High Speed Multi-Channel Optical Sampling Technique for Analog-to-Digital Converters

摘要

We describe the design and implementation of an eight channel optical sampling technique for analog-to-digital (A/D) converters. A single mode-locked laser source with a pulse repetition rate of 250 MHz is used to generate eight highly synchronized sampling clocks each running at 500 MHz. The basic sampling circuit consists of a reversed-biased photodiode which operates as a very fast optoelectronic switch. Actuating the photodiode ON and OFF with mode-locked laser pulses produce sampled RF signals. In the implementation of this A/D architecture, the optical clocks are delayed relative to each other using fixed passive delay lines. The time-shifted clock signals allow for sampling different phases of the input RF signal resulting in an aggregate sampling rate of 4 Gigasamples/sec (GSPS). We shall show the optical clock setup necessary in order to achieve a 4 GSPS rate. We shall also present sampling results for input RF signals with frequencies ranging from 10 to 500 . Interleaving of the sampled RF output from different sampling channels will also be demonstrated.