一种改进型低输入偏置电流的仪表放大器

An improved instrumentation amplifier with low input bias current

介绍了一种低输入偏置电流仪表放大器的设计.主要采用超βNPN输入器件并配合一种改进型的偏流自补偿结构,即通过在偏流补偿网络中使用一个横向PNP型器件替换PJFET器件的方法,以防止PJFET器件高温下栅漏电流对电路造成的影响,实现pA量级的极低输入偏置电流和pA/℃量级的偏流温漂系数.基于兼容金属薄膜电阻的40V单铝双极工艺,在保证低增益误差、低失调电压和高共模抑制比的同时,该电路具有较高的输入阻抗,适用于数据采集系统中对小信号的提取和放大.测试结果显示,改进后的仪表放大器常温下的输入偏置电流为0.69nA,输入失调电流为0.12nA,输入失调电压为21.54μV,增益G=100时的增益误差为0.05%,共模抑制比为119.41dB.

This article discusses a low input bias current instrumentation amplifier,which mainly adopts ultra-βNPN 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 40 V 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 0.69 nA,the input offset current is 0.12 nA,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 119.41 dB.