An Optical Flash Analog to Digital Converter

Abstract

Fast analog-to-digital (A/D) converters are important in a number of applications. Several systems have been proposed for fast A/D converters using optical technology1-4. The most common types of converters are the successive approximation and Flash converters. In a Flash converter there is a separate comparator for each possible output bit code. Each comparator is biased with a reference level that is a specific increment of the full scale value. Since comparators in a Flash converter operate in parallel, this architecture is intrinsically fast. However, as the accuracy requirements increase, the number of comparators increases as 2N where N is the number of bits. In the case of an 8 bit Flash ADC, there are 256 comparators. The 256 comparator output signals are routed to a decoder circuit that produces and 8 bit digital word. The schematic for a Flash converter is shown in Fig. 1. The focus of this paper is on a new implementation of an 8 bit Flash converter utilizing optical technologies.