Display Touch Detection Guard Signal Parasitic Capacitance
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Solution Overview
Problem
In display devices with capacitive touch detection, parasitic capacitance caused by the crossover of self-capacitance detection and signal lines interferes with the detection process, particularly in self-capacitive sensing, leading to reduced detection accuracy.
Innovation Solution
The display device employs a scanning line drive circuit that adjusts the number of scanning lines supplied during different frames to match the potential of the touch detection period, using a guard signal to reduce parasitic capacitance and improve detection accuracy by synchronizing the potentials across frames.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If self-capacitance detection line and signal connection line cross each other to enable touch detection function, then touch detection capability is achieved, but parasitic capacitance increases and detection accuracy deteriorates
Solution Approach 1:
A guard signal line is introduced as an intermediary element between the self-capacitance detection line and the signal connection line. This guard signal line acts as a shield to reduce the parasitic capacitance coupling between the crossing lines, thereby maintaining both the touch detection capability and the detection accuracy without requiring changes to the basic line crossover configuration
2Measurement precision
If guard signal is applied to reduce parasitic capacitance, then detection accuracy is improved, but device complexity increases
Solution Approach 1:
The guard signal line is merged with the existing signal connection line infrastructure by using the same physical line to carry both the signal and the guard signal at different time periods. This integration approach reduces the need for completely separate additional wiring, thereby limiting the increase in device complexity while still achieving the parasitic capacitance reduction benefit
3Object-affected harmful factors
If scanning lines are adjusted between frames to match potential, then parasitic capacitance is reduced, but driving complexity increases
Solution Approach 1:
The scanning lines are driven with periodic alternating signals at different frequencies during different frame periods. By adjusting the scanning frequency to match or mismatch the touch detection frequency in an alternating pattern, the potential differences between scanning lines and detection lines are synchronized periodically, which reduces the parasitic capacitance effect through constructive interference cancellation
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 effectively minimizes parasitic capacitance, enhancing the accuracy and reliability of touch detection in display devices with capacitive sensing, reducing noise and improving overall performance.
Implementation Method 1
a detection method which uses occurrence of a change of an electrostatic capacitance between a pair of electrodes (referred to as a drive electrode and a detection electrode) by approach or contact of an input object
Implementation Method 2
self capacitive sensing, the drive electrode also serves as the detection electrode which detects approach or contact of the object
Implementation Method 3
the self-capacitance detection line and the connection line which supplies the signal to the video signal line cross each other, and a parasitic capacitance produced by this crossover constitutes a load at a driving operation by the self capacitive sensing
Data Source
AI summary
According to one embodiment, a display device includes a display portion, a touch detection circuit and a scanning line drive circuit. A frame period, which includes a display period in which the scanning signal is supplied to the plurality of scanning lines for image display, and a touch detection period related to sensing using the plurality of electrodes, includes a first frame and a second frame. The number of scanning lines to which the scanning signal is supplied in each display period included in the first and second frames is adjusted such that a potential of the touch detection period included in the first frame matches a potential of the touch detection period included in the second frame.