A 3-Order Multi-Level Complex Delta-Sigma Modulator For Switched-Mode Power Amplifier

Bitstream transmitter requires the RF input signal to become the pulse train which is typically utilized delta-sigma-like modulation. This paper proposes a modified 3-order complex delta-sigma modulation (CDSM) structure which contains a 3-level quantizer. The particle swarm optimization (PSO) algorithm is employed to optimize coefficients of the structure. Using the proposed CDSM technique reduces the quantization noise significantly at the output of the modulator. Various forms of signals are utilized to validate the proposed structure. For a Long-Term Evolution (LTE) signal with 20 MHz bandwidth and 10 dB peak-to-average power ratio, it achieves the adjacent channel leakage ratio (ACLR) of 46.73dB. The comparison study between envelope DSM and the proposed CDSM shows 24.35dB improvement in ACLR of the LTE signal. The results for LTE signals are able to pass the spectral requirements defined by the standard without applying predistortion techniques. By comparing error vector magnitude (EVM) of output signals with different filter bandwidth, the proposed CDSM loosens the requirements for post-stage filters.