Photodetector Nonlinearity Measurement Using Self-Referential Calibration
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Solution Overview
Problem
Existing methods for determining the nonlinearity of photodetectors, especially in wearable biomonitoring devices, suffer from systematic measurement errors due to the need for external calibration of illumination sources and are inaccurate, often providing results with errors exceeding 100 ppm.
Innovation Solution
A self-referential measurement method using phase-sensitive rectifiers to measure the output signals of photodetectors illuminated with both time-variable and temporally constant electromagnetic radiation, allowing direct proportionality between the measurement signal and radiation intensity without external calibration, and determining nonlinearity by comparing output signals at different intensities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If external calibration of illumination sources is used to measure photodetector nonlinearity, then measurement can be performed, but systematic measurement errors exceed 100 ppm
Solution Approach 1:
The measurement method uses the photodetector itself to generate the calibration signal through self-heating effects, eliminating the need for external calibrated illumination sources. The photodetector's own response to controlled heating provides the reference signal, making the system self-calibrating and eliminating external calibration errors.
Solution Approach 2:
Temperature serves as an intermediary parameter that couples the electrical measurement system with the optical response. By controlling and measuring temperature changes in the photodetector, the method creates a controlled intermediate state that reveals nonlinearity without requiring external optical calibration.
2Device complexity
If conventional measurement methods are used, then simplicity is maintained, but measurement errors exceed 100 ppm
Solution Approach 1:
The method changes the operating parameters of the photodetector by applying controlled temperature variations and bias voltage changes. These parameter changes induce measurable effects (current changes, resistance changes) that reveal nonlinearity characteristics without requiring complex external calibration equipment.
3Measurement precision
If high accuracy nonlinearity measurement is achieved with less than 100 ppm error, then measurement precision is improved, but measurement system complexity increases
Solution Approach 1:
The method replaces complex optical calibration mechanisms with electrical measurement and controlled thermal effects. Instead of using mechanical or optical calibration sources, the system uses electrical biasing and thermal coupling that can be precisely controlled and measured with standard electrical instrumentation.
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 method achieves a high accuracy in determining photodetector nonlinearity with less than 100 ppm error, reducing systematic errors and improving measurement precision.
Implementation Method 1
illumination of a photodetector to be characterized with a variable electromagnetic radiation... The variable electromagnetic radiation is, for example, light... and is generated by means of an illumination element
Implementation Method 2
The variable electromagnetic radiation is generated by means of an optoelectronic semiconductor element, for example a light-emitting diode or a laser diode. In the example of the light-emitting diode, the variable electromagnetic radiation is generated by applying an electric voltage to the light-emitting diode
Implementation Method 3
the output signal of the photodetector is measured by means of a phase-sensitive rectifier, also referred to as a lock-in amplifier. A reference signal with the same period and phase as that of the variable, temporally oscillating electromagnetic radiation is applied to the corresponding input of the phase-sensitive rectifier
Data Source
AI summary
A measurement method for characterization of a photodetector includes illumination of the photodetector with a variable electromagnetic radiation. The variable electromagnetic radiation has a temporally oscillating radiation intensity with fixed period and amplitude. The method also includes illumination of the photodetector with a first electromagnetic radiation having a temporally constant first radiation intensity and measurement of a first output signal at the photodetector. The method further includes illumination of the photodetector with a second electromagnetic radiation having a temporally constant second radiation intensity different from the first radiation intensity and measurement of a second output signal at the photodetector. The method additionally includes determination of a non-linearity of the photodetector by comparing the measurements of the first and second output signals.