20-MHz bandwidth continuous-time delta-sigma modulator for EPWM transmitter

Abstract

A 1.5-bit 20-MHz bandwidth continuous-time delta-sigma modulator (CT-DSM), which is suitable for envelope pulse-width modulation (EPWM) transmitters, is presented. To compensate the process-voltage-temperature variation, a resistor calibration method is proposed. The proposed calibration scheme improves a signal-to-quantization-noise-ratio (SQNR) by 18%. The switched capacitor digital-to-analog converter (DAC) and tri-level output DAC are adopted to improve non-ideal effects and implement multi-level encoding, respectively. Over 44 dB SQNR has been achieved for all corner simulation condition with an oversampling ratio of 13.056 and 20-MHz of bandwidth. The power consumption of the modulator is 11.6 mW from the 1.08 V supply. 1.74% of error vector magnitude can be obtained for a 20 MHz LTE signal with a 9.7 dB peak-to-average power ratio.