Analysis of SettlingTime in Charge Pump Phase-Locked loops regarding Non-ideal Effect

Phase locked loops (PLL) are widely used in telecommunication systems. Frequency characteristics and settling time are the two most important features of PLLs. In phase lock loops, several nonlinear factors can be considered, one of which is the nonlinear behavior of the phase detector. In fact, load pump phase locking loops (CPPLL) are nonlinear systems due to the nonlinear behavior generated by the load pump. Although the applied current is fixed in an ideal load pump, this is not fixed in practice because of the non-ideal behavior of the transistors. In this paper, considering the channel length modulation (CLM) effect caused by the drain-source voltage of MOSFET transistor, a more accurate model is presented for the phase detector. By investigating the non-linear differential equation dominating the system and using the step-response approximation for the transient time analysis, new equations are obtained for the settling time and overshooting. In order to check the validity of the specified non-linear equations, the simulation was conducted in MATLAB Simulink. Moreover, in order to better assess the proposed method, the performance of a PLL subjected to the transistor’s drain-source voltage has been simulated and the effect of the different loop parameters, such as the loop’s resistor and current has been investigated. The final results showed the appropriate accordance of the analytical equations with the simulation results.