Simulation of a discrete PLL with variable parameters

The discrete phase lock loop (DPLL) proposed by G. S. Gill and S. C. Gupta [1] is simulated with a programmable calculator (TI-58). Many interesting properties of its behavior are easily shown such as the pulling-up time, the effects of varying the coefficients of the filter, and the effect of phase and frequency steps on the output. If the constant K1of the filter is initially made high, and its value decreases with time, it is possible to obtain a DPLL with large pull-in range and which is very insensitive to input noise.