RX-Band Noise Reduction in All-Digital Transmitters With Configurable Spectral Shaping of Quantization and Mismatch Errors

This paper describes the first purely digital approach to reduce the receive band noise in digitally-intensive RF transmitters. The proposed solution applies bandpass delta-sigma modulation and dynamic element matching (DEM) to the receive band (RX-band) instead of the transmit band. This enables selective attenuation of the noise originating from amplitude quantization and static mismatches of the digital-to-analog converter (DAC), which would otherwise reach the transmitter output almost unattenuated. A highly configurable 4th-order noise transfer function is designed to achieve optimum attenuation in the programmable RX-band, while ensuring negligible degradation of the transmitted signal quality as well as stable operation of the tree structure DEM encoder. A general validation of DEM, independent from the duration of the DAC impulse response, is also presented. The proposed solution is verified through system-level simulations with LTE signals. In the presence of typical amplitude and timing mismatches, the RX-band noise can be reduced below -160 dBc/Hz without filtering after the DAC, thus potentially enabling SAW-less operation of all-digital transmitters.