A wideband sigma-delta PLL based phase modulator with pre-distortion filter

A wideband sigma-delta PLL based phase modulator is presented in this paper. In the proposed architecture a pre-distortion filter is applied to balance the phase signals, compensating the suppression beyond the loop bandwidth. By properly balancing the PLL transmission characteristics, the data rate limitation is relieved to the sigma-delta PLL bandwidth. The applicable condition of pre-distortion filter is also analyzed in this paper. The simulation results show that with PLL bandwidth of 1MHz the maximum phase error is no more than 10° and that RMS error is only 0.06° when transmitting 2.85 Mbps GMSK signals.