage to minimize distortion at the output of the amplifier.
10. The amplifier arrangement of claim 9 wherein the feedback receiver is arranged to switch between all of the plurality of amplifiers in a sequence.
11. The amplifier arrangement of claim 1 wherein the plurality of different input signals are derived from a common signal source.
12. A multi-input, multi-output, MIMO, transmitter stage including an amplifier arrangement according to claim 1 .
13. The MIMO transmitter stage of claim 12 for use in a cellular base station.
14. A method of amplification in an amplifier arrangement comprising a plurality of amplifiers each arranged to amplify one of a plurality of different input signals, the method comprising providing an envelope tracking modulator for generating a common power supply voltage for the plurality of amplifiers, the method further comprising receiving a plurality of signals representing the envelopes of the plurality of different input signals, and generating an output envelope signal representing the one of the plurality of envelopes having the highest level at a particular time instant as an input signal for the envelope tracking modulator.