Systems and methods for high-sensitivity detection of input bias current

Abstract

The invention relates to systems and methods for high-sensitivity detection of input bias current. The invention more particularly relates to platforms and techniques for the calibration and measurement of input bias current in op amps or other devices. In embodiments, the platform can incorporate a servo loop connected to a high-sensitivity test amplifier, such as an instrumentation amplifier. The test amplifier can complete a switchable circuit with the servo loop and detect a calibration input bias current for the test platform, without a production device in place. The device under test can be switched into the servo loop, and the total bias current measured with both the device under test and test amplifier in-circuit. The difference between the measured current with the device inserted and the previously measured calibration current represents the bias current for the subject device, without attaching external meters or requiring reference parts of the production type.

Description

FIELD[0001]The present teachings relate to systems and methods for high-sensitivity detection of input bias current, and more particularly, to platforms and techniques for testing the low-level input bias current of production operational amplifiers.BACKGROUND OF RELATED ART[0002]Operational amplifiers (often abbreviated “op amps”) are common semiconductor parts often configured to provide amplification of a comparative or differential signal represented by the difference between inputs on a positive (“+”) pin and a negative (“−”) pin. Op amps are often used to amplify low-level signals. In order to achieve better amplification results, particularly at the limits of amplifier sensitivity, it is useful for the manufacturer of op amp parts to be able to identify the inherent leakage current, or input bias current, that flows into the op amp inputs in the absence of an input signal.[0003]It is known to attempt to measure the input bias current (sometimes referred to as IIB current) of ...

AI Technical Summary

Benefits of technology

This approach provides high-accuracy input bias current measurements for production lots without the need for reference parts or long lead wires, enhancing measurement precision and consistency by calibrating the system internally and subtracting the instrumentation amplifier's contribution from the total measured current.

Problems solved by technology

In conventional configurations of this type, although the remote instrumentation amp may have higher sensitivity than the op amp under test, the attachment of lead wires, which can be up to several inches in length or more, can produce stray capacitance, leakages, or other electrical effects which offset or distort the high-sensitivity measurement by the remote PAM.

These unintended effects can skew or invalidate the input bias current results.

While some of these effects can be measured and calibrated out, those leakages and other effects may not be stationary over time, creating a measurement floor due to that drift.

The resulting voltage ramp is not, however, guaranteed to produce consistent results depending on the characteristics of each op amp or other device under test.

This requires the periodic insertion and verification of the remote integrator platform using such reference or correlation parts, which may not be efficient or desirable in a manufacturing or other production environment.

Images