A 20mW 61dB SNDR (60MHz BW) 1b 3rd-order continuous-time delta-sigma modulator clocked at 6GHz in 45nm CMOS

Continuous-Time ΔΣ Modulators are a popular architecture choice for ADCs in deep-submicron processes [1-4]. The maximum sampling rate is set by Excess Loop Delay (ELD) considerations. ELD comprises the comparator latency, feedback DAC delay (DEM delay etc.) and any additional delay due to parasitics. For a wideband 1b modulator clocking at high speeds (multi-GHz), the key challenge is modulator stability due to large ELD set by comparator speed limitations and integrator parasitic poles. This paper describes circuit techniques to minimize ELD and a compensation scheme that ensures modulator stability given a 1-clock-period ELD. These techniques have enabled the design of a 3rd-order 1b modulator clocked at 6GHz in 45nm CMOS.

[1]  C. Holuigue,et al.  A 14b 20mW 640MHz CMOS CT /spl Delta//spl Sigma/ ADC with 20MHz Signal Bandwidth and 12b ENOB , 2006, 2006 IEEE International Solid State Circuits Conference - Digest of Technical Papers.

[2]  Venkatesh Srinivasan,et al.  A 1.16mW 69dB SNR (1.2MHz BW) continuous time £Δ ADC with immunity to clock jitter , 2010, IEEE Custom Integrated Circuits Conference 2010.

[3]  O. Oliaei,et al.  Sigma-delta modulator with spectrally shaped feedback , 2003, IEEE Trans. Circuits Syst. II Express Briefs.

[4]  Peng Gao,et al.  A 2.8-to-8.5mW GSM/bluetooth/UMTS/DVB-H/WLAN fully reconfigurable CTΔΣ with 200kHz to 20MHz BW for 4G radios in 90nm digital CMOS , 2010, 2010 Symposium on VLSI Circuits.

[5]  Min C. Park,et al.  A 0.13µm CMOS 78dB SNDR 87mW 20MHz BW CT ΔΣ ADC with VCO-based integrator and quantizer , 2009, 2009 IEEE International Solid-State Circuits Conference - Digest of Technical Papers.

[6]  Kofi A. A. Makinwa,et al.  A 4GHz CT ΔΣ ADC with 70dB DR and −74dBFS THD in 125MHz BW , 2011, 2011 IEEE International Solid-State Circuits Conference.

[7]  Nagendra Krishnapura,et al.  Compensating for Quantizer Delay in Excess of One Clock Cycle in Continuous-Time $\Delta\Sigma$ Modulators , 2010, IEEE Transactions on Circuits and Systems II: Express Briefs.