28.2 An 11.4mW 80.4dB-SNDR 15MHz-BW CT delta-sigma modulator using 6b double-noise-shaped quantizer

Quantizers are key building blocks in both continuous-time (CT) and discrete-time (DT) delta-sigma modulators (DSMs). Among various types of quantizers, noise-shaping quantizers such as VCO-based quantizers and noise-shaped integrating quantizers (NSIQ) [1] are attractive solutions since they provide an additional order of quantization noise shaping. On one hand, VCO-based quantizers are relatively fast, but are often non-linear. On the other hand, NSIQs suffer from a tradeoff between the counting clock speed and resolution, but can be very linear. Nevertheless, the NSIQ offers an interesting benefit that the quantization error is inherently available in both time and voltage domains. Thus, the NSIQ can be easily extended to provide an additional order of noise shaping. In this paper, we propose a double noise-shaping quantizer (DNSQ) incorporating an NSIQ and a gated-ring-oscillator-based (GRO-based) quantizer [2] that not only provides 6b quantization levels with a back-end digital integrator [3], but also offers two extra orders of noise-shaping.