Relaxing all-digital transmitter filtering requirements through improved PWM waveforms

This paper presents a new pulse-width modulation (PWM) technique for all-digital transmitters (ADT) that reduces the PWM harmonic distortion near the transmitted carrier frequency. This technique is used to shape the ADT's quantization noise by changing the PWM waveform patterns, avoiding the need of a high quality factor analog output filter. With this approach, the ADT gains an additional degree of flexibility for the carrier frequency since it is not bound to any fixed narrow-band filter. The results show the feasibility and advantages of the approach without increasing the complexity for the overall system. The noise peak power reduction shown is quite significant, reaching more than 50 dB reduction for the first PWM harmonic.