A low-power switched-capacitor passive sigma-delta modulator

A passive 2nd-order sigma-delta modulator using switched-capacitor based filters was designed, fabricated, and tested. A novel 2nd-order single feedback path topology is used. All circuitry is optimized for low power operation through the use of minimum size MOSFETs, component reduction and topology choice. The modulator was fabricated in On Semiconductor´s C5 500-nm process. The implementation achieves a typical SNDR of above 50 dB for tested frequencies of 10 Hz to 3 kHz and has a peak SNDR of 57.8 dB, which corresponds to an ENOB of 9.3 bits. With a 2.5 V supply, the power consumption of the sigma-delta modulator is 6.75 μW. The modulator achieves a FOM of 1.78 pJ/step.