An improved instrumentation amplifier with lowinput bias current

This article discusses a low input bias current instrumentation amplifier, which mainly adopts ultra-β NPN input devices and cooperates with an improved bias current self-compensation structure, That is, by replacing the PJFET device with a lateral PNP device in the bias current compensation network, to prevent the gate leakage current of the PJFET device from affecting the circuit at high temperatures, and to realizes an extremely low input bias current of the order of pA and a bias current temperature drift coefficient of the order of pA/℃. Based on a 40V single aluminum bipolar process compatible with metal film resistors, this circuit has a high input impedancewhile ensuring low gain error, low offset voltage and high common mode rejection ratio, which is suitable for Small signal extraction and amplification in data collection systems.The test results show that the input bias current of the improved instrumentation amplifier at room temperature is 0.69nA, the input offset current is 0.12nA, and the input offset voltage is 21.54μV. When the gain G=100, the gain error is 0.05%, and the common mode rejection ratio is 119.41dB.