A High-Gain, Low-Voltage Operational Amplifier With Bias-Stress and PVT Robustness for Large-Area Temperature Sensing on LTPS Substrates

Abstract

This paper analyzes the temperature coefficients of low temperature polysilicon (LTPS) devices and investigates critical blocks of a system architecture for large-area temperature sensing, which integrates sensors and readout circuits monolithically. As part of this system, a low-voltage folded-cascode (LV-FC) operational amplifier (OpAmp) with a class-AB output stage was designed and implemented using an LTPS thin film transistor (TFT) process on a 15 μ m-thick polyimide flexible substrate. The performance of 20 amplifier samples was thoroughly characterized under DC, AC, long-term bias-stress (up to 40,000 seconds), and temperature conditions (0 °C to 80 °C). The amplifier achieves a maximum DC gain of 64.2 dB and a gain-bandwidth product of 400 kHz, while operating reliably under a 6 V supply with a peak power consumption of 0.6 mW in a compact area of 1.38 mm2. Under bias stress, the gain degraded by only 2.5 dB and the offset shifted by 1.5 mV. Over the full temperature range, the average gain varied by less than 2 dB and the offset by under 6 mV. These results demonstrate strong robustness against PVT variations and prolonged stress, confirming the suitability of the proposed LV-FC amplifier for flexible, long-term, and large-area temperature sensing applications.