A 73.1dB SNDR digitally assisted subsampler for RF power amplifier linearization systems

We present a digitally assisted subsampler, designed to serve as the downconversion path in adaptive predistorters for 800MHz–5.8GHz RF power amplifiers. We use digital averaging to overcome the noise folding problems of subsampling, obtaining a final SNDR of 73.1dB for signals centered about a 2.4GHz carrier. Using quadrature subsampling, we obtain both the I and Q samples from the same physical path and thereby eliminate IQ gain mismatch. When used as part of an adaptive predistortion system, the subsampler enables an EVM improvement of 3.2% and distortion products suppression of up to 7.6dB for 802.11g signals. The subsampler IC, designed in a 90nm CMOS process, consumes 6.0mW from a 1.2V supply.