A continuous time delta-sigma modulator with reduced clock jitter sensitivity through DSCR feedback

Abstract

The performance of continuous time delta-sigma modulators is limited by their large sensitivity to feedback pulse-width variations caused by clock jitter in their feedback DACs. To mitigate that effect, a dual switched-capacitor-resistor feedback DAC technique is proposed. The architecture has the additional benefit of reducing the typically high switched-capacitor-resistor DAC output peak currents, resulting in reduced slew-rate requirements for the loop-filter integrators. The feedback technique has been implemented with a third order, 3-bit delta-sigma modulator for a low power radio receiver, in a 65 nm CMOS process, where it occupies an area of 0.17 mm2. It achieves an SNDR of 70 dB over a 125 kHz bandwidth with an oversampling ratio of 16. The power consumption is 380 μW from a 900 mV supply.