A Chopper Interface Circuit for Thermopile-Based Thermal Sensors

This paper presents a readout circuit for thermopile-based thermal sensors, suitable for contactless temperature measurements. The circuit, designed and extensively simulated in a standard 130-nm CMOS process, employs chopper stabilization in order to minimize offset and noise contributions at low frequency, while providing proper amplification to the input signal, which behaves substantially as a DC. The circuit nominal supply voltage is 1.2 V and its power consumption is approximately 260 μW. The proposed single-ended architecture solves the drawbacks of the most straightforward fully differential approach, while achieving a simulated input-referred residual offset mean value equal to 84.4 nV, with 487 nV of standard deviation. An accuracy of ±0.3°C is provided at room temperature, making the circuit suitable for medical devices, such as contactless fever thermometers, and security systems, such as motion and human presence detection sensors.