Light Control Circuit Stabilizes Optical Encoder Intensity
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Solution Overview
Problem
Conventional optical detection systems face challenges in maintaining stable light intensity due to dc shifts in common mode voltage caused by dark current leakage and reflected light leakage, which affect the accurate control of light source emission.
Innovation Solution
A light control circuit is introduced that utilizes a quadrature detection technique, incorporating squaring circuits, sum circuits, and a constant voltage source to eliminate dc offsets and stabilize light emission intensity by converting current signals into voltage signals and comparing them with a reference voltage to control the light source.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional light control circuit is used, then circuit structure is simple, but dc offset cannot be eliminated causing unstable light intensity
Solution Approach 1:
The light control circuit is divided into multiple functional modules: trans-impedance amplifier for current-to-voltage conversion, common mode voltage extraction circuit for separating common mode signals, squaring circuits for signal processing, and sum circuit for combining signals. This segmentation allows each module to perform its specific function effectively, eliminating DC offset while maintaining manageable circuit complexity
Solution Approach 2:
The patent introduces intermediate processing circuits between the light detector and the final control output. The common mode voltage extraction circuit acts as an intermediary to isolate and process the common mode voltage component separately. The squaring circuits serve as intermediaries to process the detected signals before they are combined in the sum circuit, enabling DC offset elimination through systematic signal processing
2Measurement precision
If quadrature detection technique with squaring circuits is adopted, then dc offset elimination is achieved, but circuit area increases
Solution Approach 1:
The patent combines multiple signal processing functions into integrated circuit blocks. The common mode voltage extraction circuit integrates the common mode voltage detector and extraction functions. The squaring circuits are implemented as integrated functional blocks that perform both squaring and signal processing. The sum circuit combines multiple input signals in a single integrated structure, reducing the overall circuit area compared to discrete implementations
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 solution effectively stabilizes light emission intensity by eliminating dc offsets and adapting to environmental changes, ensuring accurate control of the light source's drive current and maintaining consistent light output.
Implementation Method 1
The light detector 91 is used to detect modulated light to generate a detected signal
Implementation Method 2
The trans-impedance amplifier is configured to amplify and convert the first current signal, the second current signal, the third current signal and the fourth current to respectively generate a first detected signal, a second detected signal, a third detected signal and a fourth detected signal
Data Source
AI summary
There is provided a light control circuit including a detected voltage generating circuit, a reference voltage generating circuit, an error amplifier, an NMOS driver and a light source. The detected voltage generating circuit outputs a detected voltage to a first input terminal of the error amplifier. The reference voltage generating circuit outputs a reference voltage to a second input terminal of the error amplifier. The NMOS driver changes a drive current of the light source according to an output of the error amplifier.