A discrete phase-locked loop for undergraduate laboratories

Phase-locked loop (PLL) experiments in undergraduate instructional laboratories are usually designed around a monolithic IC chip. However, insight into circuit operation is mostly lost with use of the IC chip. In this paper, a PLL circuit consisting of only three transistors is presented. Given its simple topology, it can be realized with discrete components and requires minimal analysis. Hence, the presented circuit is ideally suited for demonstrating PLL principles in undergraduate laboratories