Touch detection method of mutual capacitance touch screen

Abstract

The invention discloses a touch detection method of a mutual capacitance touch screen. The method comprises collecting noise signals of each reception channel, conducting spectral analysis on the noise signals and finding out a frequency point with the minimum power under the condition of sending no excitation signal; sequentially sending excitation signals generated at selected frequency points of each reception channel to the touch screen through a drive circuit; converting charge transmitted from a capacitor to be detected through a charge amplifier into voltage signals simultaneously by each reception channel, simultaneously forming a first-order high-pass filter by using the charge amplifier, filtering low-frequency interference signals, using an analog-digital converter to convert electrical signals into digital signals, respectively mixing the digital signals and sinusoidal signals and cosine signals which are generated at the selected frequency points after filtering the digital signals, conducting coherent integration on output of a mixer, obtaining a range of a coherent integration result to serve as a final measured value, and judging whether touch exists or not by detecting changes of the measured value. The method is good in noise immunity, low in harmonic interference, small in use of storage resources and high in computational accuracy.

Description

technical field [0001] The invention relates to the field of smart phones, in particular to a touch detection method of a mutual capacitance touch screen. Background technique [0002] The surface of the mutual capacitive touch screen is a horizontal electrode array and a vertical electrode array made of ITO. Such as figure 1 As shown, the place where the two sets of electrodes intersect will form a capacitor, that is, the two sets of electrodes respectively constitute the two poles of the capacitor. When a finger touches the capacitive screen, it affects the coupling between the two electrodes near the touch point, thereby changing the capacitance between the two electrodes. When detecting the mutual capacitance, the vertical electrodes send excitation signals sequentially, and all the horizontal electrodes receive signals simultaneously, so that the capacitance value at the intersection of all horizontal and vertical electrodes can be obtained, that is, the capacitance v...

AI Technical Summary

Problems solved by technology

[0008] 1. In order to simplify the circuit, a square wave is usually used as the excitation signal. This method will generate a lot of harmonic interference such as image 3 As shown, multiple transmitting electrodes become antennas for transmitting harmonic interference, which will generate a large amount of harmonic interference to the system itself and other devices in the application, and this interference is especially serious in mobile phones

[0009] 2. In the process of mixing the received signal, the generation of the carrier at the selected frequency adopts the look-up table method (LUT). The accuracy of this method is limited by the depth and width of the look-up table, and it needs to occupy a large number of storage units.

[0010] 3. The frequency selection of the excitation signal usually depends on the empirical value, and cannot cope with the noise interference in different environments

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