Analysis of Deadbeat Control for an Integer-N Charge-pump PLL

The conventional method to decrease the settling time of oscillators is to increase the bandwidth, which in turn results in an increase in the spur content, affecting the transient performance of the PLL. Even though several architectural variations have been suggested to reduce the lock time, a novel method to reduce the settling time is “Deadbeat control”, in which an additional system is implemented in feedback with the PLL. This method accomplishes the reduced settling time without any change in the design of the forward gain components. Before the implementation of the deadbeat control, the concepts of controllability and observability have to be satisfied for the PLL. In this particular work, these tests are carried out on an integer-N charge-pump PLL, and then the deadbeat control is verified. The settling time and the overshoot are deduced from the step-response of the PLL, by means of MATLAB simulation.