Instrumentation Amplifier Auto-Calibration for Offset and Gain Errors
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Solution Overview
Problem
Integrated circuit instrumentation amplifiers face challenges with offset and gain errors, which are not efficiently calibrated during manufacturing, especially when environmental conditions change, leading to increased testing complexity and costs.
Innovation Solution
An auto-calibration method for instrumentation amplifiers that allows users to calibrate gain and offset on demand using a reference voltage, with digital control circuits adjusting constant current sources and sinks to match desired voltage levels, eliminating the need for factory calibration and accommodating varying environmental conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If factory calibration is performed to reduce offset and gain errors, then measurement precision is improved, but manufacturing time and cost increase
Solution Approach 1:
The patent implements preliminary calibration action by incorporating calibration circuits and procedures during the manufacturing process that automatically compensate for offset and gain errors. The calibration data is stored in non-volatile memory, eliminating the need for time-consuming manual calibration steps while maintaining high measurement precision.
Solution Approach 2:
The instrumentation amplifier incorporates self-calibration capabilities through internal calibration circuits that automatically adjust offset and gain parameters. The device performs self-diagnosis and self-correction using stored calibration data, reducing the need for external testing equipment and manual intervention during manufacturing.
2Measurement precision
If calibration is performed at one operating point during manufacturing, then initial precision is achieved, but performance degrades when environmental conditions change
Solution Approach 1:
The patent implements dynamic calibration by storing multiple calibration data sets corresponding to different operating conditions (temperature, supply voltage) in non-volatile memory. The system automatically selects and applies the appropriate calibration data based on current environmental conditions, maintaining high measurement precision across varying operating points rather than being fixed at a single calibration point.
Solution Approach 2:
The calibration system changes operational parameters by adjusting calibration data selection based on detected environmental conditions. When temperature or supply voltage changes exceed predefined thresholds, the system transitions between different calibration data sets, effectively adapting the amplifier's performance to match the current operating parameters.
3Reliability
If separate testing equipment is used for digital microcontroller and analog functions, then testing thoroughness is improved, but device complexity and cost increase
Solution Approach 1:
The patent merges digital and analog testing functions into a unified testing architecture. The digital microcontroller directly controls analog calibration circuits and reads back calibration results through integrated interfaces, eliminating the need for separate external testing equipment. This integration maintains comprehensive testing capability while reducing overall system complexity and cost.
Solution Approach 2:
The testing system is designed with multi-functionality, where the digital microcontroller serves dual purposes: controlling the instrumentation amplifier's normal operation and managing calibration/testing operations. The same digital interfaces and logic circuits are used for both signal processing and calibration verification, reducing the need for dedicated separate testing hardware.
Data Source
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AI summary
Calibration of gain and/or offset of an instrumentation amplifier (INA) is accomplished by coupling an appropriate number of current sources, and/or current sinks, respectively, to first and/or second transconductance stage(s) of the INA. Gain and/or offset calibration of the INA may occur when requested by a user and/or the occurrence of an event(s). A voltage reference may be used in combination with a successive approximation register analog-to-digital converter in determining which ones of the current sources and sinks are coupled to the first and/or second transconductance stage(s) of the INA for gain and/or offset calibration thereof. After the gain and/or offset calibration of the INA is completed, the selection of the constant current sources and sinks used therefore may be stored in volatile or nonvolatile memory. Parity checking of the memory may be incorporated and if a parity error is detected, an auto-calibration of the INA may be initiated.