Recalibration of envelope tracking transfer function during active transmission

A method for adjusting a nonlinear transfer function of an envelope tracking power supply for a power amplifier, comprising:

• supplying an output signal of the power amplifier to a feedback receiver to obtain a feedback signal;
• determining an assumed performance of the power amplifier by evaluating the nonlinear transfer function at a first value defined by an input signal for a transmitter comprising the power amplifier;
• determining an actual performance of the power amplifier by evaluating the nonlinear transfer function at a second value defined by the feedback signal;
• and
• determining a correctional value for a parameter of the nonlinear transfer function based on a difference between the assumed performance and the actual performance;
• wherein the nonlinear transfer function models a power amplifier supply voltage as a function of a voltage of the input signal;
• wherein determining the assumed performance comprises determining a first power supply voltage by evaluating the nonlinear transfer function at the voltage of the input signal as the first value;
• wherein determining the actual performance comprises determining a second power supply voltage by evaluating the nonlinear transfer function at a voltage of the feedback signal as the second value;
• and
• wherein determining the correctional value comprises evaluating a quotient of the first power supply voltage and the second power supply voltage.

A method for re-calibrating a nonlinear transfer function of an envelope tracking power supply for a power amplifier during active transmission, comprising:

• supplying an output signal of the power amplifier to a feedback receiver to obtain a feedback signal;
• determining a total gain of a transmitter comprising the power amplifier based on the feedback signal and a corresponding input signal to the transmitter;
• determining an actual power amplifier gain based on the total gain and a known gain setting of the transmitter;
• and
• determining a correctional value for a parameter of the nonlinear transfer function based on a difference between the actual power amplifier gain and a target gain for the power amplifier.

An envelope tracking system, comprising:

• a transmitter comprising an envelope tracking power amplifier;
• a supply voltage provider configured to provide a variable supply voltage for the envelope tracking power amplifier based on an input signal of the transmitter and a nonlinear transfer function of the variable supply voltage based on the input signal;
• a feedback receiver configured to receive an output signal of the envelope tracking power amplifier and provide a corresponding feedback signal;
• and
• a transfer function adjuster configured to receive the input signal and the feedback signal, and determine a correctional value for the nonlinear transfer function based on a difference between an assumed performance of the envelope tracking power amplifier and an actual performance of the envelope tracking amplifier, the assumed performance being determined based on the input signal and the nonlinear transfer function and the actual performance being determined based on the feedback signal
• wherein the nonlinear transfer function models a power amplifier supply voltage as a function of a voltage of the input signal;
• wherein determining the assumed performance comprises determining a first power supply voltage by evaluating the nonlinear transfer function at the voltage of the input signal;
• wherein determining the actual performance comprises determining a second power supply voltage by evaluating the nonlinear transfer function at a voltage of the feedback signal;
• and
• wherein determining the correctional value comprises evaluating a quotient of the first power supply voltage and the second power supply voltage.

A mobile communication device, comprising:

• an RF circuit configured to provide or receive RF signals;
• and
• an antenna port coupled to the RF circuit;
• wherein the RF circuit comprises an envelope tracking system, the envelope tracking system comprising:
• a transmitter comprising an envelope tracking power amplifier;
• a supply voltage provider configured to provide a variable supply voltage for the envelope tracking power amplifier based on an input signal of the transmitter and a nonlinear transfer function that is a function of the input signal;
• a feedback receiver configured to receive an output signal of the envelope tracking power amplifier and provide a corresponding feedback signal;
• and
• a transfer function adjuster configured to determine a total gain of the transmitter based on the input signal and the feedback signal, derive an actual power amplifier gain based on the total gain and a known gain setting of the transmitter, and determine a correctional value for the nonlinear transfer function based on a difference between the actual power amplifier gain and a target gain for the power amplifier.

An envelope tracking system, comprising:

• a transmitter comprising an envelope tracking power amplifier;
• a lookup table having stored at least one nonlinear transfer function of a variable supply voltage based on an input signal to the transmitter, wherein the lookup table is configured to provide in response to an input signal value a variable supply voltage value;
• a DC-DC converter configured to provide the variable supply voltage for the envelope tracking power amplifier based on the variable supply voltage value provided by the lookup table;
• a feedback receiver configured to receive an output signal of the envelope tracking power amplifier and provide a corresponding feedback signal;
• and
• a transfer function adjuster configured to determine a total gain of the transmitter based on the input signal and the feedback signal, to derive an actual power amplifier gain based on the total gain and a known gain setting of the transmitter, and determine a correctional value for a parameter of the nonlinear transfer function based on a difference between the actual power amplifier gain and a target gain for the power amplifier.