A 24-kHz third-order continuous-time delta-sigma modulator using passive LPF

A continuous-time Delta-Sigma modulator (CTDSM) using passive low pass-filter (LPF) in the feedback DAC is proposed. The LPF helps to reduce the signal swing and slew-rate requirements of the first amplifier in CTDSM and also contributes one-order noise shaping. A modulator synthesis is analyzed. The performance of the modulator has been verified through simulations using a standard 0.18-μm CMOS process. It achieves 77.48-dB SNDR at 6.144-MS/s sampling rate and consumes 32.4-μW power.