a second order sigma delta modulator includes a digital to analog converter that provides feedback for system modulation . the digital to analog converter employs a dynamic element matching circuit which randomly selects among main capacitors to reduce the effect of capacitor value mismatching . the digital to analog converter also employs a self calibration circuit to trim the values of the main capacitors to obtain better capacitor matching . during self calibration , a clock signal driving a pseudo random number generator of the dynamic element matching circuit is reduced to assist in minimizing variance in a digital output signal for accurate calibration of the main capacitors . upon completion of calibration , the clock signal is returned to a frequency coinciding with the modulator clock rate .