An oversampling converter that directly digitizes low-level strain gauge transducer outputs is presented. An instrumentation amplifier and two independent chopper-stabilized delta-sigma modulators amplify and convert the transducer's output and excitation. Digital division of the two independent conversions produces a 20-b ratiometric measurement. Drift due to external thermocouple junctions and RF rectification is eliminated by AC excitation of the transducer. Interference (50/60 Hz) is eliminated by a digital FIR filter that has a -3 dB bandwidth of 15 Hz. Offset and gain errors are corrected by digital calibration. The input-referred noise of this converter is 150 nV/sub rms/ and the linearity is 110 dB. The converter gain and offset drifts are less than 2.5 p.p.m./ degrees C and 15 nV/ degrees C, respectively. This 2- mu m CMOS chip consumes 30 mW of power and has an area of 25.5 mm/sup 2/.
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