MEMS Scanning Projector Pixel Clocking for EMI-Resistant Beam Positioning
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Solution Overview
Problem
Existing scanned beam display devices are susceptible to electromagnetic interference (EMI) due to the use of sensitive analog circuits for generating pixel clocks, which can affect the accuracy and stability of image scanning and display.
Innovation Solution
A projection system utilizing a free-running oscillator and digital phase lock loop (PLL) circuit to generate an asynchronous pixel clock, combined with a microelectromechanical system (MEMS) device and image processing components that interpolate pixel data, allowing for non-linear scan trajectories and reducing the impact of EMI by using a spread spectrum clock.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an analog voltage controlled oscillator is used to generate the pixel clock, then the pixel clock can be phase locked to the sync signal for accurate beam positioning, but the system becomes susceptible to electromagnetic interference (EMI)
Solution Approach 1:
The patent replaces the analog voltage controlled oscillator with a digital free-running oscillator and digital phase lock loop circuit. This substitution of digital electronics for analog circuits eliminates the susceptibility to electromagnetic interference while maintaining the ability to generate an accurate pixel clock synchronized to the sync signal for precise beam positioning.
Solution Approach 2:
The patent changes the operating parameters by using a free-running oscillator with a frequency close to the desired pixel clock frequency, then correcting phase errors through digital processing. This approach allows the system to operate with a stable digital oscillator that is less susceptible to EMI while achieving accurate synchronization through digital phase correction rather than analog phase locking.
2Device complexity
If a linear pixel clock is used for scanning, then the circuit is simple, but the system cannot accommodate non-linear scan trajectories such as sinusoidal patterns
Solution Approach 1:
The patent implements dynamic scan trajectories by allowing the beam to follow non-linear paths such as sinusoidal patterns in both horizontal and vertical directions. The system uses phase error correction to accommodate these dynamic trajectories while maintaining synchronization, enabling the display to adapt to different scan patterns without requiring completely different circuit architectures.
Solution Approach 2:
The patent creates a universal scanning system that can handle multiple scan trajectory types (linear, sinusoidal, and other non-linear patterns) using a single digital phase lock loop architecture. This multi-functional approach allows the same circuit to support various display modes and scan patterns, increasing versatility without proportionally increasing complexity.
3Reliability
If phase locking is used to synchronize the pixel clock to the sync signal, then accurate timing is achieved, but analog circuits are more vulnerable to EMI
Solution Approach 1:
The patent replaces the analog phase locking mechanism with a digital phase lock loop. The digital circuit measures phase errors between the free-running oscillator and the sync signal, then corrects timing deviations through digital processing. This substitution maintains accurate timing synchronization while eliminating the EMI susceptibility inherent in analog phase locking circuits.
Solution Approach 2:
The patent introduces a digital intermediary processing stage between the oscillator and the pixel clock generation. The digital phase lock loop acts as an intermediary that measures and corrects phase errors without requiring direct analog coupling, thereby isolating the timing-critical circuits from electromagnetic interference while maintaining synchronization accuracy.
Data Source
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AI summary
A scanning projector (100) includes a mirror (142) that scans in two dimensions, at least one of which is sinusoidal. A digital phase lock loop (170) locks to the sinusoidal movement of the mirror. A free-running pixel clock is provided. An interpolation component interpolates pixel intensity data from adjacent pixels based on the position of the mirror when a pixel clock arrives.