Touch Sensor Circuit for Simultaneous Pen and Multi-Touch Sampling
Find Innovative SolutionsGenerate Solutions
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 simultaneous transmission and reception of multiple frequencies across multiple channels, enabling simultaneous sampling of self, mutual, and pen touch signals, while employing 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 with switches and integrators are used to measure mutual capacitance, then measurement can be performed, but parasitic capacitances of the switch are large compared to the mutual capacitances (measured in fractions of a pico-farad), requiring 200 or more integration cycles to overcome noise, which increases sample time to 1 ms or more
Solution Approach 1:
The patent extracts and eliminates the problematic switch component from the sensing circuitry. By using a resistive divider network instead of switches to control signal routing, the parasitic capacitance is dramatically reduced since resistors have negligible parasitic capacitance compared to switches. This allows the system to achieve accurate mutual capacitance measurements without requiring hundreds of integration cycles, thereby reducing sample time from 1 ms or more to a much shorter duration.
Solution Approach 2:
The patent replaces the mechanical/electronic switch-based signal routing mechanism with a resistive divider-based system. The resistive dividers provide continuous, passive signal attenuation and routing without the need for active switching elements. This substitution eliminates the parasitic capacitance bottleneck that limited measurement speed, allowing faster sampling while maintaining measurement precision.
2Measurement precision
If multiple integration cycles are performed to overcome parasitic capacitance effects, then measurement accuracy improves, but the length of time to make a determination increases with the number of electrodes that must be measured, affecting user experience on large displays
Solution Approach 1:
The patent removes the switch component that introduced high parasitic capacitance, replacing it with a resistive divider network. This extraction of the problematic element allows the system to achieve the necessary measurement accuracy without relying on multiple slow integration cycles, thereby improving touch response speed while maintaining precision across large numbers of electrodes.
Solution Approach 2:
The patent changes the fundamental parameter of the sensing circuit from high-impedance switch-based coupling to low-impedance resistive divider-based coupling. This parameter change in the circuit topology fundamentally alters the time constant and noise characteristics, enabling faster sampling rates that can handle large displays without compromising measurement accuracy.
3Measurement precision
If self capacitance measurement is used to determine touch location, then the signal-to-noise ratio is much larger than mutual capacitance, but self parasitic capacitances are large because surrounding channels are effectively grounded, and only one signal is driven at a time
Solution Approach 1:
The patent implements a unified resistive divider network that serves multiple functions simultaneously: it enables both self-capacitance and mutual-capacitance measurement modes without requiring separate circuit paths or complex switching arrangements. The same resistive infrastructure supports driven channels and sense channels, allowing flexible signal routing and simultaneous multi-channel operation, thereby reducing device complexity while maintaining high signal-to-noise ratio.
4Object-affected harmful factors
If surrounding channels are grounded to reduce noise in self capacitance measurement, then noise is reduced, but self parasitic capacitances increase and only one signal can be driven at a time
Solution Approach 1:
The patent extracts the grounding requirement by using the resistive divider network to provide natural noise filtering through its voltage division and impedance matching properties. The resistive network inherently rejects common-mode noise and interference without requiring channels to be grounded, thereby eliminating the bottleneck that limited signal processing throughput and enabled only single-channel operation at a time.
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 enhances the speed, resolution, and sensitivity of touch sensor data acquisition, allowing for faster and more accurate multi-touch detection across various sensor types and configurations, while reducing noise and improving user experience on large displays.
Implementation Method 1
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 2
Sense circuitry coupled to the electrodes of the other orientation (e.g., the horizontal electrodes or sense electrodes) measures current flow between the electrodes due to mutual capacitive coupling that exists between the column electrodes and the row electrodes
Implementation Method 3
the integrator may integrate the signal measured on the sense electrode over two hundred or more cycles, which could take 1 ms or more for a drive pulse with a frequency of 200 kHz
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.