Touch Sensing Device Double Sampling Method Noise Reduction
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Solution Overview
Problem
Mutual capacitive touch screens face challenges in distinguishing touch points due to increased noise levels, particularly high frequency noise, DC offset, and interference, which reduce the signal-to-noise ratio (SNR) and sensitivity, especially with multi-touch inputs.
Innovation Solution
A touch sensing device with a double sampling method that includes a touch screen with Tx and Rx lines, a Tx driving circuit supplying a driving signal multiple times, and an Rx driving circuit that double samples signals using a multiplexer and integrator to accumulate and invert signal polarities, effectively improving the SNR by canceling out noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a mutual capacitive touch screen is used to sense multi-touch inputs, then the touch sensing capability is improved, but noise increases and signal-to-noise ratio decreases
Solution Approach 1:
The patent applies periodic action by driving Tx lines multiple times (N times where N≥2) and performing multiple sampling operations. The touch sensor output is sampled at different time points during the driving period, and these samples are integrated to produce a final output signal. This periodic sampling and integration approach separates the touch signal from noise that occurs at different frequencies, thereby improving signal-to-noise ratio while maintaining multi-touch sensing capability.
Solution Approach 2:
The patent implements preliminary action through the integrator circuit that accumulates multiple sampled signals before final output. By pre-integrating the sampled signals during the driving period, the system prepares a refined signal that has already had noise components filtered out through the integration process, before the final readout occurs.
2Measurement precision
If multiple Tx lines and Rx lines are used to enable multi-touch detection, then touch point discrimination capability is improved, but interference between channels increases
Solution Approach 1:
The patent reduces channel interference by implementing periodic driving and sampling. Each Tx line is driven multiple times with periodic sampling performed on the Rx lines. This time-division approach with multiple sampling points allows the system to distinguish between signals from different touch points and interference from adjacent channels, improving touch point discrimination while reducing crosstalk.
Solution Approach 2:
The integration process acts as a feedback mechanism where multiple samples taken during the driving period are accumulated and averaged. This feedback loop allows the system to identify and cancel out periodic interference patterns that occur between channels, thereby improving the accuracy of touch point discrimination in multi-touch scenarios.
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
The double sampling method enhances the signal-to-noise ratio by accumulating signal voltages of the same polarity, reducing noise, and improving touch point discrimination, especially in multi-touch scenarios.
Implementation Method 1
an integrator configured to sample and integrate the first and second signals received from the multiplexer
Data Source
AI summary
A touch sensing device includes a touch screen including Tx lines, Rx lines crossing the Tx lines, and touch sensors formed at crossings of the Tx lines and the Rx lines, a Tx driving circuit for supplying a driving signal to each of the Tx lines N times, where N is a positive integer equal to or greater than 2, and an Rx driving circuit for double sampling signals received through the Rx lines in one period of the driving signal. The Rx driving circuit includes a multiplexer which receives first and second signals and switches on or off a signal transmission path of the first and second signals, and an integrator which samples and integrates the first and second signals received from the multiplexer.