Research On High Speed Frequency Synthesizer Based On Voltage Preset

Frequency synthesizer as the generation unit of refer clock and local signal, is one of the extremely important constituent part for the modern electronic communications systems and equipment. With the rapid development of modern electronic communication technology, frequency source with higher performance is required. In the satellite communication and radar systems, broad band fast hop frequency synthesizers plays a more and more important role, the fast hop frequency synthesizer technology has drawn much more attention. Among of the numerous implementation scheme, the fast hop frequency source based on PLL owes lots of advantages, such as broad signal band, simple circuit architecture, low power consumption and phase noise, excellent spurious suppression. For those features, the study work of fast hop frequency synthesizer technology based on PLL makes a great sense.This article proposes a broad band fast hop frequency synthesizer theory using the voltage preset method which based on PLL, on the basis of the traditional phase locked loop module, adding a peripheral auxiliary locking circuit, presetting the coarse voltage to the Vtune of VCO, to short the frequency switching lock time; every time the frequency changes, the system controller FPGA conducts high speed control, downloading coarse voltage control words, then the digital to analog converter output the analog coarse voltage to the adder consisting of the operational amplifier, tune the voltage controlled oscillator(VCO) to get the wanted frequency signal by cooperating with the integral voltage of charge pump through the loop filter, which can realize a broad range frequency hop, the lock time can be shorten to about 20uS with perfect spurious suppression, phase noise etc.In the paper, the development history of frequency synthesizers is introduced at first, and then focus on analysis of PLL frequency synthesizer working principle, constituent structure and mathematical model. On this basis, several fast hop frequency synthesizer scheme are introduced and shared further, and compared their own performance with each other. According to the performance requirement of subject, the scheme for the broad band fast hop frequency source is decided at last. In the follow chapter, the design of loop filter is discussed in detail, including the derivation of loop transfer equation and the theory of loop bandwidth and phase angle margin. At the same time, using some related software like ADS etc, to build module and carry out the simulation. Finally the circuit is manufactured to verify the feasibility of the design.