A 4th-Order Continuous-Time Delta-Sigma Modulator With Hybrid Noise-Coupling

A hybrid noise-coupling (HNC) technique is proposed to mitigate the issues with a digital noise-coupling (DNC) structure. In the proposed technique, the unwanted quantization noise that is generated from the noise-coupling analog-to-digital converter (ADC) is injected into the input of the quantizer with one-clock cycle delay, thus increasing the order of noise-shaping of this error. Behavioral simulation shows that the HNC is highly robust against gain variation. The proposed fourth-order continuous-time (CT) delta-sigma modulator (DSM) with HNC scheme was designed in a 28-nm CMOS technology with a core size of 0.3mm(2). With an oversampling ratio (OSR) of 32, the proposed design achieves a signal-to-noise-distortion ratio (SNDR) of 97.20-dB at a signal bandwidth of 15.625-kHz, which has a 7-dB improvement in comparison to DNC only without introducing significant hardware complexity.