Novel Threshold-Based Standard-Cell Flash ADC

Abstract

This paper introduces a novel standard-cell flash architecture for implementing analog-to-digital converters (ADC). The proposed ADC consists of several CMOS inverters all having their inputs connected to a common input node. The out-put of the ADC is a thermometer code generated by the inverter outputs. Depending on the relationship between the input signal and a given inverter’s threshold voltage, the output will either be ‘0’ or ‘1’. By having many inverters with different threshold voltages, it is possible to create a 3-bit flash ADC. Even though the system is inherently non-linear, mathematical optimization has been done in order to improve its linearity. The proposed circuit dissipates 6.7 mW and uses in total 672 transistors of PMOS and NMOS types. This ADC is designed and simulated using TSMC’s 0.18 μm CMOS and results show that the proposed circuit works as expected even in presence of process variations.