Capacitive Sensor Test Circuit Voltage Compensation

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Solution Overview

Problem

Existing methods for testing electronic circuits with capacitive sensors are limited by their dependence on supply voltage variations and inability to programmatically adjust electrostatic forces, leading to non-linear output voltages and inefficiencies in emulating physical quantities like force, acceleration, and pressure.

Innovation Solution

An automatic testing method that generates a constant reference voltage using a bandgap voltage multiplied by stored factors, independent of supply voltage variations, to adjust electrostatic forces in capacitive sensors, allowing for precise programming of test forces and minimizing additional electronic components.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Force

If a single fixed electrode is biased to high voltage during test phase to generate electrostatic force, then the force can be generated to test the sensor, but the generated force depends on supply voltage variations causing non-linear output

Engineering Contradiction:

Improveelectrostatic forceVSAvoidoutput voltage linearity

Core Design Contradiction:

ForceVSMeasurement precision

Solution Approach 1:

The patent changes the voltage parameter from a fixed supply voltage to a dynamically adjusted voltage that compensates for supply variations. The test voltage is calculated as Vtest = Vsupply - Voffset, where Voffset is determined from the measured output voltage during normal operation. This parameter adjustment ensures that the electrostatic force remains constant despite supply voltage fluctuations, resolving the non-linearity issue.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent implements a feedback mechanism where the output voltage measured during normal sensor operation is used to determine the offset voltage. This feedback loop allows the system to automatically compensate for supply voltage variations by adjusting the test voltage accordingly, ensuring consistent electrostatic force generation during testing.

Inventive Principle:

Principle #23Feedback

2Productivity

If supply voltage is used directly to bias the fixed electrode during testing, then the testing can be performed, but the electrostatic force varies with supply voltage fluctuations

Engineering Contradiction:

Improvetesting efficiencyVSAvoidforce consistency

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent performs preliminary measurement of the output voltage during normal sensor operation before the actual force generation test. This preliminary action allows the system to calculate the appropriate offset voltage in advance, ensuring that the subsequent electrostatic force will be consistent and independent of supply voltage variations.

Inventive Principle:

Principle #10Preliminary action

3Ease of manufacture

If parasitic capacitors are present in the integrated sensor circuit, then the circuit can be integrated on semiconductor substrate, but non-linearities are introduced in the output voltage

Engineering Contradiction:

Improvecircuit integrationVSAvoidoutput voltage linearity

Core Design Contradiction:

Ease of manufactureVSMeasurement precision

Solution Approach 1:

The patent replaces the mechanical/physical approach of minimizing parasitic capacitors through careful layout with an electrical compensation approach. Instead of trying to eliminate parasitic effects through mechanical design, the system uses voltage compensation based on feedback to cancel out the non-linearities introduced by parasitic capacitors.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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

The method ensures electrostatic forces generated during testing are independent of supply voltage fluctuations, enabling accurate and efficient testing of capacitive sensors with programmable forces, reducing the impact of parasitic capacitors and improving measurement linearity.

Implementation Method 1

generates a constant reference voltage using a bandgap voltage multiplied by stored factors

Methodology Applied

Scientific EffectBandgap voltage:

Implementation Method 2

electronic circuit with a capacitive sensor... two capacitors mounted in differential having a common electrode capable of moving between two fixed electrodes

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 3

A test phase makes it possible to generate a deliberately controlled electrostatic force by polarizing only one of the fixed electrodes of the two capacitors

Methodology Applied

Scientific EffectElectrostatic force: Electrostatics

Data Source

PatentEP1962063B1Automatic test of an electronic circuit for a capacitive sensor, and electronic circuit for carrying out said test

Publication Date: 2010.11.17 EM MICROELECTRONIC-MARIN

Figure 1
Figure 2~4
Figure 3

AI summary

The method involves dividing measuring cycles into two successive phases (P1, P2) in a normal operating mode. Capacitors (C1, C2) are discharged by an output voltage provided by an integrator unit (5) in the phase (P1). Electrodes of the capacitors of differential mounted capacitors are polarized by high or low voltage of a voltage source in another phase. A polarizing voltage is obtained on a basis of a constant reference voltage that is programmed as a function of a desired electrostatic force to be generated for an automatic test of an electronic circuit (1). An independent claim is also included for an electronic circuit with a capacitive sensor suited for implementing an automatic test method.