A passive 2nd-order sigma-delta modulator for low-power analog-to-digital conversion

A passive 2^nd-order sigma-delta modulator based on a cascade of first-order lowpass filters was designed, fabricated, and tested. A lumped RC filter is added in the loop of a conventional 1st-order passive sigma-delta modulator in order to improve the linearity of its transfer function. A low power edge-triggered comparator was designed and fabricated along with lumped components in ON Semiconductor´s C5 500-nm process. The implementation achieved a THD below 1% for all frequencies between 10 Hz and 5 kHz. With a 5 V supply the power consumption of the sigma-delta modulator is 64.5 uW to 150 uW depending on the input signal.