Differential Measurement Circuit Calibration for Amplifier Offset Errors
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Solution Overview
Problem
Real-world differential measurement circuitry generates incorrect output voltages even when input signals change equally, due to errors introduced by the differential amplifier, which affects the accuracy of measurements in test systems.
Innovation Solution
The circuitry includes a differential amplifier with calibration values (GH and GL) to correct errors by determining the differential measurement (hs−ls) using the equation (hs−ls)=Vo*GH−ls(m)*GH+GL*GH−Ofs*GH, where Vo is the output voltage, ls(m) is the low signal, and Ofs is the offset value, allowing for accurate measurement of the difference between high and low signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a differential amplifier is used to generate output voltage based on the difference between two input signals, then the measurement range and signal amplification are improved, but measurement precision deteriorates due to errors introduced by the amplifier
Solution Approach 1:
The system performs preliminary calibration measurements by applying known test signals (first test signal with high voltage magnitude and low voltage magnitude, second test signal with different voltage magnitudes) before actual differential measurements. This preliminary action characterizes the amplifier's error behavior and stores calibration data that will be used to correct subsequent measurements, thereby resolving the precision problem before it affects actual measurements
Solution Approach 2:
The system uses feedback by comparing the amplifier's actual output against expected outputs from known test signals, characterizing the error, and then applying correction factors to subsequent measurements. The calibration process establishes a feedback loop where measurement errors are continuously compensated based on pre-characterized amplifier behavior
2Measurement precision
If calibration measurements are performed with known test signals to correct amplifier errors, then measurement precision is improved, but device complexity increases due to additional measurement circuits and calibration procedures
Solution Approach 1:
The measurement circuits are designed to perform multiple functions: they can apply test signals, measure amplifier outputs during calibration, and perform actual differential measurements. This multi-functionality reduces the need for separate dedicated calibration equipment, thereby limiting the increase in device complexity while still achieving improved precision
Solution Approach 2:
The system performs its own calibration using internal measurement circuits and processing logic, eliminating the need for external calibration equipment. The differential measurement circuitry characterizes its own amplifier errors and applies self-correction, making the system self-sufficient and avoiding additional complex external calibration devices
3Manufacturing precision
If separate calibration measurements are performed for high and low signals, then manufacturing precision is improved, but loss of time increases due to multiple calibration steps
Solution Approach 1:
The system merges multiple calibration measurements into a unified calibration process. By applying test signals and measuring outputs in an integrated manner, the system characterizes both high and low signal amplification errors simultaneously or in sequence within a single calibration routine, reducing the total time compared to completely separate calibration procedures for each signal level
Data Source
AI summary
Example circuitry includes a first circuit to provide a low signal; a second circuit to provide a high signal, where the high signal has a greater voltage magnitude than the low signal; and a differential amplifier configured to receive the low signal from the first circuit and the high signal from the second circuit. The differential amplifier is for producing an output voltage that is based on the high signal and the low signal. The example circuitry includes a first measurement circuit to measure the output voltage; a second measurement circuit to measure the low signal at the first circuit; and processing logic to determine a differential measurement based on the output voltage measured by the first measurement circuit, the low signal measured by the second measurement circuit, and calibration values obtained for the circuitry.