Photodiode Amplifier Offset Compensation for High-Temperature Sensing
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Solution Overview
Problem
Photodiodes in gas turbine engines experience errors due to high temperatures, leading to inaccurate temperature measurements caused by increased dark current and shunt resistance, which existing technologies fail to adequately compensate for.
Innovation Solution
A system comprising a live photodiode exposed to a light source and a reference photodiode isolated from the light source, with a controller generating a compensated output signal by subtracting the reference signal from the live signal, using a photodiode switch and sample and hold circuits to alternate between live and reference signals, and a difference amplifier to correct for errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If photodiodes are exposed to high temperatures in gas turbine engines, then temperature measurement capability is maintained, but dark current increases causing measurement errors
Solution Approach 1:
The system divides the measurement function into two separate photodiodes: a live photodiode exposed to the light source for temperature measurement, and a reference photodiode isolated from the light source for error signal detection. This segmentation allows independent measurement of the target signal and error signals, enabling compensation of dark current effects at high temperatures.
Solution Approach 2:
The reference photodiode acts as an intermediary that measures only the error signals (dark current, shunt resistance effects) without being exposed to the light source. By subtracting the reference signal from the live signal, the system eliminates error components while preserving the temperature measurement capability.
2Measurement precision
If a reference photodiode is added to compensate for errors, then measurement accuracy improves, but device complexity increases
Solution Approach 1:
The system combines the live photodiode and reference photodiode into a single integrated sensor assembly with shared mounting structure and electrical connection through a multiplexer. This merging approach reduces overall system complexity compared to using separate independent measurement systems, while maintaining the accuracy benefits of dual photodiodes.
Solution Approach 2:
The controller performs multiple functions: it operates the photodiode switch to alternate between live and reference photodiodes, amplifies both signals through the transconductance amplifier, and executes the subtraction algorithm to generate the compensated output. This multi-functionality reduces the need for separate dedicated circuits for each operation.
3Measurement precision
If photodiode switch and sample and hold circuits are used to alternate between live and reference signals, then error compensation accuracy improves, but circuit complexity increases
Solution Approach 1:
The photodiode switch alternates periodically between connecting the live photodiode and the reference photodiode to the transconductance amplifier. This periodic switching allows the system to sample both signals in sequence, and the sample and hold circuits capture each signal at the appropriate moment. The periodic action ensures synchronized sampling that maintains accuracy while using a single amplifier for both signals.
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
The system effectively compensates for errors in photodiode signals, providing accurate temperature measurements by isolating and subtracting error signals from the reference photodiode, resulting in a compensated output that represents the temperature of the light source without significant error.
Implementation Method 1
a live photodiode configured to be exposed to a light source and to output a live signal
Implementation Method 2
a difference amplifier configured to generate a compensated output signal by subtracting the reference signal from the live signal
Data Source
AI summary
A system for compensating for photodiode errors includes a live photodiode configured to be exposed to a light source and to output a live signal. The system further includes a reference photodiode located proximate to the live photodiode and configured to be isolated from the light source and to output a reference signal. The system further includes a controller configured to generate a compensated output signal by subtracting the reference signal from the live signal.