A 2nd-order sigma-delta mismatch-shaping current-steering DAC for zigbee transmitters

摘要

A low-power mismatch-tolerant current-steering digital-to-analog converter (DAC) was presented in this paper for ZigBee transmitter applications. Mismatches among the current units induce harmonic distortions and random analog noise which severely limit the linearity and resolution of the converter. 1st-order and 2nd-order sigma-delta dynamic element matching (DEM) schemes and the corresponding elements selection patterns were introduced in this paper, and the later was then applied to the DAC to spectrally shape the mismatches of the DAC without adding complex digital hardware. Measurement results showed that the proposed 2nd-order DEM improved the resolution of the DAC from 4.5-bit to 11.4-bit, DNL from a maximum of 0.6 to 0.04LSB and INL from 1.1 to 0.07LSB. The SFDR, SNR and ENOB were respectively 70 dB, 58 dB and 7.3-bit for a 50 kHz@-6dBFS input signal.