Transfer function regulation
The invention relates to a technique for controlling in an envelope tracking amplification stage, comprising: determining a representation of the output signal of the amplifier; determining a representation of the input signal of the amplifier; adjusting the determined representation of the input signal according to a target characteristic of the amplifier; comparing the adjusted input and determined representation of the output; and generating a control signal in dependence on the comparison.
1. A method for controlling in an envelope tracking amplification stage comprising an amplifier, the method comprising:
determining a representation of an output signal of the amplifier;
determining a representation of an input signal of the amplifier;
adjusting the determined representation of the input signal according to a target characteristic of the amplifier;
comparing the adjusted representation of the input signal and the determined representation of the output signal; and
generating a control signal based on the comparison,
wherein at least one of:
the target characteristic is an AM-AM characteristic, the control signal is an amplitude control signal, and the control signal modifies a shaping function applied to an envelope of the input signal, or
the target characteristic is a PM-PM characteristic, the control signal is a phase control signal, and the control signal modifies a phase of the input signal.
2. The method of claim 1 , wherein modifying the shaping function comprises indexing the shaping function based on the input signal and applying a result of the comparison to the indexed shaping function.
3. The method of claim 1 , further comprising:
measuring the input signal at an input to the amplifier to determine the representation of the input signal.
4. The method of claim 3 , wherein measuring the input signal comprises demodulating the input signal.
5. The method of claim 1 , further comprising:
modulating the input signal at an input to the amplifier; and
measuring the input signal before modulating the input signal to determine the representation of the input signal.
6. The method of claim 1 , further comprising:
measuring the output signal by demodulating the output signal to determine the representation of the output signal.
7. An envelope tracking amplification stage comprising an envelope path and an input signal path, the envelope tracking amplification stage comprising:
a target block configured to adjust a representation of an input signal of an amplifier according to a target characteristic of the amplification stage; and
a comparator configured to compare the adjusted representation of the input signal to a representation of an output signal of the amplifier, and configured to generate a control signal based on the comparison,
wherein at least one of:
the target characteristic is an AM-AM characteristic, and the control signal is an amplitude control signal, the amplitude control signal being configured to modify a shaping function applied to an envelope of the input signal, or
the target characteristic is a PM-PM characteristic, the control signal is a phase control signal, the envelope tracking amplification stage further comprising an element configured to modify the input signal in the input path to the amplifier, receive the control signal, and modify the phase of the input signal.
8. The envelope tracking amplification stage of claim 7 , wherein modifying the shaping function comprises indexing the shaping function based on the input signal and applying a result of the comparison to the indexed shaping function.
9. The envelope tracking amplification stage of claim 7 , wherein the input signal is measured at an input to the amplifier to determine the representation of the input signal.
10. The envelope tracking amplification stage of claim 7 , wherein the input signal is measured at an input to a modulator to determine the representation of the input signal.