CA3420 Picoammeter: 4 Ranges Circuit Design Guide

Circuit diagram

A sophisticated circuit employing a CA3420 BiMOS operational amplifier is presented here, designed to function as a picoammeter featuring four distinct measurement ranges. The amplifier’s remarkably low input current – typically 0.2pA – renders it exceptionally well-suited for implementation in picoammeter circuits. Input surge protection is implemented through a 1 megohm resistor incorporated in series with the input. A 10 megohm resistor connected to pin 2 serves to decouple the considerable input capacitance frequently encountered in circuits operating at low current levels, thereby mitigating the likelihood of circuit oscillation under these conditions. The 10k potentiometer is utilized for offset calibration.

CA3420 BiMOS Operational Amplifier

The CA3420 is a versatile BiMOS operational amplifier that is known for its low input bias current, making it ideal for precision current measurement applications. It offers a high open-loop gain and excellent common-mode rejection ratio. This amplifier is frequently used in instrumentation and measurement devices. Its ability to handle very small currents with minimal distortion contributes to the accuracy of the picoammeter.