A High Precision Operational Amplifier with Improved Bias Current Cancellation Circuit

This brief presents a four-channel amplifier featured by low-offset voltage and low input bias current, which is mainly used in high precision instruments. The amplifier consists of four modules: biasing, input amplifier, bias current cancellation circuit and output stage. The biasing network adopts cross-coupled structure to improve the precision of mirror current and the offset voltage and drift are greatly reduced by using the trimming resistor. Besides, the input bias current is greatly reduced by using the improved bias current cancellation circuit (IBCCC). This device is fabricated using a standard bipolar IC process. The test results show that the input bias current is less than 1.0nA, the typical values of offset voltage and drift is 3.4μV and 0.027μV/°C respectively.