COMMUNICATION UNIT, DIGITAL BAND-PASS SIGMA-DELTA MODULATOR AND METHOD THEREFOR

摘要

A communication unit comprises a power DAC. The DAC comprises: a switched mode power amplifier (SMPA); and a digital band-pass sigma-delta modulator operably coupled to the SMPA. The sigma-delta modulator comprises an input to receive an input baseband signal; a delay; an adder module arranged to add a feedback signal with an output from the delay; and at least two feedback branches. The sigma-delta modulator is arranged to digitally oversample the input baseband signal such that a ratio of a sampling frequency employed by the sigma-delta modulator to a radio frequency (RF) output from the DAC is fixed and the sampling frequency tuned or wherein the sampling frequency is fixed and the ratio is adjusted, such that a first feedback branch in the sigma-delta modulator is formed using at least one from a group of: a zero gain, an additive inverse of a second feedback branch.

主权项

1. A communication unit comprising a power digital to analog converter comprising:
a switched mode power amplifier; a digital band-pass sigma-delta modulator operably coupled to the switched mode power amplifier and comprising:
an input to receive an input baseband signal;at least one delay;at least two feedback branches; andat least one adder module arranged to add at least one feedback signal with an output from the at least one delay, wherein the digital band-pass sigma-delta modulator is arranged to digitally oversample the input baseband signal such that a ratio of a sampling frequency employed by the digital band-pass sigma-delta modulator to a radio frequency (RF) output from the power digital to analog converter is fixed and the sampling frequency is tuned or wherein the sampling frequency is fixed and the ratio is adjusted, such that at least one first feedback branch in the digital band-pass sigma-delta modulator is formed using at least one from a group of: a zero gain, an additive inverse of a second feedback branch.