Design And Research On L₁-band Down-conversion Circuit Of GPS Receiver

Global Positioning System (GPS) is a new generation of satellite navigation and positioning system established by United States Department of Defense. Currently, GPS has been widely used in most military and civil fields which need navigation and positioning for its characteristics of high-precision, all-weather, global coverage, convenience, flexibility, inexpensive and high-quality. However, the GPS signal received by antenna has high frequency and weak power, so it is necessary to make corresponding signal processing for the purpose of normal GPS performance.Between the GPS receiver antenna and base-band signal processing unit, RF front-end circuit plays the main role in GPS signal's adjusting and down-conversion processing. Signal adjusting could filter the noise, interference outside of L1-band and amplify its power through band pass filter (BPF) and low noise amplifier (LNA). Meanwhile, frequency-down processing usually completed by down-conversion circuit, including the stages of mixer, AGC control, signal filtering and amplification.The main purpose is to convert the higher-frequency GPS signal into lower-frequency IF signal and make necessary filtering, gain control and noise suppress in this process.In this paper, the L1-band down-conversion circuit of GPS receiver is designed. First, the work principle of GPS receiver and down-conversion circuit is introduced, and the impact elements of various parts of this circuit is analyzed.Then the final design of this paper has been determined. The software and hardware have been combined together in this design. Software part is to write control procedures to ensure that the output of two local oscillator signals, and the hardware is mainly to design of mixer circuit, the oscillator circuit, automatic gain circuit and other modules. Finally, the entire circuit has been welded and tested. The result shows the designed down-conversion circuit can successfully convert 1575.42MHz GPS signal into 46.42MHz IF signal, have done a better signal filtering and amplification, and the output IF signal can meet the requirements of base-band signal processing.