Envelope tracking RF transmitter calibration

A transmitter operative in a wireless communication terminal, comprising:

• an upconverter operative to receive an input signal;
• a power amplifier receiving a variable supply voltage and operative to amplify an upconverter output;
• and
• a downconverter operative to downconvert a power amplifier output;
• and
• a baseband processor operative to receive the downconverter output;
• wherein the input signal to the upconverter is a time repetitive signal umod(t) having a repetition period T and for which an envelope of the input signal |umod(t)| includes all relevant values within a predetermined range and is a slowly time-varying signal;
• a variable supply voltage VPA applied to the power amplifier is a function of the envelope of the input signal |umod(t)|;
• an integer number of samples of the downconverter output Uout_demod(t) are sampled;
• and
• wherein the baseband processor is further operative to:
• sample the downconverter output Uout_demod(t) m times for each repetition period T, where m is an integer;
• for each sampled downconverter output Uout_demod-j, time and phase align the sampled downconverter output Uout_demod-j with the input signal umod-j to generate an aligned output U′out_demod-j, where j=0 . . . m−1, wherein Umod-j is the jth sampled point of the input signal umod(t);
• and
• repeat said sampling and said time and phase aligning over k repetition periods, where k is an integer, and wherein in each repetition i where =0 . . . k−1, the variable supply voltage VPA-i has known values as a function fi of the envelope of the input signal |umod(t)|, using a different function fi for each repetition;
• estimate a gain at each sample point |Gi,j| as a function of the envelope of the time aligned output signal |Uout_demod-i,j′| and the envelope of the input signal |umod-j|;
• and
• calculate a function f where VPA=ƒ(|umod|) yields a desired transmitter gain of |G0| using the gain estimation samples |Gi,j|.

A non-transitory computer readable medium having stored thereon instructions operative to cause a processing circuit in a User Equipment featuring a transmitter including an upconverter receiving an input signal, a power amplifier receiving a variable supply voltage and operative to amplify the upconverter output, and a downconverter operative to demodulate the amplifier output, to perform the steps of:

• applying as the input signal to the upconverter a time repetitive signal umod(t) having a repetition period T and for which an envelope of the input signal |umod(t)| includes all relevant values within a predetermined range and is a slowly time-varying signal;
• applying to the power amplifier a variable supply voltage VPA that is a function of the envelope of the input signal |umod(t)|, wherein the function relating the envelope of the input signal |umod(t)| to the variable supply voltage VPA is determined by:
• sampling the downconverter output Uout_demod(t) m times for each repetition period T, where m is an integer;
• for each sampled downconverter output Uout_demod-j, time and phase aligning the sampled downconverter output Uout_demod-j with the input signal umod-j to generate an aligned output U′out_demod-j, where j=0 . . . m−1, wherein umod-j is the jth sampled point of the input signal umod(t);
• and
• repeating said sampling and said time and phase aligning over k repetition periods, where k is an integer, and wherein in each repetition i where i=0 . . . k−1, the variable supply voltage VPA-i has known values as a function fi of the envelope of the input signal |umod(t)|, using a different function fi for each repetition;
• estimating a gain at each sample point |Gi,j| as a function of the envelope of the time aligned output signal |Uout_demod-i,j′| and the envelope of the input signal |umod-j|;
• and
• calculating a function f where VPA=ƒ(|umod|) yields a desired transmitter gain of |G0| using the gain estimation samples |Gi,j|.