A Scalable Bandwidth Mismatch Calibration Technique for Time-Interleaved ADCs

Abstract

This paper presents a foreground calibration method for both a sampler and a track-and-hold (T/H) buffer bandwidth mismatch in highly time-interleaved analog-to-digital converters (TI-ADCs). The T/H buffer bandwidth mismatch stems from the length difference of interconnect lines between the buffer and the channel ADC, while the sampler bandwidth mismatch arises from the mismatch in a switch and a sampling capacitor. To address both mismatches along with other mismatches residing in TI-ADCs, this papers utilizes least-squares (LS) minimization technique in order to extract mismatch parameters while injecting a sinewave at two distinct frequencies. Programmable capacitor arrays (PCAs) are used to tune the bandwidth of sampler, and correcting buffer bandwidth mismatch is performed in digital-domain. The method presented here is scalable to arbitrary number of interleaved paths, and can easily be combined with existing calibration methods for gain, offset, and timing-skew mismatches. Numerical experiment via Monte-Carlo simulations demonstrates significant performance improvement in the spurious-free dynamic range (SFDR) from 38 dB to 75 dB for a 32-channel time-interleaved ADC model that includes all major mismatches.