Design of A High Input Impedance OPA with Bi-JFET Technology

A high input impedance operational amplifier (OPA) with bipolar junction field effect transistor (Bi-JFET) technology is presented. By using JFET differential pair, it achieves very low input bias offset current (pA magnitude) and low noise (3 nV/sqrt(Hz)). Moreover, bipolar gain stage and output stage provides high open-loop gain (120 dB), high output voltage slew rate (more than 10 V/μs) and broadband performance (more than 10 MHz). The proposed OPA is very suitable for detecting and amplifying all kinds of weak signals.