Light Receiving Circuit With Threshold Compensation for Low PWD
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Solution Overview
Problem
Conventional light receiving circuits experience pulse width distortion (PWD) in their output signals due to changes in light input power, affecting the switchover time of the electric current comparator.
Innovation Solution
The light receiving circuit incorporates a photodiode, transimpedance amplifier, electric current comparator, automatic threshold control circuit, and current mirror circuit, with specific MOS transistors and constant electric current sources to maintain a consistent threshold value, reducing PWD by ensuring the switchover time remains constant regardless of light signal strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the light input power is changed, then the output signal level changes, but the switchover time of the electric current comparator changes causing pulse width distortion
Solution Approach 1:
The patent changes the threshold parameter of the electric current comparator dynamically by adding a light input power compensation current. This compensation current is generated based on the detected light input power level and is added to the threshold current, thereby adjusting the comparator's switching point to compensate for PWD effects and maintain consistent pulse width across different signal levels
Solution Approach 2:
The patent implements a feedback mechanism where the light input power detection circuit continuously monitors the input power level and feeds this information back to the threshold control circuit. This feedback loop enables real-time adjustment of the comparator threshold to maintain accurate switchover timing despite variations in input power
2Device complexity
If a conventional electric current comparator is used, then the circuit structure is simple, but the switchover time varies with light input power causing distortion
Solution Approach 1:
The patent introduces a light input power compensation current as an intermediary element that mediates between the variable light input power and the comparator threshold. This compensation current acts as a corrective factor that adjusts the threshold dynamically without requiring complete redesign of the comparator circuit, thus maintaining structural simplicity while improving reliability
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 effectively decreases signal distortion by maintaining consistent switchover times for both increasing and decreasing light signals, achieving low pulse width distortion characteristics.
Implementation Method 1
a photodiode for photoelectric conversion of light signal into an electric signal
Data Source
AI summary
A light receiving circuit includes a photodiode, a transimpedance amp having a feedback resistor, an electric current comparator and an automatic threshold control circuit that includes a current mirror circuit for forming a current according to the mirror effect. With this light receiving circuit, regardless of how powerful the input light signal is, low pulse width distortion characteristics can be achieved.