This paper presents a direct digital converter for Wheatstone bridge sensors, which is realized with commercial off-the-shelf components. The power efficiency of the readout is enhanced by embedding the bridge sensor in a second-order continuous-time sigma-delta modulator (CTDeltaSigmaM). By directly digitizing the output signal of a Wheatstone bridge in the current mode, the noise performance is dominated by the operational amplifier in the first integrator and the bridge sensor. To demonstrate the performance of the proposed circuit, an MEMS piezoresistive differential pressure sensor is used. Measurement results show that a resolution of 12.7 mParms (0.41 mOhmrms), with a 0.5-ms conversion time, can be achieved. Powered by 5 V, the circuit and the bridge sensor draw 9.55 and 7.58 mW, respectively.
- Direct digital converter
- bridge sensor readout
- continuous-time sigma-delta modulator
- mPa-level differential pressure sensing