A concurrent triple-band digital transmitter using feedforward noise cancellation for delta-sigma modulation

A concurrent triple-band digital transmitter architecture with relaxed RF output filter requirement is presented in this paper. With non-contiguous inter-band carrier aggregation, all digital transmitters based on delta-sigma modulation and pulse-width modulation have suffered from out-of-band noise and spurious tones, requiring extremely demanding RF output filter design. We demonstrate a feedforward noise cancellation technique in order to suppress the out-of-band quantization noise of concurrent triple-band delta-sigma modulation for the first time. An experimental prototype based on an asymmetric RF power combiner and a 5-bit 7-GS/s DAC for noise cancellation realizes concurrent triple-band transmission of LTE Advanced signals, which consist of 710 MHz, 1750 MHz, and 2510 MHz bands with 30-MHz aggregated total bandwidth. The prototype achieves better than 42-dB spurious-free dynamic range (SFDR) and -47-dBc adjacent channel power ratio (ACPR), enabled by up to 12-dB out-of-band noise suppression.