Design Of Wideband Phase Lock Loop Filter

The Loop Filter, being the important part of any PLL based frequency synthesizer, its performance determines to a large extent that of the whole synthesizer . Due to the most important and demanding parameters of the VCO tuning voltage's purity, we use Loop Filter to maintain the stability of the PLL, balance the noise of PLL inband and outband, prevent the voltage jump of the VCO tuning voltage and the spurs suppression of the PLL et. Therefore, the design of the LPF become the key of many PLL applications.The wideband PLL loop filter designed in this thesis is used in an ASIC for digital TV tuner. The chip converts the wide spectrum of TV signals to a fixed middle frequency ,about 36MHz , The wideband PLL loop filter designed in this thesis must be well applicable in quite wide tuning range and high performance.Because the resonance network of the VCO is off chip, that demand the LPF can amplify the tuning voltage of the VCO from 3.3V to 33V, we must design an active LPF. This paper designs an active LPF amplifies the DC voltage with an NPN transistor. It keeps the stability of the PLL loop and the bandwidth of it is optimized to improve the noise of the PLL.This paper discuss the foundation knowledge of the design of the LPF, the PLL abstract model, the relation of the LPF parameter with the PLL Open-Loop bandwith, phase margin, phase noise and the Spurs suppression. Then calculate the circuit parameter with the model, simulation and test also. At last, the LPF designed is validated in the usage of the Tuner appliance system.