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设计了一种适用于多带VCO锁相环频率合成器的自动选带结构。使用迟滞比较器对VCO控制电压进行电平信息采集,并将信息输入到控制电路。控制电路根据接收到的电平信息完成状态跳变,并输出相应的选带开关控制电平,完成自动选带。基于Chartered公司0.18μm RF CMOS工艺完成电路设计,并应用于锁相环小数频率合成器。仿真结果表明,自动选带电路可正常工作,频率合成器能够在30μs内实现快速锁定。
An automatic tape selection structure for multi-band VCO PLL frequency synthesizer is designed. The hysteresis comparator is used to collect the level information of the VCO control voltage and input the information into the control circuit. The control circuit completes the status transition according to the received level information and outputs the corresponding control level of the selected switch with the completion of automatic selection. Based on Chartered Corporation 0.18μm RF CMOS process to complete the circuit design, and used in PLL fractional frequency synthesizer. The simulation results show that the automatic band selection circuit can work normally and the frequency synthesizer can realize fast locking within 30μs.