Optical Scanning Mirror Detection with Dummy Capacitance Noise Balancing
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Solution Overview
Problem
Existing optical scanning apparatuses suffer from noise interference in the detection of the deflection angle of a movable mirror, which affects the accuracy of the signal used for scanning.
Innovation Solution
The apparatus includes a mirror with a reflective surface driven by piezoelectric actuators, a detection section using capacitance changes, and a dummy capacitance section to balance parasitic capacitances, all integrated within a semiconductor layer, forming series connections to cancel out common noise components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a detection section is used to detect the deflection angle of a movable mirror, then the deflection angle can be measured, but noise is mixed into the detection signal
Solution Approach 1:
A dummy capacitance section is introduced as an intermediary element that mirrors the detection section's capacitance characteristics. This dummy section captures and isolates parasitic capacitance and noise, preventing these harmful factors from contaminating the actual deflection angle detection signal while maintaining measurement precision
Solution Approach 2:
The dummy capacitance section is designed to replicate the electrical characteristics of the detection section by forming capacitance between corresponding electrodes in the same semiconductor layer. This copying approach ensures that the dummy section experiences identical parasitic effects, allowing it to serve as an effective noise reference for signal cancellation
2Measurement precision
If capacitance-based detection is used to detect driving section movement, then movement can be measured, but parasitic capacitance occurs between electrodes and support layer
Solution Approach 1:
The parasitic capacitance between electrodes and support layer, which was previously a harmful factor degrading signal quality, is converted into a useful reference signal. The dummy capacitance section deliberately replicates this parasitic capacitance, allowing the harmful effect to be measured and subtracted from the detection signal, thereby improving measurement accuracy
Solution Approach 2:
The invention changes the electrical parameter configuration by creating a matched pair of capacitance sections with equivalent parasitic characteristics. By adjusting the dummy capacitance section to match the detection section's parasitic parameters, the system transforms the unwanted parasitic capacitance into a controllable variable that can be compensated for in the signal processing
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 reduces noise in the deflection angle detection signal, enhancing the accuracy of the scanning process without increasing costs by maintaining a balanced capacitance system.
Implementation Method 1
a detection section that detects the movement of the driving section by change of a capacitance
Implementation Method 2
a driving section that swings the mirror
Data Source
Figure 1
Figure 2A~2B
Figure 3A~3B
AI summary
To reduce noise of a signal used to detect deflection angle of a mirror. An optical scanning apparatus including a mirror, a detection section, and a dummy capacitance section is disclosed. The detection section generates capacitance between a movable and a fixed electrode. The dummy capacitance section generates dummy capacitance between a first and a second electrode. These four electrodes are provided on the same active layer and are each separated. The active layer is arranged to face a support layer with an insulating layer inbetween. A first parasitic capacitance generated between the active layer including the fixed electrode and the support layer is equivalent to a second parasitic capacitance generated between the active layer including the first electrode and the support layer. The capacitance of the detection section and the first parasitic capacitance are connected in series, the dummy capacitance and the second parasitic capacitance are connected in series.