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

Several devices such as load cells and pressure sensors, among others, provide differential outputs. Given that present high-resolution analog-to-digital converters (ADCs) have differential inputs, fully differential (F-D) circuits are required to adapt the sensor output to the ADC input. This paper proposes an F-D conditioning circuit that 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 ±25 mV with a common-mode voltage of 5 V to a differential output signal of ±5 and 2.5 V, respectively. It shows an input-referenced peak-to-peak noise of 120 nV, which results in a 112-dB dynamic range (18.7-bit noise-free resolution) for a signal bandwidth of 10 Hz.