Amplifier Circuit for Piezo Sensor Parasitic Signal Neutralization
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Solution Overview
Problem
Existing measurement amplifier circuits for piezoelectric sensors in internal combustion engines fail to accurately amplify pressure signals due to parasitic signals caused by non-identical parasitic capacitive elements, leading to measurement distortion.
Innovation Solution
A measurement amplifier circuit with a common mode voltage generation module connected to the engine wall, featuring a high-pass filter and EMC filters, which generates a common mode voltage signal to neutralize parasitic charges by maintaining a fixed voltage across parasitic capacitive elements, thereby eliminating parasitic signal interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional differential amplifier circuit is used to amplify the piezoelectric sensor signal, then the signal amplification function is achieved, but parasitic signals from non-identical parasitic capacitive elements cause measurement distortion
Solution Approach 1:
The patent introduces a common mode voltage generation module as an intermediary component between the sensor and the differential amplifier. This module generates a common mode voltage signal that is applied to both inputs of the differential amplifier, serving as a mediator to counteract the asymmetric parasitic signals. The common mode voltage acts as a compensating signal that neutralizes the effect of non-identical parasitic capacitive elements, thereby eliminating measurement distortion while preserving the signal amplification function.
Solution Approach 2:
The patent changes the voltage parameter applied to the parasitic capacitive elements by introducing a dynamically adjusted common mode voltage. Instead of using a fixed ground reference, the system varies the common mode voltage level to match and counteract the parasitic signal variations. This parameter change transforms the static parasitic effect into a compensatable dynamic condition, allowing the differential amplifier to reject the parasitic signals while amplifying the true pressure signal.
2Length of moving object
If the spacing between sensor terminals and cylinder wall is reduced, then the sensor fits better in the combustion chamber, but parasitic capacitive elements are created causing signal distortion
Solution Approach 1:
The patent converts the harmful parasitic capacitive effects into a beneficial condition by using the same parasitic capacitance to generate a useful common mode signal. Instead of trying to eliminate the parasitic capacitance caused by reduced spacing, the system harnesses it to create a common mode voltage that naturally counteracts the parasitic signal interference. This approach transforms the geometric constraint (reduced spacing) from a source of error into a feature that can be exploited for signal compensation.
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 solution effectively suppresses parasitic signals, ensuring accurate measurement of pressure peaks without distortion, as evident from the improved output signal curves that no longer show variations from parasitic charges.
Implementation Method 1
a first parasitic signal Sp1 and a second parasitic signal Sp2 corresponding to parasitic charges are respectively superimposed on the first signal Sc1 and the second signal Sc2 delivered by the sensor 100... where C1 is the electrical capacitance of a first parasitic capacitive element 120... where C2 is the electrical capacitance of a second parasitic capacitive element 130... Said parasitic capacitive elements 120, 130 are created by a reduced spacing between an internal wall 111 of cylinder 110 of the motor and terminals 101, 102 of sensor 100
Implementation Method 2
The sensor 100 measures the pressure in a combustion chamber of the engine. Said piezoelectric pressure sensor 100 delivers a signal Sc to be measured... This signal Sc to be measured is differential and corresponds to an electric charge proportional to the pressure prevailing in the combustion chamber
Data Source
Figure 1~2
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Figure 5~6
AI summary
A measurement amplifying circuit (400) for a piezo-electric sensor (100) positioned in an internal combustion engine supplying a signal to be measured, includes: a module (420) for generating a common mode voltage; a differential amplifier (410); and a subtraction module (430). The module (420) for generating a common mode voltage is to be connected to a wall (111) of the engine, the module (420) for generating a common mode voltage being suitable for supplying a common mode voltage signal (Vcm) reproducing the variations of an engine signal (Sb) received from the wall (111) of the engine.