A Generic Foreground Calibration Algorithm For ADCs with Nonlinear Impairments

Abstract

This paper presents a generic foreground calibration algorithm which compensates for memoryless nonlinear impairments in pipeline, SAR or hybrid ADC architectures. Amplifier nonlinearity, comparator offsets, capacitance mismatch and settling time errors are considered. During the calibration process, each element of a look up table is computed by mapping each raw ADC output value to an estimate of the corresponding input, and the most likely input corresponding to each raw ADC output is computed and stored in the table; this table is then used during normal operation to map the raw values to the calibrated ADC outputs. Complexity reduction techniques are presented to facilitate an in-circuit hardware implementation in order to reduce foreground calibration time. The algorithm's performance is evaluated using a SAR ADC model suffering from various nonlinear impairments. Results are presented for settling time errors, capacitor mismatch scenarios, and a wide range of nonlinear amplifier parameters, demonstrating a significant performance improvement in all cases.

A Generic Foreground Calibration Algorithm For ADCs With Nonlinear Impairments

“…The averaging in (8) produces an updatedψ every K samples, allowing tracking of any small changes to the input. After obtaining the firstψ, both stages (described in Subsections II-A and II-B) can run in parallel to estimate the input voltagẽ v in [k], which is used to update the LUT content as shown in 8) and ( 9), modified from [24].…”

“…is the inverse of the Gaussian cumulative distribution function (CDF). Since M is relatively large, we can assume that max m (τ m ) and − min m (τ m ) are independent, and hence by (24),τ max has a Gamma distribution with position parameter c g , shape parameter 2 k g and scale parameter θ g /2;…”

“…Here, the same ADC configurations are used to form a TIADC system with M = 8 sub-ADCs and aggregated Fig. 13: Measured ENOB with varying S/H nonlinearity coefficients, modified from [24].…”

“…Fig.9: ENOB distribution for SAR ADC with (a) linear combination using ideal weights, (b) without calibration, and (c) proposed calibration algorithm, modified from[24].…”

Effective extraction method for triple errors in foreground calibration of TI‐ADCs

“…There are many state-of-the-art structures for the foreground calibration of TI-ADCs where each scheme has its benefits and drawbacks. [13][14][15][16][17][18] However, a thorough analysis depicts that the complicated hardware for the calibration of timing skew is the common drawback of these systems. Besides, the need for a general-purpose calibration algorithm for the triple errors becomes vital, knowing that each type of ADC structure suffers from an error more than the other mismatches.…”