Tunable Notch Filter for MEMS Scanner Oscillation Suppression

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Solution Overview

Problem

MEMS scanning mirrors in pico-projection systems face challenges with multiple resonant modes, particularly the first mode interfering with vertical sweep, leading to distortion due to high Q values and frequency mismatches, making fixed notch filtering impractical in high volume manufacturing.

Innovation Solution

Implementing a tunable notch filter with a phase-compensated feedback loop that self-tunes to precisely match the MEMS first mode frequency, using adaptive filtering to adjust the notch filter settings and ensure accurate suppression of undesirable oscillations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If a fixed frequency notch filter is used to suppress first mode oscillations, then the distortion can be reduced, but the filter becomes impractical in high volume manufacturing due to frequency mismatches

Engineering Contradiction:

Improvefrequency matching precisionVSAvoidmanufacturing complexity

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

The patent implements a tunable notch filter with a frequency adjustment mechanism that allows the filter center frequency to be dynamically tuned to match the actual first mode frequency of each MEMS scanner. This dynamic adjustment capability resolves the contradiction by enabling precise frequency matching without requiring complex manufacturing processes, as the filter can be adapted to individual device variations.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes the parameter of the notch filter from a fixed center frequency to a tunable center frequency that can be adjusted to match the first mode frequency. This parameter change allows the system to accommodate manufacturing variations while maintaining effective suppression of first mode oscillations, thus resolving the contradiction between manufacturing precision and ease of manufacture.

Inventive Principle:

Principle #35Parameter changes

2Object-generated harmful factors

If a low pass filter is used to attenuate first mode oscillations, then the oscillations are suppressed, but the vertical sweep waveform is distorted causing visible distortion at the top and bottom of the raster

Engineering Contradiction:

Improvefirst mode oscillationsVSAvoidwaveform accuracy

Core Design Contradiction:

Object-generated harmful factorsVSManufacturing precision

Solution Approach 1:

The patent applies a notch filter with a narrow bandwidth that is specifically targeted at the first mode frequency, rather than using a broad low pass filter. This local quality approach suppresses only the harmful first mode oscillations while preserving the integrity of the vertical sweep waveform at other frequencies, thus eliminating the waveform distortion problem.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent employs a feedback mechanism that uses the sensor output signal to adjust the notch filter settings, ensuring that the filter is precisely tuned to the actual first mode frequency. This feedback approach allows for accurate suppression of oscillations without affecting the overall waveform shape, maintaining waveform accuracy while eliminating harmful oscillations.

Inventive Principle:

Principle #23Feedback

3Manufacturing precision

If the number of horizontal sweep lines is reduced to avoid distorted regions, then waveform distortion is avoided, but the productivity of the projection system decreases

Engineering Contradiction:

Improveimage qualityVSAvoidprojection throughput

Core Design Contradiction:

Manufacturing precisionVSProductivity

Solution Approach 1:

The patent converts the harmful effect of first mode oscillations into a controllable parameter by using a tunable notch filter. Instead of reducing the number of sweep lines to avoid distortion, the system actively suppresses the oscillations, allowing full utilization of the available sweep lines and maintaining high projection throughput while ensuring image quality.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 approach effectively suppresses first mode oscillations, resulting in a uniform raster image without distortion, even in high volume manufacturing environments where precise frequency matching is challenging.

Implementation Method 1

a phase-compensated feedback loop that self-tunes to precisely match the MEMS first mode frequency

Methodology Applied

Scientific EffectFeedback: Feedback

Implementation Method 2

the resonant mode associated with horizontal sweep is beneficial. Unfortunately, the mirror has multiple resonant modes for both vertical and horizontal movement

Methodology Applied

Scientific EffectResonance: Resonance

Data Source

PatentUS8059322B1System for suppressing undesirable oscillations in a MEMS scanner

Publication Date: 2011.11.15 NAT SEMICON CORP

AI summary

A system for suppressing undesirable oscillations in a micro-electro-mechanical system (MEMS) scanner is provided. The system includes a tunable notch filter and a MEMS scanner. The tunable notch filter is operable to receive an original drive signal and to generate a compensated drive signal based on the original drive signal. The MEMS scanner, which is coupled to the tunable notch filter, is operable to receive the compensated drive signal and to be driven by the compensated drive signal without oscillating at a first mode resonance frequency.