Design Of Baseband Circuit Based On RF Front-End Of GPS

With the development of communication, navigation, computer and semiconductor integration technologies; more and more GPS receivers are embedded into communication systems, computers, security and consuming electronics products. CMOS integrated GPS receivers with low power and low cost is getting more and more attention, and has become one of the RFIC research interests. In the RF front-end architecture of GPS receiver, baseband circuits i.e. filter and automatic gain control (AGC) are the most important modules, which play a role as selecting the frequency, changing the system gain of the system and adjusting the power of each level signal.In the dissertation, the main contents are as follows:Firstly, a transconductance amplifier using source-coupled resistance to change the linearity range and a highly-linear variable gain amplifier (VGA) with the new exponential gain characteristics are presented.Secondly, the design method of ubiquitous Gm-C filters is researched. Adopting the biquard architecture, a 4th-order Butterworth low pass filter is designed. And the designed filter has the advantages of simple architecture and tunable linearity.Thirdly, the basic concepts and operation principles of AGC are expressly analyzed. And an envelope detector is designed further the design of AGC circuit is achieved. Simulation results show that under low power voltage, the AGC has good voltage control range, wide bandwidth and high linearity.Finally, LPF and AGC are designed and simulated in TSMC 0.18μm CMOS process and the layout and post-simulations have been completed. Post-simulation results show that the whole circuits have good time domain and frequency domain responses, and are applicable for embedding in GPS receivers.