Full Custom Design of a 8-bit Subranging Flash A/D Convertor

Abstract

This paper describes the design of a Nonius Flash Analog to Digital Convertor for video-applications. The conversion is split up in two stages: the MSB and the LSB conversion stage. In the LSB conversion stage, the reference-voltage for the comparators is shifted up and down as a nonius of a vernier gauge, according to the MSB conversion obtained in the first half clock cycle. The MSB's and LSB's are simultaneously available at the output to make a 8-bit representation of the analog signal. Using the subranging mechanism, the number of comparators is reduced from 256 to 32 and the Nonius approach results in a very simple configuration for the subranging switches. The design has been simulated with HSPICE in ES2 1. 5 CMOS technology.