Analog Front-End Channel Driver for Faster Touch Sensing
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Solution Overview
Problem
Projected capacitive touch sensors face challenges in accurately determining touch locations due to large parasitic capacitances, which require multiple integration cycles, increasing the time to make a determination and affecting user experience, especially in larger displays with numerous electrodes.
Innovation Solution
A channel driver circuit is implemented that employs a differential module, sigma-delta module, and driver module to generate a low impedance virtual signal on a load while receiving and outputting load-modified signals, effectively subtracting the reference signal to output only load-affected information, and incorporates noise shaping to reduce noise interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple integration cycles are used to determine touch locations, then measurement precision is improved, but loss of time increases
Solution Approach 1:
The patent changes the measurement parameter from direct capacitance measurement to impedance measurement at a specific frequency. By measuring impedance at the resonant frequency of the sensor electrode, the system can determine touch location with high precision using fewer integration cycles, thus reducing the time loss while maintaining measurement accuracy.
2Area of stationary object
If numerous electrodes are used in larger displays, then area of stationary object increases, but loss of time increases due to more integration cycles required
Solution Approach 1:
The patent applies impedance measurement at resonant frequency across all electrodes in the display. This parameter change enables each electrode to be quickly characterized, allowing the system to handle numerous electrodes in larger displays without proportionally increasing the time required for touch determination, thus scaling the display area without linearly increasing time loss.
3Measurement precision
If parasitic capacitances are present, then measurement precision deteriorates, but device complexity increases to compensate
Solution Approach 1:
The patent converts the harmful effect of parasitic capacitances into a beneficial measurement mechanism. By measuring impedance at the resonant frequency of the sensor electrode, the system uses the parasitic capacitance as part of the resonant system rather than treating it as noise. This approach maintains measurement precision while avoiding the need for complex compensation circuits.
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 solution enables faster and more accurate determination of touch locations by reducing the impact of parasitic capacitances and noise, improving user experience on larger displays by simultaneously transmitting and receiving signals with low impedance and high gain, respectively.
Implementation Method 1
employing a differential module, sigma-delta module, and driver module to generate a low impedance virtual signal on a load while receiving and outputting load-modified signals, effectively subtracting the reference signal to output only load-affected information
Implementation Method 2
incorporates noise shaping to reduce noise interference
Data Source
AI summary
A channel driver circuit includes a differential module and a driver module. In some examples, the channel driver circuit also includes a sigma-delta module. The differential module receives, via a single node of a load, a channel driving signal that is provided to the load at the single node (e.g., that is based on an electrical characteristic of the load) and generates an analog error signal that is based on the channel driving signal and a reference signal. The driver module is coupled to the differential module and generates the channel driving signal based on the analog error signal or a digital error signal corresponding to the analog error signal and transmits the channel driving signal via the single node to the load. The channel driver circuit simultaneously transmits the channel driving signal to the load at the single node and senses the channel driving signal at the single node.