Automatic filter calibration for bandpass delta-sigma modulators

A bandpass delta-sigma modulator with a widely tunable center frequency range for direct digitization of IF or RF signals can be a key building block for highly digitized radio receivers. The performance of the bandpass modulator is highly dependent on the accuracy of the noise transfer function zero locations in the presence of process spread. An automatic calibration method is proposed to calibrate the noise transfer function zeros to their desired locations based on minimizing the variance of the decimated output bitstream of the modulator. The calibration does not need external test stimuli nor does it require complex hardware.