VCO-Based 0-\(\varDelta \varSigma \) MASH ADC
As discussed in Chap. 4, to address the issue of limited voltage headroom and to take advantage of the reduced CMOS gate delay in scaled CMOS technologies, VCO-based highly-digital ADCs have recently emerged in recent years. However, the performance of VCO-based ADCs is limited by the inherent nonlinearity of the VCOs. As shown in Fig. 7.1, a VCO-based ADC can be utilized as a quantizer in a single-loop \(\varDelta \varSigma \) modulator. The preceding loop filter suppresses both the quantization noise and the nonlinearity, however, a high loop gain results in a high power consumption and potential instability problems. As discussed in Chap. 3, in traditional \(\varDelta \varSigma \) ADC design, compared to single-loop structures, MASH architectures can offer a higher-order noise shaping with less instability concerns. This structure can also be implemented with VCO-based quantizers as will be demonstrated.
- 1.P. Zhu, X. Xing, G. Gielen, A 40MHz-BW 35fJ/step-FoM nonlinearity-cancelling two-step ADC with dual-input VCO-based quantizer, in IEEE European Solid-State Circuits Conference (ESSCIRC), 2014, (Venice, Italy, 2014), pp. 63–66Google Scholar
- 3.A. Gharbiya, D.A. Johns, A 12-bit 3.125 MHz bandwidth 0–3 MASH Delta-Sigma modulator. Solid-State Circuits, IEEE J. 44(7), 2010–2018 (2009)Google Scholar
- 4.Y. Dong, R. Schreier, W. Yang, S. Korrapati, A. Sheikholeslami, A 235 mw CT 0–3 MASH ADC achieving \(-67\) dbBFS/Hz NSD with 53 MHz BW, in Solid-State Circuits Conference Digest of Technical Papers (ISSCC), 2014 IEEE International, (IEEE, 2014), pp. 480–481Google Scholar
- 5.A. Sanyal, K. Ragab, L. Chen, T. Viswanathan, S. Yan, and N. Sun, A hybrid SAR-VCO Delta-Sigma ADC with first-order noise shaping, in 2011 IEEE Symposium on CICC, (2014), pp. 1–4Google Scholar
- 7.K. Reddy, S. Rao, R. Inti, B. Young, A. Elshazly, M. Talegaonkar, P.K. Hanumolu, A 16-mW 78-dB SNDR 10-MHz BW CT \(\Delta \Sigma \) ADC using residue-cancelling VCO-based quantizer. Solid-State Circuits, IEEE J. 47(12), 2916–2927 (2012)Google Scholar
- 9.W. Yu, J. Kim, K. Kin, S. Cho, A time-domain higher-order MASH Delta-Sigma ADC using voltage-controlled gated-ring oscillator. IEEE Trans. Circuits Syst. I: Regul. Pap. 59(8), 856–866 (2012)Google Scholar