Abstract: There is disclosed a method of controlling an input to an envelope modulated power supply of an envelope tracking amplification stage, comprising: generating an envelope signal representing the envelope of a signal to be amplified; applying a shaping function to the envelope signal to generate a shaped envelope signal, including: clipping the shaped envelope signal at high input envelope values; and providing the shaped envelope signal as an input signal to the envelope modulated power supply.

Abstract: There is disclosed a method of controlling an envelope tracking amplification stage comprising an envelope modulated power supply, the method comprising: determining a shaping function to be applied to an envelope signal for controlling the envelope modulated power supply in dependence on a system linearity objective in a region of operation of the amplifier in which the output power of the amplifier is dependent upon the supply voltage; and determining a pre-distortion function to be applied to an input signal to be amplified in dependence on a further linearity objective of the system, in a region of operation of the amplifier in which the output of the amplifier is dependent upon the input power to the amplifier.

Abstract: An amplification stage comprising: a combiner to generate a sum input signal by combining a voltage signal with a DC bias voltage; a subtractor to generate a difference input signal by subtracting the voltage signal from the DC bias voltage; a first transistor for generating a first part of an amplifier output signal from the sum input signal; a second transistor for generating a second part of an amplifier output signal from the difference input signal; a combiner for combining the first and second parts of the amplifier output signal; a sensing circuit arranged to sense a current flowing in each of the first and second transistors; a control circuit arranged to determine the quiescent current of the first and second transistors in dependence on the sensed currents; and an adjustment circuit arranged to adjust the DC bias voltage in order to minimise variation in the quiescent current.

Abstract: There is disclosed a method of determining an AM-PM distortion measurement for an amplifier, the method comprising: generating a test waveform to be provided to the input of the amplifier; periodically puncturing the test waveform with a fixed-level reference signal to generate a modified test waveform which alternates between test periods in which a portion of the test waveform is present and reference periods in which the fixed-level reference signal is present; measuring the amplifier AM-PM distortion in a test period; measuring the phase difference between the input and the output of the amplifier in reference periods either side of the test period; estimating a phase error in the test period in dependence on phase differences measured in the reference periods; and estimating the true amplifier AM-PM distortion by removing the estimated phase error from the measured amplifier AM-PM distortion.