Oversampled pipeline A/D converters with mismatch shaping

Abstract

This paper presents a pipeline analog-to-digital converter (ADC) with improved linearity. The linearity improvement is achieved through a combination of oversampling and mismatch shaping, which modulates the distortion energy out of band. Mismatch shaping can be realized in a traditional 1-bit/stage pipeline ADC, but the ADCs transfer characteristic properties limit its effectiveness at pushing the distortion out of band. These limitations can be alleviated by using a 1-bit/stage commutative feedback capacitor switching pipeline design. A test chip was fabricated in a 0.35-/spl mu/m CMOS process to demonstrate mismatch shaping. Experimental results obtained indicate that the spurious-free dynamic range improves by 8.5 dB to 76 dB when mismatch shaping is used at an oversampling ratio of 4 and a sampling rate of 61 MHz. The signal-to-noise and distortion ratio improves by 3 dB and the maximum integral nonlinearity decreases from 1.8 to 0.6 LSB at the 12-bit level.