Servo Loop Input Bias Current Measurement
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Solution Overview
Problem
Conventional methods for measuring input bias current in operational amplifiers face challenges due to stray capacitance and leakage from long lead wires, requiring reference parts and inconsistent results, which complicates high-sensitivity detection in production environments.
Innovation Solution
A system and method that incorporates a servo loop with a high-sensitivity onboard instrumentation amplifier, allowing for calibration without external reference parts and minimizing stray capacitance by using a switchable parallel configuration, enabling accurate measurement of input bias current within the sub-picoampere range without the need for extended lead wires.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If long lead wires are used to connect the device under test to the remote instrumentation amplifier, then the measurement range and flexibility are improved, but stray capacitance and leakage effects increase, degrading measurement precision
Solution Approach 1:
The invention extracts the instrumentation amplifier from its conventional remote location and integrates it directly onto the same printed circuit board as the device under test. This eliminates the need for long lead wires and their associated stray capacitance and leakage effects, thereby resolving the contradiction between measurement flexibility and measurement precision.
Solution Approach 2:
The invention merges the instrumentation amplifier and the device under test into a single integrated test platform on the same PCB. This co-location eliminates the connection leads between them, removing the source of measurement errors while maintaining the ability to perform accurate input bias current measurements.
2Measurement precision
If a remote integrator with servo loop is used to achieve high sensitivity measurement, then measurement precision is improved, but the system requires reference parts and periodic calibration, increasing device complexity and reducing productivity
Solution Approach 1:
The invention implements self-calibration by using the integrated instrumentation amplifier to automatically characterize and compensate for its own input bias current. The system performs self-characterization during normal operation without requiring external reference parts or manual calibration procedures, thereby maintaining high measurement precision while reducing system complexity and improving productivity.
Solution Approach 2:
The invention performs preliminary characterization of the instrumentation amplifier's input bias current automatically during system initialization or normal operation. This pre-characterization data is stored and used for real-time compensation, eliminating the need for periodic calibration with reference parts and simplifying the test platform.
3Measurement precision
If conventional pico-amp meter techniques are used with remote instrumentation amplifiers, then input bias current can be converted to voltage for measurement, but lead wire effects create measurement floor and drift, reducing reliability
Solution Approach 1:
The invention removes the problematic lead wires from the signal path by integrating the instrumentation amplifier directly with the device under test on the same PCB. This extraction eliminates stray capacitance and leakage effects that cause measurement floor and drift, thereby maintaining the current-to-voltage conversion capability while significantly improving measurement reliability and consistency.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
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.
Implementation Method 1
a servo loop which integrates the input bias current over time via a sensing capacitor
Implementation Method 2
the remote amp can serve to convert the input bias current to voltage, and measure the value of the input bias current over time based on the converted voltage
Data Source
AI summary
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.