Touch Detection Chip Impedance Adjustment for Water Drop Noise
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Solution Overview
Problem
Existing touch screen detection technologies face challenges in distinguishing between small difference values caused by external noise and water drops due to saturation issues in differential programmable gain amplifiers, leading to low signal-to-noise ratio and sensitivity.
Innovation Solution
A touch detection chip with an impedance-adjustable circuit that offsets partial AC signals, allowing for a larger amplifying coefficient and improving signal-to-noise ratio and sensitivity by adjusting the impedance value to prevent saturation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If only DC component is introduced to non-inverting input end of PGA to subtract DC component from driving signal, then DC offset is removed, but larger AC component remains causing PGA saturation and reducing amplifying coefficient
Solution Approach 1:
The patent extracts and removes the AC component from the driving signal separately from the DC component. By introducing a second AC signal through the non-inverting input end of the PGA that is opposite in phase to the AC component of the driving signal, the AC components cancel each other out, leaving only the DC component to be processed by the PGA. This prevents PGA saturation and allows for higher amplifying coefficients.
Solution Approach 2:
The patent applies preliminary anti-action by introducing an opposite-phase AC signal before the PGA processing stage. The second AC signal is designed to be opposite in phase to the AC component of the driving signal, so that when they combine at the non-inverting input end, the AC components cancel each other out in advance, preventing saturation before it occurs in the PGA.
2Reliability
If amplifying coefficient of PGA is set small to avoid saturation, then PGA works in linear range, but detected difference value becomes small making it difficult to distinguish from noise
Solution Approach 1:
The patent extracts the harmful AC component from the driving signal and removes it through phase cancellation before it reaches the PGA. By introducing an opposite-phase AC signal through the non-inverting input end, the AC components cancel out, allowing the PGA to operate with a larger amplifying coefficient without saturation, thereby improving the detected difference value and signal to noise ratio.
3Measurement precision
If alternate coding detection is used with odd channel floating, then water drop detection is enabled, but AC component coupling through water drop causes signal distortion
Solution Approach 1:
The patent converts the harmful AC signal coupling effect into a beneficial cancellation mechanism. By deliberately introducing a second AC signal through the non-inverting input end that is opposite in phase to the coupled AC signal, the system transforms the harmful coupling effect into a useful phase cancellation that eliminates the distorted AC component while preserving the water drop detection capability.
Data Source
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AI summary
The present disclosure relates to the field of detection technology, and provides a touch detection chip and a touch screen detection method. The touch detection chip includes: a signal output unit configured to output a driving signal to a first channel of a touch screen in a water drop detection mode; a first analog front end circuit, an inverting input end of which being connected to the first channel; a second analog front end circuit, an inverting input end of which being connected to a second channel of the touch screen, wherein the second channel is adjacent to the first channel and the second channel is left floating in the water drop detection mode; an impedance-adjustable circuit connected between a non-inverting input end of the first analog front end circuit and the signal output unit; a DC voltage unit connected to a non-inverting input end of the second analog front end circuit; and a processing unit separately connected to the signal output unit, an output end of the first analog front end circuit, and an output end of the second analog front end circuit. In the present disclosure, a signal-to-noise ratio and sensitivity of the touch screen detection can be improved to some extent.