Optical Mouse Drive Circuit Impedance Measurement

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Solution Overview

Problem

Conventional optical mice face performance issues on smooth or transparent surfaces and require different parts and design efforts for LED and laser-based models, increasing inventory costs and complexity.

Innovation Solution

A universal control circuit that automatically determines the type of light source connected by measuring impedance, adjusting the current source accordingly, and ensuring eye safety by selecting appropriate current ranges based on impedance measurements.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a universal control circuit measures impedance to automatically determine light source type and adjust current, then device complexity and inventory requirements are reduced, but measurement precision and reliability are required to correctly distinguish between LED and laser diode connections

Engineering Contradiction:

Improvecontrol circuit complexityVSAvoidimpedance measurement precision

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent applies parameter changes by measuring impedance at multiple different current levels (at least two distinct current values) to characterize the light source. This multi-point measurement approach changes the operating parameter (current) to gather sufficient data for reliable light source identification and safe operating current determination, resolving the contradiction between simplified control and measurement precision requirements.

Inventive Principle:

Principle #35Parameter changes

2Ease of operation

If the controller automatically adjusts current based on impedance measurements, then ease of operation is improved, but the risk of harmful effects (eye safety) increases if measurements are inaccurate

Engineering Contradiction:

Improveautomatic current adjustmentVSAvoideye safety

Core Design Contradiction:

Ease of operationVSObject-affected harmful factors

Solution Approach 1:

The patent implements feedback by continuously monitoring impedance at multiple current levels and using this information to automatically adjust and limit the current to safe levels. The controller uses the measured impedance characteristics to feedback control the current, ensuring that even if the light source type is misidentified, the current remains within safe operating limits, thus protecting against eye damage while maintaining ease of operation.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent applies beforehand cushioning by establishing maximum safe current limits based on impedance measurements before harmful effects can occur. The system proactively determines safe operating parameters through preliminary impedance characterization and sets current ceilings that prevent excessive current flow, cushioning against potential eye safety hazards before they can materialize.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

3Adaptability or versatility

If impedance measurement is used to identify light source type, then adaptability is improved, but device complexity increases due to additional measuring circuitry

Engineering Contradiction:

Improvelight source compatibilityVSAvoidmeasuring circuit complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent applies universality by designing a control circuit that can universally handle both LED and laser diode light sources through impedance measurement. The same control circuitry performs multiple functions: measuring impedance, identifying light source type, determining safe current limits, and controlling current output. This multi-functional approach increases adaptability while managing device complexity through functional integration rather than separate dedicated circuits for each light source type.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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

Enables consistent performance across different surfaces and reduces manufacturing costs by eliminating the need for separate components for LED and laser-based mice, while ensuring eye safety through automatic current adjustments.

Implementation Method 1

a potential measuring circuit that generates a signal indicative of a drive circuit potential between the first and second ports

Methodology Applied

Scientific EffectElectrical Impedance: Electrical Resistance

Data Source

PatentUS7737949B2Driving circuit adapted for use in optical mice

Publication Date: 2010.06.15 PIXART IMAGING INC

AI summary

A control circuit having a drive circuit and a controller adapted for use in optical mice is disclosed. The drive circuit is connected between first and second ports and passes a current between those ports having an amplitude determined by a control signal that is generated by the controller. The first port is connected to an illumination device and the second port is connected to a power rail. The control circuit also includes a potential measuring circuit that generates a signal indicative of a drive circuit potential between the first and second ports. The controller records the drive circuit potential for a predetermined current when the first port is connected to an illumination device. The controller sets the control signal based on the recorded drive circuit potential. The control circuit can record the drive circuit potential when the controller is powered.