Photodetector Control Circuit Temperature Compensation
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Solution Overview
Problem
Conventional Hall element-based systems for detecting lens position in cameras are costly and unsuitable for space-constrained devices like smartphones, necessitating an alternative method for accurate and temperature-compensated position detection.
Innovation Solution
A photodetector control circuit utilizing a phototransistor to detect reflected light from a photodiode, which includes units for detecting and controlling current, estimating temperature effects, and modifying diode current to achieve effective temperature compensation, enabling precise lens position detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a Hall element is used for detecting lens position, then detection accuracy is improved, but device cost increases and space requirements are not satisfied
Solution Approach 1:
The patent replaces the Hall element-based magnetic detection system with an optical detection system using a photodiode and phototransistor. This substitution eliminates the need for magnetic components and complex circuitry, reducing both cost and space while maintaining detection functionality through optical reflection principles
Solution Approach 2:
The patent uses optical reflection to create a virtual image of the lens position on a photodetector surface. By detecting the position of this optical image rather than directly measuring magnetic fields, the system achieves accurate position detection with simpler, cheaper components that occupy less space
2Ease of manufacture
If a photodetector is used for lens position detection, then device cost and space are reduced, but temperature sensitivity increases requiring compensation
Solution Approach 1:
The patent implements temperature compensation by detecting the forward voltage drop of the photodiode, which varies with temperature. This temperature information is fed back to adjust the reference voltage in the detection circuit, compensating for temperature-induced drift and maintaining detection accuracy across varying thermal conditions
Solution Approach 2:
The patent changes the electrical parameters (voltage and current) of the photodiode and phototransistor based on detected temperature conditions. By dynamically adjusting these parameters, the system compensates for temperature effects on optical properties and electrical characteristics, maintaining stable operation across temperature ranges
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 provides accurate and temperature-compensated lens position detection, addressing the cost and space limitations of Hall element systems while ensuring reliable operation across varying temperatures.
Implementation Method 1
light emitted from a photodiode
Implementation Method 2
a photodetector such as a photo-reflector or a photo-interrupter may be used. A photo-reflector is a device in which light emitted from a photodiode is reflected off a target and the reflected light is detected using a phototransistor
Implementation Method 3
a voltage detecting unit for detecting a temperature based on a forward drop voltage of the photodiode
Data Source
AI summary
A photodetector control circuit in a photodetector for detecting light from a photodiode using a phototransistor and controls drive of the photodiode and detection of a current of the phototransistor has a received light amount detecting unit that detects a detection current, which flows through the phototransistor in accordance with a received light amount, by converting the detection current into a detection voltage, and compares the detection voltage with a reference voltage detected during reception of a reference light amount, to thereby detect a change in the received light amount, a diode current control unit for controlling a diode current that is caused to flow through the photodiode, and a control unit that detects a temperature based on a forward drop voltage of the photodiode and estimates a current change rate of the phototransistor based on the detected temperature.