APD Optical Power Monitoring With Offset-Corrected Current Mirror
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Solution Overview
Problem
Current optical power monitoring devices using avalanche photo diodes (APDs) face limitations in achieving high speed and precision, particularly in accurately measuring optical power and correcting for offset fluctuations.
Innovation Solution
The solution involves a photodiode connected in parallel with a resistor, a current mirror circuit, and a control unit that stores and uses pre-calibrated current values to accurately detect and correct the current flowing through the photodiode, improving response speed and precision by employing a temperature sensor and voltage control to stabilize the APD's output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a current mirror circuit is used to detect the sum of currents, then the measurement capability is improved, but the response speed is reduced due to circuit complexity
Solution Approach 1:
The current detection is segmented into two independent paths: one path detects the sum of currents through the current mirror circuit for accurate measurement, while the other path directly measures the photodiode current for fast response. This segmentation allows each path to optimize for its specific function, resolving the contradiction between measurement accuracy and response speed.
Solution Approach 2:
The resistor connected in parallel to the photodiode acts as an intermediary element. It provides a reference current path that enables the current mirror circuit to function accurately without directly impacting the photodiode's response speed. The resistor mediates between the need for accurate current measurement and the requirement for fast response.
2Measurement precision
If offset correction is implemented to improve measurement accuracy, then the precision is improved, but the device complexity increases
Solution Approach 1:
Offset correction values are pre-calculated and stored in a lookup table during the design phase. During operation, the system simply retrieves the appropriate offset value based on temperature or other parameters, rather than performing complex real-time calculations. This preliminary action reduces the computational burden and circuit complexity while maintaining high measurement accuracy.
Solution Approach 2:
The system uses temperature as a parameter to select appropriate offset correction values. By changing the parameter (temperature) and having pre-stored correction values for different parameter states, the system achieves accurate offset correction without requiring complex real-time analysis circuits.
3Measurement precision
If high precision measurement is achieved through complex correction circuits, then the measurement accuracy is improved, but the cost increases
Solution Approach 1:
The patent uses a simple resistor as a disposable, low-cost component to enable offset correction functionality. Rather than using expensive, complex correction circuits, the system employs inexpensive resistors that can be easily manufactured and replaced, achieving the same functional goal at a fraction of the cost.
Solution Approach 2:
The system uses a current mirror circuit to create a copy of the photodiode current path. This copying approach allows the system to measure current accurately using simple, low-cost components rather than requiring expensive direct measurement instruments, achieving high precision through circuit replication rather than expensive hardware.
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
This configuration enhances the accuracy and speed of optical power monitoring by correcting offset fluctuations and utilizing a low-cost resistor to improve the responsiveness of the current mirror circuit, allowing for precise measurement of received optical power.
Implementation Method 1
a photodiode which converts a received optical power to a current
Data Source
AI summary
An optical power monitoring device is provided with: an APD as a photodiode that converts the power of light to a current (Iapd); a resistor that is connected in parallel to the APD; a current mirror circuit that detects, as a first current value (I1), the value corresponding to the sum of the current (Irb) flowing through the resistor and the current (Iapd) flowing through the APD; and a control unit. The control unit stores in advance a value corresponding to the current flowing through the resistor as a second current value (I2), and determines the current (Iapd) flowing through the APD on the basis of the second current value (I2) and the first current value (I1) detected by the current mirror circuit.