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VCO Overload and Frequency Excursions: A non-linear Phenomenon in 2nd order Mixed Signal PLLs


Ehsan Ali, Nasreen Nizamani, Abdul Sattar Saand, Abdul Rafay Khatri, Ghulam Mustafa Bhutto


Vol. 17  No. 11  pp. 131-135


The Charge Pump Phase Locked Loop (CP-PLL) are widelys used component in modern day highly integrated electronic systems involved in wireless communication and smart system applications to perform several functions like frequency synhesis, clock recovery, and clock generation. The CP-PLL is switching device becuase of the triggering nature of the digital phase detector. Mostly a second order CP-PLL is utilized in comsumer electronics applications. The voltage controlled oscillator (VCO) generates signal with frequency excursion due to a non-linear effect, called jump frequencies arising due to the filter impedance. These jump frequencies may lead to overload the VCO. This paper highlights the overload situation of the two different architecture of mixed-signal PLLs. The simulations are performed using fast and efficient Event Driven (ED) model. The effect of jump frequencies on both architectures of the CP-PLL is analyzed.


Phase locked loop, VCO, Overload, non-linear system, frequency jumps.