NON-LINEAR MODEL OF THE SECOND ORDER VOLTAGE AND CURRENT SWITCHED CP-PLLS

E. ALI, G. MUSTAFA, K. B. AMUR, N. NIZAMANI, A. R. KHATRI, T. R. MEMON

Abstract


The charge-pump phase locked loop (CP-PLL) circuit is most suitable technique used to align the two signals in different applications in communication. The CP-PLL is mostly feasible because of its low cost, integerable and precise features. The chargepump produces an error current, which is then integrated by the following loop filter. The error current is constant if the charge-pump is based on constant current sources however the pump current varies in the case of voltage switched charge-pump (VSCP). The conventional gain of detecting unit is directly proportional to the error current. It behaves non-constantly when the voltage switched charge pump (VSCP) structure is used. Hence, the pump current applied to the loop filter (LF) is no more constant. This latent  peculiarity in the form of non-constant pump current delivered from the VSCP influences the system dynamic. In this paper, it is focused on comparing the transient dynamics of the second order CP-PLL system considering the current output of the both chargepump circuits. The simulation results are achieved using discrete time non-linear event driven model considering the balanced and unbalanced pump current situations.

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