Based On The Phase Modulation Technology Research Of Sigma - Delta Method

In modern wireless communication, a kind of high efficiency and linearity transmitter is required to support the multi-mode, multi-band technologies. The polar transmitter is the best candidate theoretically. The increasing of data rate and bandwidth of phase signal demands the transmitter provides better phase modulation performance. The modulator based PLL not only can be used to produce GSM signals, can also be applied for phase modulation in polar transmitter, so it has been widely studied in phase modulation.On the basis of the modulator based PLL, and from the perspective of improving the maximum data rate, this dissertation delves into the phase modulation technique based Sigma-Delta method. It mainly involves:1. According to the actual demand, the combination of Sigma-Delta modulator and PLL is chosen as research direction. The feasibility of the design is demonstrated through the investigation of the Sigma-Delta modulation and Sigma-Delta fractional-N PLL.2. Aiming at the design method of phase modulator based Sigma-Delta PLL for constant envelop modulation signal. The relationship between phase modulation performance and Sigma-Delta PLL loop parameters is analyzed in details. And the maximum data rate is defined to be affected by the PLL loop bandwidth.3. For solving the problem that contradiction exists between data rate and loop bandwidth, compensated filter is applied to pre-compensate the phase signals and balance the suppression beyond loop bandwidth. The modulation performance of this method is detailed, proving that the data transfer rate can be improved. The applicable condition of compensated filter is also proposed.4. To avoid the problem that bandwidth constraint is inevitable in closed-loop modulator, phase modulator based sigma-delta phase rotator is investigated to increase the data rate. The modulation principle and noise analysis of this structure is detailed. The design is implemented in FPGA and the modulation performance is tested.The simulation reveals that the phase modulator based sigma-delta phase rotator can effectively achieve phase modulation, and the relative bandwidth reaches3.95%which indicates that this structure is more potential to wideband phase modulation than conventional modulator.