Touch Sensor Circuit for Simultaneous Self and Mutual Detection
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Solution Overview
Problem
Current multi-touch systems face challenges in simultaneous sampling of different modes such as self, mutual, and pen capacitance, leading to increased sample time and user experience issues, especially on large displays, due to high parasitic capacitances and noise interference from salt water contamination.
Innovation Solution
The implementation of a circuitry system using voltage-following sigma-delta A/D converters and sigma-delta D/A converters that allow for simultaneous transmission and reception of multiple frequencies across multiple channels, enabling simultaneous sampling of self, mutual, and pen touch signals, while using digital I/O pins and external passive filters to reduce noise and parasitic capacitance effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional sense circuits measure mutual capacitance by repetitively switching sense electrodes to an integrator, then measurement can be performed, but parasitic capacitances of the switch are large compared to mutual capacitances requiring many integration cycles
Solution Approach 1:
The patent combines self-capacitance measurement and mutual-capacitance measurement into a single integrated circuit that performs both measurements simultaneously. The sense circuit is configured to measure self-capacitance of drive electrodes while also measuring mutual-capacitance between drive and sense electrodes, eliminating the need for separate measurement cycles and reducing total measurement time.
Solution Approach 2:
The patent changes the measurement parameter by using self-capacitance measurement as an additional or alternative parameter to mutual-capacitance measurement. By measuring self-capacitance of drive electrodes, the system obtains touch information through a different electrical parameter that is less affected by parasitic capacitances, thereby improving measurement speed and accuracy.
2Measurement precision
If multiple integration cycles are performed to overcome parasitic capacitance effects, then measurement accuracy improves, but the time to determine touch location increases
Solution Approach 1:
The patent merges self-capacitance measurement and mutual-capacitance measurement into a single operational cycle. The sense circuit simultaneously measures both self-capacitance of drive electrodes and mutual-capacitance between drive and sense electrodes, providing accurate touch location data without requiring multiple sequential measurement cycles.
Solution Approach 2:
The patent enables continuous measurement by configuring the sense circuit to continuously monitor both self-capacitance and mutual-capacitance parameters. This continuous measurement approach maintains accurate touch detection without the need for repeated integration cycles, thereby improving touch detection speed while maintaining accuracy.
3Productivity
If self-capacitance measurement is used to overcome parasitic capacitance issues, then measurement speed improves, but salt water contamination affects the measurement
Solution Approach 1:
The patent combines self-capacitance measurement and mutual-capacitance measurement results to compensate for salt water contamination effects. By comparing and processing both measurement types simultaneously, the system can distinguish between genuine touch signals and noise caused by salt water contamination, maintaining measurement accuracy in contaminated environments.
Solution Approach 2:
The patent uses feedback processing to analyze both self-capacitance and mutual-capacitance measurement results. The system processes the combined data to identify and filter out contamination-induced noise, providing accurate touch detection even in the presence of salt water contamination while maintaining fast measurement speed.
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 approach significantly reduces sample time, enhances resolution and sensitivity, and improves noise rejection, allowing for faster and more accurate touch detection across various touchscreen types and configurations, including those with salt water contamination.
Implementation Method 1
voltage-following sigma-delta A/D converters combined with sigma-delta D/A converters that allow for simultaneous transmission and reception of multiple frequencies across multiple channels
Implementation Method 2
the location is determined by sensing changes in capacitances to and between the electrodes
Implementation Method 3
The mutual capacitance between the intersection of a column electrode and a row electrode will change when a user touches the substrate in the vicinity of the intersection
Implementation Method 4
The sense circuitry measures current flow changes to the electrodes due to electrodes self-capacitive coupling that exists between the driven electrode and impedance paths to ground
Implementation Method 5
digital I/O pins and external passive filters to reduce noise and parasitic capacitance effects
Data Source
AI summary
A touch sensor circuit includes a plurality of drive/receive circuits and a drive signal generation circuit. The drive/receive circuits drive and receive signals from a multi-touch sensor. A drive/receive circuit includes an analog to digital conversion (ADC) circuit and a digital to analog conversion (DAC) circuit. The ADC circuit includes a first input to receive a sensor signal on an electrode of the multi-touch sensor. The sensor signal includes a drive signal component and a receive signal component. The ADC circuit includes a second input to receive an analog reference signal from the drive signal generation circuit. The ADC circuit generates a digital signal based on the analog reference signal and the sensor signal. The DAC circuit converts the digital signal into the drive signal component and the receive signal component is representative of an impedance on the electrode detected and is indicative of a touch proximal to the electrode.