To study the principle of PPM modulation and demodulation, we design two kinds of PPM modulation and demodulation systems. In demodulation, system A first detects all edges information of PPM signal and outputs a flag pulse at the edge time; then, based on this pulse, system A will reverse outputs in turn and gets the demodulation signal. With system B, a correction module is added based on system A to reduce the requirements for the transmitter end. The principle for system B goes like this: when the first edge signal arrives, it judges whether it is the rising edge or the falling edge; if it is a rising edge, it maintains the outputs of system A; if it is a falling edge, then it outputs the reversed outputs of system A. The experimental results show that the two kinds of modulation and demodulation systems designed in this paper can modulate and demodulate the input data under the clock of 50MHz. And because of the addition of correction module, system B’s total power consumption is 0.13mw higher, and it occupies 2 more logic units than system A does. However, system B can reduce the requirements for the transmitter end compared with system A.