Linear Isolation Amplifier Self-Calibration for Stable Transfer Gain
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Solution Overview
Problem
Linear optoisolation amplifiers exhibit significant variation in transfer gain due to manufacturing process variations, making it challenging to achieve a consistent gain value of 1.0, and existing solutions do not provide a method to correct for variations that occur over time or across different lots of optocouplers.
Innovation Solution
An amplifier circuit with a calibration circuit and optocoupler components that automatically calibrate the transfer gain to a fixed value of 1.0 by generating a calibration signal, using a reference voltage to adjust the servo amplifier, and employing a microcontroller to control the calibration process, allowing for self-correction during system startup or upon demand.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If optocoupler-based linear isolation amplifiers are used to achieve galvanic isolation, then electrical isolation and signal transmission are enabled, but substantial variation in transfer gain (K3) occurs due to manufacturing process variations
Solution Approach 1:
The patent applies preliminary action by performing calibration of the transfer gain during the manufacturing process before the product is shipped to the customer. The calibration circuit measures the actual transfer gain (K3) of each optocoupler-based isolation amplifier and stores the measured value in non-volatile memory. This allows the system to compensate for manufacturing variations in advance, ensuring consistent transfer gain performance without requiring manual adjustment at the customer site.
2Reliability
If resistor values (R1 and R2) are altered to accommodate K3 variation, then transfer gain can be adjusted, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent applies parameter changes by measuring the actual transfer gain (K3) of each device and storing this measured parameter in non-volatile memory. Instead of physically altering resistor values, the system digitally stores and uses the measured K3 value to compensate for variations. This approach maintains fixed resistor values while achieving accurate transfer gain through parameter storage and digital compensation, reducing device complexity compared to physical resistor adjustment mechanisms.
3Reliability
If manual calibration is performed at customer site, then transfer gain can be corrected, but ease of operation and calibration time are reduced
Solution Approach 1:
The patent applies self-service by enabling the isolation amplifier to automatically calibrate itself during the manufacturing process without requiring customer intervention. The calibration circuit is integrated into the device and can autonomously measure the transfer gain, store the measured value in non-volatile memory, and use this information for compensation. This self-calibrating capability eliminates the need for manual calibration operations at the customer site, significantly improving ease of operation while maintaining reliable transfer gain correction.
4Reliability
If calibration circuitry is added to correct K3 variation, then transfer gain accuracy is improved, but device complexity increases
Solution Approach 1:
The calibration circuitry is designed to be activated during the manufacturing process for preliminary calibration, after which the measured transfer gain value is stored in non-volatile memory. The calibration circuit includes minimal components that can be easily integrated into the existing optocoupler-based isolation amplifier design. By performing calibration once during manufacturing and storing the result, the circuit complexity is minimized while still achieving reliable transfer gain stability throughout the product lifecycle.
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
Enables automatic calibration of the transfer gain to a consistent value of 1.0, accommodating variations in optocoupler properties and ensuring reliable operation across different lots and over time, thereby maintaining design accuracy and performance.
Implementation Method 1
a low voltage is set on a cathode of a calibration light emitting diode (LED), disposed on a low voltage side of the linear isolation amplifier, wherein the calibration LED generates a light signal
Implementation Method 2
receiving the light signal at a photodetector, disposed on a high voltage side of the linear isolation amplifier, wherein a switch signal is generated by the photodetector
Data Source
AI summary
An amplifier circuit may include an isolated amplifier circuit, disposed on a high voltage side of the amplifier circuit, and arranged to generate an isolated output signal. The amplifier circuit may include a first optocoupler circuit, disposed to receive the isolated output signal from the isolated amplifier circuit and an output amplifier circuit, disposed on a low voltage side of the amplifier circuit, and coupled to receive an optical output signal from the optocoupler circuit. The amplifier circuit may also include a calibration circuit, coupled to the output amplifier circuit, to generate a calibration initiation signal, and a second optocoupler circuit, disposed to receive the calibration initiation signal, and to output a switch signal, wherein a reference voltage is output to the isolated amplifier circuit.