A Dual-Mode Conditioning Circuit for Differential Analog-to-Digital Converters

Abstract

Several devices such as load cells and pressure sensors, among others, provide differential outputs. Given that present high resolution analog-to-digital converters (ADC) have differential inputs, fully-differential (F-D) circuits are required to adapt the sensor output to the ADC input. This work proposes a fully-differential conditioning circuit which allows adjusting both differential and common mode signals to the levels required by the ADC. A design example is presented and a prototype was built and tested. It transforms a differential input signal of ±25mV with a common mode voltage of 5V to a differential output signal of ±5V and 2.5V respectively. It shows an input-referenced peak-to-peak noise of 120nV, which results in a 112 dB dynamic range (18.7 bits noise-free resolution) for a signal bandwidth of 10 Hz.