A 21-bit read-out IC employing dynamic element matching with 0.037% gain error

A 21-bit read-out IC (ROIC) with ±40mV full scale for interfacing bridge transducers and thermocouples has been realized in a 0.7μm CMOS process. The ROIC consists of a current-feedback instrumentation amplifier (CFIA) and a switched-capacitor (SC) ΣΔ ADC. To improve its gain accuracy, dynamic element matching (DEM) was applied to the input and feedback transconductors of the CFIA. However, the common-mode (CM) dependency of these transconductors limits the achievable gain accuracy. To enhance their CM immunity, threshold-boosting and impedance-balancing techniques have been applied. These techniques enable the ROIC to achieve a typical CMRR of 140dB and a worst-case gain error of 0.037%. Compared to recent work 10dB higher CMRR and 3.2× less gain error has been achieved for the same power consumption.