Analog Front-End Channel Driver for Fast, Low-Noise 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 driven onto 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 determination time increases
Solution Approach 1:
The patent extracts and eliminates the parasitic capacitance component from the measurement signal through differential measurement techniques. By using a reference electrode that experiences the same parasitic capacitance as the sensing electrode, the system subtracts out the parasitic effect, allowing accurate touch detection with fewer integration cycles, thus reducing determination time while maintaining precision.
Solution Approach 2:
The system implements feedback through the differential measurement process, where the reference electrode signal is continuously compared with the sensing electrode signal. This feedback mechanism allows the system to quickly identify and compensate for parasitic capacitance variations, enabling faster convergence to an accurate touch location determination without requiring multiple slow integration cycles.
2Object-affected harmful factors
If multiple integration cycles are performed, then noise reduction is improved, but processing time increases
Solution Approach 1:
The differential measurement approach extracts and removes noise components that are common to both the sensing and reference electrodes. By subtracting the reference signal from the sensing signal, the system eliminates environmental noise and interference, achieving effective noise reduction without requiring multiple slow integration cycles, thus maintaining high processing speed.
3Device complexity
If parasitic capacitances are not compensated, then device complexity is reduced, but measurement precision deteriorates
Solution Approach 1:
The patent introduces a reference electrode as an intermediary element that experiences the same parasitic capacitance as the sensing electrode. This reference electrode acts as a mediator that allows the system to measure and compensate for parasitic effects without adding complex compensation circuits. The differential measurement using this intermediary achieves high precision while maintaining relatively simple device architecture.
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 reduced noise interference.
Implementation Method 1
a differential module configured to receive a reference signal and configured to generate an analog error signal based on a channel driving signal and the reference signal
Implementation Method 2
incorporates noise shaping to reduce noise interference
Implementation Method 3
generate a low impedance virtual signal driven onto a load while receiving and outputting load-modified signals
Implementation Method 4
enables faster and more accurate determination of touch locations by reducing the impact of parasitic capacitances
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.