A Dual-Phase Center-Aligned 7-Bit Digital Pulsewidth Modulator for Polar Transmitters

This article presents a dual-phase center-aligned 7-bit digital pulsewidth modulator for the envelope modulation of pulse-modulated polar transmitters (PMPTs). The digital pulsewidth modulator operates at a clock frequency and delivers the modulation frequency of 100 MHz. A delay-locked loop (DLL) consisting of 128 delay cells is used to generate the pulse edges for synthesis of center-aligned pulsewidth modulation (PWM) waveforms. The pulsewidth resolution is 78.1 ps. The measurement results show that the integral nonlinearity (INL) and differential nonlinearity (DNL) of the output pulses are within ±0.4 and ±0.3 LSB, respectively, in the duty cycle range of 2.12%-96.51%. Tested with a 20-MHz 256-quadrature-amplitude modulation (QAM) 5G new radio (NR) signal, the transmitter signal using the output of the modulator achieves the adjacent channel leakage ratio (ACLR) of -33.8 dBc.