Design of low-power area-efficient continuous-time [delta-sigma] ADC using VCO-based integrators with intrinsic CLA
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In this thesis, the design of a scaling-friendly continuous-time closed-loop voltage controlled oscillator (VCO) based Delta-Sigma analog to digital converter (ADC) is introduced. It uses the VCO as both quantizer and integrator, and thus, obviates the need for power-hungry scaling-unfriendly operational transconductance amplifiers (OTAs) and precision comparators. It arranges two VCOs in a pseudo-differential manner, which cancels out even-order distortions. More importantly, it brings an intrinsic clocked averaging (CLA) capability that automatically addresses digital to analog converter (DAC) mismatches. The prototype ADC in 130 nm complementary metal-oxide-semiconductor (CMOS) occupies a small area of 0.03 mm² and achieves 66.5 dB signal to noise and distortion ratio (SNDR) over 2 MHz bandwidth (BW) while sampling at 300 MHz and consuming 1.8 mW under a 1.2 V power supply. It can also operate with a low analog supply of 0.7 V and achieves 65.8 dB SNDR while consuming 1.1 mW. The corresponding figure-of-merits (FOMs) for the two cases are 0.25 pJ/conversion-step and 0.17 pJ/conversion-step, respectively.