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This paper constructs and simulates the interface circuit of a temperature sensor based on SMIC 0.18 $\mu$m CMOS. The simulation results show that when the power supply voltage is 1.8 V, the chopper op-amp gain is 89.44 dB, the low-frequency noise is 71.83 nV/Hz,${}^{1/2}$ and the temperature coefficient of the core temperature sensitive circuit is 1.7808 mV/${}^{\circ }$C. The sampling rate of 10-bit SAR ADC was 10 kS/s, effective bit was 9.0119, SNR was 59.3256 dB, SFDR was 68.7091 dB, and THD was −62.5859 dB. The measurement range of temperature sensor interface circuit is −50${}^{\circ }$C$\sim +125^{\circ }$C, the relative temperature measurement error is ±0.47${}^{\circ }$C, the resolution is 0.2${}^{\circ }$C/LSB, and the overall average power consumption is 434.9 $\mu$W.

This paper presents a high-efficiency operational amplifier (op-amp) used in the readout circuit of micro-sensor. The chopping and dynamic element matching (DEM) techniques are used in the proposed design, which greatly reduce the offset voltage and flicker noise $(1/f$ noise) of the op-amp. By optimizing the circuit structure, the maximum chopping frequency is increased to 2MHz when the offset voltage is less than $20\mu$V. Therefore, the maximum bandwidth of signal processing can be up to 1MHz. The proposed circuit is designed and fabricated using TSMC 0.18-$\mu$m 1P5M CMOS technology. It occupies an area of 0.16mm² and consumes $75\mu$A from a 1.8-V supply. When the chopping frequency is 100kHz, the input-referred offset voltage is 4.21$\mu$V and the input-referred noise is 42nV$/\surd$Hz. It achieves a noise efficiency factor of 7.82 and a power efficiency factor of 110.07.