Capacitive Position Detector Noise Cancellation via Differential Amplifier
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Solution Overview
Problem
Position detectors using electrostatic capacitance systems face challenges in accurately detecting finger positions due to noise interference from the human body, which cannot be effectively canceled by traditional differential amplifiers.
Innovation Solution
A position detector configuration with a conductor pattern divided into three electrode lines, where the central electrode line is connected to the positive input of a differential amplifier, and the outer lines are connected to the negative input, allowing for effective noise cancellation from the human body.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional differential amplifiers are used for noise cancellation, then noise filtering is provided, but noise from the human body cannot be effectively canceled
Solution Approach 1:
The reception electrode line is divided into three separate electrode lines (first, second, and third lines). This segmentation allows the system to capture noise signals from different positions and combine them to cancel out human body interference, thereby improving detection precision while addressing the limitation of traditional single-line differential amplifiers.
Solution Approach 2:
The patent combines signals from multiple electrode lines (first, second, and third lines) through a signal processing circuit. By merging these signals in a specific configuration where the second line's signal is subtracted from the first and third lines, the system achieves effective cancellation of human body noise while maintaining detection accuracy.
2Measurement precision
If electrode lines are arranged in a matrix for position detection, then position information can be obtained, but noise interference increases
Solution Approach 1:
The patent applies different functional qualities to different parts of the electrode system. Transmission electrode lines provide AC signals for detection, while reception electrode lines are specifically configured with three separate lines for noise cancellation. This local differentiation allows the system to maintain position detection capability while reducing noise interference in critical measurement areas.
Solution Approach 2:
The signal processing circuit acts as an intermediary that processes signals from multiple electrode lines. It combines and differentiates signals in a specific manner, mediating between the raw electrode signals and the final detection output, thereby eliminating human body noise while preserving position information.
3Measurement precision
If the detected current is converted to voltage and amplified, then the weak current becomes detectable, but noise is also amplified
Solution Approach 1:
The system performs preliminary noise cancellation by configuring the electrode lines and signal processing circuit to subtract noise signals before final amplification. By arranging the first, second, and third electrode lines in a specific configuration and processing their signals accordingly, the system eliminates human body noise in advance, preventing it from being amplified along with the useful signal.
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 configuration enhances the precision of finger position detection by canceling noise interference, ensuring accurate signal processing and reliable operation of the position detector.
Implementation Method 1
a differentially amplifying circuit having first and second input terminals for differentially amplifying signals inputted thereto through the first and second input terminals, respectively
Implementation Method 2
the position information detecting technique, using an electrostatic capacitance system, for detecting a position in accordance with a change in electrostatic capacitance of a film on a surface of a detection planar surface
Data Source
AI summary
A capacitive type position detector is provided, which includes a conductor pattern formed of a plurality of conductors disposed in a first direction and in a second direction intersecting with the first direction; a transmission signal supplying circuit for supplying a transmission signal to said plurality of conductors disposed in the first direction; and a differentially amplifying circuit having first and second input terminals for amplifying signals inputted thereto. The differentially amplifying circuit is configured to receive signals from a set of at least three conductors among said plurality of conductors disposed in the second direction, to thereby receive signals from the conductors located on both end sides of the set via said first input terminal and to receive a signal(s) from the conductor(s), which is(are) located between said conductors located on both end sides of the set, via said second input terminal.