Programmable Delay Line Based High-speed PPM Modulator with 50 ps Time Resolution

Abstract

Energy efficiency is an important metric by which modern communications systems are evaluated. Pulse position modulation (PPM), which uses time intervals among pulses to encode the transmitted data, provides unlimited energy-saving opportunities at the cost of spectrum occupancy. Considering this excellent property, PPM is gaining attention as a candidate waveform for the next generation of long-distance and space communications, where energy efficiency and peak signal-to-noise ratio are the key factors. This paper is devoted to implementing and evaluating a high-speed transmitted reference pulse-position modulation (TR-PPM) modulator board that employs a digital-to-time converter (DTC) based on high-accuracy programmable delay line integrated circuits. The developed prototype can generate high-order TR-PPM signals with up to 256 pulse positions, having a time resolution of 40 ps. Using step recovery diodes (SRDs) at the front-end of the modulator allows for achieving a pulse duration of about 150 ps. The testing of the developed prototype has shown that the board can generate TR-PPM waveform with high accuracy and allows achieving data rates up to 20 Mbit/s.