Capacitance Sensor FIR Filtering for Touch Noise Rejection
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Solution Overview
Problem
Surface capacitive touch screens face challenges in accurately sensing capacitance changes due to noise interference, requiring effective noise filtering to distinguish user inputs from unwanted signals.
Innovation Solution
A capacitance sensor system comprising a capacitance-voltage/current converter, a multiplier, and an accumulator, which converts capacitance values into voltage or current signals, applies weights to output signals, and accumulates them, functioning as a finite impulse response (FIR) filter to filter out noise and emphasize specific signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If noise filtering is applied to distinguish user inputs from unwanted signals, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The signal processing is divided into distinct functional stages: capacitance-to-voltage/current conversion, weighted multiplication, and accumulation. Each stage is implemented by separate circuit blocks (capacitance-voltage/current converter, multiplier, accumulator), allowing independent optimization and reducing overall system complexity while maintaining high measurement precision through staged noise filtering.
Solution Approach 2:
The capacitor is periodically charged and discharged in synchronized cycles. During the charging phase, the capacitor accumulates charge proportional to the input capacitance value. During the discharging phase, the stored charge is converted to voltage/current signals and processed. This periodic operation enables time-domain signal separation and facilitates noise filtering through temporal sampling.
2Reliability
If multiple switches and capacitors are used for noise filtering, then reliability is improved, but ease of operation worsens
Solution Approach 1:
Multiple switches (first switch controlling input connection, second switch controlling ground connection, third switch for alternative grounding) are merged into a coordinated control system that operates in synchronized phases. The switches work together as an integrated switching network rather than independent components, reducing the operational burden by providing unified control logic for what would otherwise be multiple separate control functions.
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 system effectively filters noise, allowing for accurate detection of capacitance changes caused by user inputs, enhancing the sensitivity and reliability of touch screen devices by emphasizing desired signals and reducing interference.
Implementation Method 1
a capacitance-voltage/current converter which converts a capacitance value of a sense capacitor into a voltage signal or a current signal
Implementation Method 2
a first amplifier; a second amplifier
Data Source
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AI summary
Disclosed is a capacitance sensor including: a capacitance-voltage/current converter which converts a capacitance value of a sense capacitor into a voltage signal or a current signal by using an input signal; a multiplier which applies a weight to an output signal of the capacitance-voltage/current converter and outputs the weighted output signal; and an accumulator which accumulates continuously the output signal of the multiplier.