A Calibration Scheme for a Sigma-Delta Modulator Using Passive Integrators

This paper describes a calibration method for a 2-1 MASH $\Sigma\triangle$M using passive integrators. Due to process variations the RC product can vary, causing a degradation in circuit performance. Therefore, a circuit measuring the RC time constant and converting it into a digital coefficient, was designed. This coefficient is used to calibrate the reference voltage of the $\Sigma\triangle$M to decrease the variability of the feedback signal and to calibrate the digital cancellation logic (DCL), improving quantization noise cancellation. Electrical transient noise simulations results of the $\Sigma\triangle$M with calibration prove validity of the presented method showing performance improvement in worst corners.