A 4th order continuous-time [Delta] [Epsilon] ADC with VCO-based integrator and quantizer

Abstract

The use of a VCO-based integrator and quantizer within a continuous-time (CT) [Delta] [Epsilon] analog-to-digital converter (ADC) structure is explored, and a custom prototype in a 0.13 [mu]m CMOS with a measured performance of 81.2/78.1 dB SNR/SNDR over a 20 MHz bandwidth while consuming 87 mW from a 1.5V supply and occupying an active area of 0.45 mm2 demonstrated. A key innovation is the explicit use of the oscillator's output phase to avoid the signal distortion that had severely limited the performance of earlier VCO-based ADC's, which exclusively made use of the output frequency. Furthermore, the proposed architecture includes a scheme for performing fast dynamic element matching (DEM), enabling first-order shaping of unit-element mismatch in all feedback DAC's.