Capacitive Touchscreen Charge Acquisition Circuit Noise Immunity
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Solution Overview
Problem
Capacitive touchscreen systems face challenges in achieving low drive voltages while maintaining high noise immunity, as high voltage drive signals are typically required to minimize power dissipation and system noise, which are contradictory objectives.
Innovation Solution
A capacitive touchscreen system with a configuration of electrically conductive drive and sense electrodes arranged at angles, utilizing a charge acquisition circuit with a charge storage capacitor and switches to charge and discharge electrodes in phases, allowing mutual capacitance to be measured effectively with low voltage drive signals, thereby reducing power consumption and noise interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high voltage drive signals are used, then power dissipation is reduced and system noise immunity is improved, but power consumption increases
Solution Approach 1:
The patent employs periodic switching of drive electrodes between drive voltage and ground through controlled phases. Switches alternately connect drive electrodes to drive voltage (charging phase) and ground (discharge phase), creating periodic action that enables mutual capacitance measurement without requiring sustained high voltage, thus reducing power consumption while maintaining noise immunity during measurement windows.
Solution Approach 2:
The patent pre-charges mutual capacitance during a first phase before measurement by connecting drive electrodes to drive voltage. This preliminary charging action stores energy in the mutual capacitance, which is then measured during subsequent phases without requiring continuous high voltage supply, thereby reducing overall power consumption while maintaining the ability to detect capacitance changes with high signal-to-noise ratio.
2Object-affected harmful factors
If high voltage drive signals are used, then system noise immunity is improved, but power dissipation increases
Solution Approach 1:
The system uses periodic switching sequences where drive electrodes are connected to drive voltage only during specific charging phases and disconnected during other phases. This periodic action creates concentrated measurement windows with high signal levels for noise immunity, while minimizing the duration of high voltage application to reduce power dissipation. The alternating connection to ground during discharge phases further reduces average power consumption.
Solution Approach 2:
The patent extracts the essential measurement function from continuous high voltage operation by isolating measurements to specific time windows where drive electrodes are temporarily connected to drive voltage. This extraction allows the system to achieve high noise immunity only when needed for measurement, while removing unnecessary continuous high voltage that would increase power dissipation, effectively separating the measurement function from sustained high voltage operation.
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 enables high signal-to-noise ratio and low power consumption by doubling the effective signal during each readout cycle without the need for high drive voltages, effectively addressing the noise immunity and power dissipation issues in capacitive touchscreen systems.
Implementation Method 1
a charge acquisition circuit comprising a charge storage capacitor arranged in parallel with a fifth switch
Implementation Method 2
each drive electrode being operably connected to a third switch and a fourth switch, the third switch being configured to operably connect the drive electrode to a drive voltage, the fourth switch being configured to operably connect the drive electrode to ground
Data Source
AI summary
Various embodiments of capacitive touchscreen driving and sensing circuits are disclosed, where during a first phase the mutual capacitance between a given drive electrode and a given sense electrode is charged up to a first charge value corresponding substantially to a drive voltage times the mutual capacitance. During a second phase the charge storage capacitor is charged up to a value corresponding approximately to a difference in touchscreen capacitance network charges occurring during the first and second phases. The first and second phases do not overlap in time. Dark frame signals may also be acquired from the touchscreen to calibrate differences in touchscreen capacitance network charges.