For The Development Of Frequency Synthesis Source Of Acousto-optic Device

Acousto-optic devices are widely used in modern technology, such asacousto-optic signal processing and spectral analysis. The frequency synthesizer is anindispensable part of acousto-optic modulator, and it is designed in this dissertation. Toachieve a better performance, the DDS+PLL structure is adopted. The frequencysynthesizer is capable of FM, AM (DSB with carrier) and ASK modulation. In thisdissertation, several topics are carried out as following:1. Several frequency synthesizer technologies are discussed, as well as theadvantage and disadvantage. The way of implement is adopted according to thepractical consider.2. The hardware circuit of the frequency synthesizer is designed. The circuitincludes a DDS, PLL, RF switches, mixers, band-pass filter, variable gain amplifier andpower amplifier. In the designing process of phase-locked loop circuit, ADS is used tosimulate PLL phase noise performance. In the designing process of FM modulationADS is used as well to simulate the PLL FM performance. The spectrum of FM, AM,ASK modulation is analyzed.3. When designing the PCB board, some measures is taken to get good EMCperformance. To assure a pure power supply, de-coupling is adopted to decrease theripple of the power line; the routing of differential line is carefully designed; the designof the PLL part on the board is carefully considered to decrease Interference.4. The testing process and the result of the spectrum analyzer are offered, as well asanalysis of the spectrum.Output carrier frequency:325MHz-775MHz; frequency updatetime<1ms, phase noise:-70dBc/Hz@1kHz, FM baseband frequency>10kHz. In thisdesign, the spur spectrum of DDS or PLL comes from DAC nonlinear and sampling, orthe charge pump. Moreover, increase the charge pump current and phase detectorfrequency can improve phase noise effectively.