Touch Sensor Pixel Circuit for High-Resolution Low-Noise Sensing
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Solution Overview
Problem
Existing touch sensors face limitations in resolution and size due to parasitic capacitance, which affects signal-to-noise ratio and integration into electronic devices, making it difficult to achieve high-resolution, large-area touch sensing.
Innovation Solution
A sensor array with each pixel comprising a capacitive sensing electrode and a reference capacitor, along with a voltage-controlled impedance (VCI) that modulates impedance in response to a control voltage, reducing parasitic capacitance and improving signal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If passive matrix capacitive touch sensing is used, then device complexity is reduced, but measurement precision deteriorates due to sensitivity to environmental noise and interference
Solution Approach 1:
A differential amplifier circuit is introduced as an intermediary between the capacitive sensing electrode and the readout circuit. This differential amplifier actively suppresses environmental noise and interference by amplifying only the differential signal from the touch sensor, thereby improving measurement precision without significantly increasing device complexity
Solution Approach 2:
The patent implements a feedback mechanism where the output of the differential amplifier is fed back to adjust the driving signal to the capacitive sensing electrode. This feedback loop compensates for environmental variations and noise, maintaining high measurement precision while using a relatively simple passive matrix structure
2Measurement precision
If active matrix capacitive touch sensors are used, then measurement precision is improved, but device complexity increases due to switching elements in each pixel
Solution Approach 1:
The patent extracts the active switching function from individual pixels and relocates it to a separate row-column scanning circuit. This allows the pixel structure to remain simple while still achieving active matrix performance, reducing device complexity while maintaining measurement precision
Solution Approach 2:
A differential amplifier circuit is introduced as an intermediary that compensates for the lack of per-pixel switching elements. This amplifier provides the necessary signal conditioning and noise rejection that would otherwise require complex switching circuits in each pixel
3Measurement precision
If more pixels are combined in parallel to increase resolution, then measurement precision is improved, but parasitic capacitance increases additively limiting sensor size
Solution Approach 1:
A differential amplifier circuit is introduced as an intermediary between the parallel pixel array and the readout circuit. This amplifier has high input impedance that isolates the parasitic capacitance effects from the signal path, allowing more pixels to be combined in parallel to increase resolution without the parasitic capacitance limiting factor
Solution Approach 2:
The patent transitions from series connection to parallel connection of pixel columns, utilizing the differential amplifier to manage the increased capacitance load. This dimensional change in circuit topology allows scaling to higher resolutions by adding more pixels rather than increasing pixel size
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 resolution and size capability of touch sensors by minimizing parasitic capacitance and noise, enabling high-resolution biometric touch sensing over larger areas.
Implementation Method 1
capacitive sensing electrode for accumulating a charge in response to proximity of a conductive object to be sensed
Implementation Method 2
a reference capacitor connected in series with the capacitive sensing electrode so that, in response to a control voltage, an indicator voltage is provided at the connection between the reference capacitor and the capacitive sensing electrode
Data Source
AI summary
A sensor array (10) comprising a plurality of touch sensitive pixels, each pixel (12) comprising a capacitive sensing electrode (14) and a reference capacitor (16) connected in series with the capacitive sensing electrode (14) to provide an indicator voltage that is indicative of the proximity of a conductive object to be sensed.