Suppression of Quantization Noise for EPWM Transmitter with 2nd-Order Delta-Sigma Modulator

Multicarrier modulation schemes such as orthogonal frequency division multiplexing (OFDM) requires linearity for power amplifiers (PAs), which results in low power efficiency operation of PAs. In order to mitigate the issue, envelope pulse-width modulation (EPWM) transmitter has been proposed that employs a A-O modulator to convert envelop of the high PAPR signal into pulse-width modulation (PWM) waveform. However, quantization noise from the A-O modulator is added on the output signal and causes outband spurious radiation. In this paper, the effect of quantization noise suppression for EPWM transmitter with the 2nd-order A-O modulator is revealed. The employed noise suppression method adds small amplitude perturbation to the phase modulator output in order to cancel quantization noise close to the carrier frequency. The cancelation effect can be maximized by using the 2nd-order A-O modulator with a null-response frequency. It improves adjacent and the next-adjacent channel leakage power ratios (ACLR and Next-ACLR) dramatically without any narrowband bandpass filter. The simulated results show that the ACLR and the Next-ACLR are improved by 12 dB and 20 dB, respectively.