Key Techniques Of Tdd Communication System Of The Receiver

We use the TDD system structure. This structure needs RF switches to change states between "transmitting" and "receiving". To solve the isolation problem we use several RF switches in series connection on the main signal path and also make good plan for PCB and cavity designs. So we need two such systems to buid up a communication relationship, and they work in the half-duplex way.To ensure a certain level of S/N at the input of the ADC, we try to suppress the NF of the whole receiver link to less than5.5dB. Because the power at the receiver input fluctuates, we need an AGC part in IF stage to ensure the adequate signal level to be demodulated, and we also add a function of RSSI indicator to indicate whether the receiving power is under control. To ensure the high speed data is responsed in time, we need compromise between response speed and BER on AGC design. For the purpose of coherent demodulation, we use the direct frequency domain method to do the carrier synchronous for QPSK modulation.At the beginning of this dissertation we try to investigate some key techniques which have ever played important roles in the development of the wireless receiver technology. And then we introduce some new ideas and system modules which have been published in recent years. After that, the author try to discuss the main design problems according to a practical project requirement, and then give a feasible solution on the practical circuit design.These would be done in several chapters.Two switches in serial in the receiver provide enough isolation which is more than90dB. Noise figure from the millimeter wave front end to the first IF stage at2.178GHz is about5.1dB;The communication BW is120MHz;AGC module provides34dB gain adjustment range,and this module also provides functions such as working mode selection,RSSI,etc. AGC response time is alse investegated.The phase noise of the LO produced by the carrier synchronization module is about-99dBc/Hz@10kHz when the signal occupied about74MHz BW is IQ modulated.