Light Detection Circuit for DLP Projector Color Wheel Index
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Solution Overview
Problem
DLP projectors face challenges in accurately detecting the color wheel index signal due to environmental dust and element sensitivity, which affects the noise margin and imaging quality.
Innovation Solution
A light detection circuit with a light transistor, bias unit, operation amplifier, and feedback resistor is used to accurately detect the color wheel index signal by operating the light transistor in a linear region, ensuring the output voltage is highly correlated with the reflected light, allowing precise control of the color wheel rotation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional light detection methods are used, then the detection circuit is simple, but the detection precision is low due to dust and sensitivity issues
Solution Approach 1:
The patent changes the operating parameters of the light transistor by introducing a feedback resistor to operate it in the linear region rather than saturation region. This parameter change enables the output current to be linearly proportional to the incident light intensity, significantly improving detection precision for color wheel index signals while maintaining a relatively simple circuit structure.
Solution Approach 2:
The patent introduces a feedback resistor connected between the collector and base of the light transistor to create a feedback mechanism. This feedback controls the base-emitter voltage to keep the transistor operating in the linear region, thereby improving the linearity between output current and incident light intensity, which enhances detection precision without substantially increasing circuit complexity.
2Measurement precision
If the light transistor operates in saturation region, then the circuit is simple, but the output is not linearly correlated with reflected light
Solution Approach 1:
The patent changes the operating point of the light transistor from saturation region to linear region by adjusting the base current through the feedback resistor. This parameter change ensures that the collector current is linearly proportional to the base current and thus to the incident reflected light intensity, improving measurement precision while keeping the circuit structure relatively simple.
Solution Approach 2:
The feedback resistor creates a negative feedback loop that automatically adjusts the base-emitter voltage to maintain linear operation. When incident light increases, the collector current increases, which through the feedback resistor increases the base voltage, thereby increasing base current to compensate and maintain linearity between output and incident light.
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 solution enhances the noise margin and imaging quality of DLP projectors by accurately detecting the color wheel index signal and controlling its rotation, leading to improved projection quality.
Implementation Method 1
a light transistor for receiving and sensing a reflected light from a side of a color wheel driving motor
Data Source
AI summary
A light detection circuit for a projector is provided. The light detection circuit includes: a light transistor for receiving and sensing reflected light from a side of a color wheel driving motor of the projector, wherein the side of the color wheel driving motor includes a dark region and a bright region; a bias unit coupled to the light transistor for providing a bias voltage; an operation amplifier including a positive input coupled to the bias unit, a negative input coupled to the light transistor and the bias unit, and an output, the base unit providing the bias voltage to the positive input; and a feedback resistor coupled between the negative input of the operation amplifier and the output, wherein, a resistance of the feedback resistor causes the light transistor to be operated in a linear region.