Pre-distortion in RF path in combination with shaping table in envelope path for envelope tracking amplifier
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.
1. A method for amplifying an input signal, comprising:
generating an envelope signal based on the input signal to be amplified by an amplifier;
shaping the envelope signal for controlling an envelope modulated power supply for the amplifier, wherein shaping the envelope signal is based on an indication of a power of the input signal, wherein shaping the envelope signal comprises adjusting a power supply voltage of the amplifier to track the envelope signal while maintaining the power supply voltage above a minimum voltage setting, wherein the power supply voltage is adjusted such that the power supply voltage only tracks the envelope signal while a voltage of the envelope signal is greater than the minimum voltage setting; and
pre-distorting the input signal to be amplified, wherein pre-distorting the input signal is based on the indication of the power of the input signal, wherein pre-distorting the input signal is based on a pre-distortion function and the shaping the envelope signal is based on a shaping function, and wherein the pre-distortion function is set to improve linearity within a linear region of power associated with the input signal and the shaping function is set to improve linearity within a compressed region of power associated with the input signal, wherein the compressed region of power is higher than the linear region of power.
2. The method of claim 1 , wherein:
an output power of the amplifier in the linear region is more dependent on an input power of the amplifier with respect to the compressed region of power associated with the input signal; and
the output power of the amplifier in the compressed region is more dependent on a supply voltage of the amplifier with respect to the linear region of power.
3. The method of claim 1 , wherein shaping the envelope signal comprises adjusting the minimum voltage setting based on an average power level of the input signal.
4. The method of claim 1 , wherein shaping the envelope signal comprises reducing the minimum voltage setting as an average power level of the input signal is reduced.
5. An envelope tracking amplification stage, comprising:
an envelope detector configured to generate an envelope signal based on an input signal to be amplified by an amplifier;
a shaping table configured to shape the envelope signal for controlling an envelope modulated power supply for the amplifier, wherein the shaping table is configured to shape the envelope signal based on an indication of a power of the input signal, wherein shaping the envelope signal comprises adjusting a power supply voltage of the amplifier to track the envelope signal while maintaining the power supply voltage above a minimum voltage setting, wherein the power supply voltage is adjusted such that the power supply voltage only tracks the envelope signal while a voltage of the envelope signal is greater than the minimum voltage setting; and
a pre-distortion block configured to pre-distort the input signal to be amplified, wherein the pre-distortion block is configured to pre-distort the input signal based on the indication of the power of the input signal, wherein the pre-distortion block is configured to pre-distort the input signal based on a pre-distortion function and the shaping table is configured to shape the envelope signal based on a shaping function, and wherein the pre-distortion function is set to improve linearity within a linear region of power associated with the input signal and the shaping function is set to improve linearity within a compressed region of power associated with the input signal, wherein the compressed region of power is higher than the linear region of power.
6. The envelope tracking amplification stage of claim 5 , wherein:
an output power of the amplifier in the linear region is more dependent on an input power of the amplifier with respect to the compressed region of power associated with the input signal; and
the output power of the amplifier in the compressed region is more dependent on a supply voltage of the amplifier with respect to the linear region of power.
7. The method of claim 1 , wherein shaping the envelope signal is based on an average power of the input signal.