Linearity enhancement techniques in low OSR, high clock rate multi-bit continuous-time sigma-delta modulators

This paper evaluates two techniques to improve the linearity of the main feedback D/A converter in multi-bit continuous-time sigma-delta modulators (CT-SDM). A self-calibrated current-steering (SCCS) implementation of the D/A converter is compared to the usage of a data-weighted averaging (DWA) algorithm on the selection of uncalibrated D/A-elements. Two test-chips including the two different solutions are presented and measurement results are compared. Clocked at 300 MHz, the two CT-SDMs achieve a dynamic range of 67 dB (DWA) and 70 dB (SCCS), respectively, over an analog bandwidth of 15 MHz.