A 4th-Order Continuous-Time Delta-Sigma Modulator Using 6-bit Double Noise-Shaped Quantizer

Abstract

This paper presents a continuous-time delta-sigma modulator using a double noise-shaped quantizer (DNSQ), which not only provides 2nd-order noise shaping but also generates a 6-bit quantization in the modulator. The proposed DNSQ efficiently extracts the quantization error in the time domain from a noise-shaped integrating quantizer (NSIQ), and directly applies it to a gated ring oscillator-based quantizer, hence achieving a 2nd order of noise shaping on its own. By incorporating the DNSQ, the modulator can achieve 4th-order noise shaping with only a 2nd-order loop filter. The proposed modulator is fabricated in a 0.13- $\mu \text{m}$ CMOS process with an active area of 0.17 mm2. It operates at 640 MHz and achieves a peak SNDR of 80.4 dB in a 15-MHz bandwidth while consuming 11.4 mW from a 1.2-V power supply.