A Precision Low-Noise Sensor Readout System With BJT-Input-Based Amplifier and High-Input-Impedance Delta–Sigma ADC

This letter presents a precision low-noise sensor readout system with a bipolar junction transistor (BJT)-input-based amplifier and a high-input-impedance delta–sigma analog-to-digital convertor (ADC). The proposed sensor readout system can precisely drive the resistive sensors and attain high accuracy by adopting the low-noise BJT-input-based amplifier implementing gated p-n-p and the high-input-impedance delta–sigma ADC. The high-input-impedance delta–sigma ADC is implemented with a fully differential ping-pong autozeroing multipath differential difference amplifier (DDA), which can achieve high input impedance and low power consumption due to the DDA scheme that does not require input buffers. The proposed sensor readout system is fabricated in the standard 0.18-μm complementary metal–oxide–semiconductor process with a total active area of 3.75 mm². The total current consumption of the sensor readout system is 543.9 μA with 1.8-V power supply. The proposed sensor readout system has an ultralow-noise performance of the measured input offset and input referred noise of 1.7 μV and 5.3 nV/√Hz, respectively. The measured signal-to-noise-and-distortion ratio in a 1-kHz bandwidth is 76.4 dB.