Mutual capacitance detecting circuit

Abstract

The invention discloses a mutual capacitance detecting circuit. The mutual capacitance detecting circuit comprises a current limiting transmitter module, a first capacitor and a receiving module. The current limiting transmitter module enables the first capacitor output alternatively positive and negative current under the control of clock signals; the receiving module comprises a current transmission module and an ADC (analog / digital converter) module, the ADC module comprises a second capacitor, a comparator and a counter, the current transmission module rectifies and transmits current output by the first capacitor to the first electrode plate of the second capacitor, and the voltage of the first electrode plate of the second capacitor reverses the output level of the comparator; the counter counts the width of the reversed level and outputs digital level pulse signals with a corresponding width. The mutual capacitance detecting circuit reduces the amplitude and the bandwidth of current signals through the current limiting transmitter module, reduces the requirements on an amplifier through current transmission, restrains the influence of common-mode noise, outputs a high signal to noise ratio under the condition of a low input signal to noise ratio and improves the detecting sensitivity.

Description

technical field [0001] The invention relates to the technical field of circuit design, in particular to a mutual capacitance detection circuit used on a capacitive touch device. Background technique [0002] Among existing capacitive touch detection devices, devices based on mutual capacitance detection can realize real multi-touch, but compared with self-capacitance detection, mutual capacitance detection needs to face problems such as low input signal-to-noise ratio and high system cost. [0003] figure 1 It is an existing mutual capacitance detection circuit, and the detection circuit calculates the coordinates of each touch point by detecting the power change data of the two-dimensional capacitance of the touch screen when the finger is touched. Its working principle is as follows: When there is no touch, the external excitation VIN jumps from one voltage V1 to another voltage V2, and by controlling the on and off of the first switch S1, the negative feedback of the fir...

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Problems solved by technology

[0004] At the same time, when touching with human hands, there is a common-mode noise leakage path due to the lack of common ground between the human body and the detection system. Therefore, capacitive detection is an electrical open detection (all references are not based on the same ground reference). Poor common mode rejection

When human touch is performed, the self-capacitance change due to the proximity of the human hand to the detection sensor is generally 10-100 times the mutual capacitance change. Common-mode noise is released through this self-capacitance coupling. In some amplifiers with poor common-mode noise , the input signal-to-noise ratio can easily be reduced to 1 / 1-1 / 10

At the same time, technological evolution and the use of the stylus have aggravated the deterioration of the input signal-to-noise ratio and increased the requirements for the detection signal-to-noise ratio. In order to solve these problems, if the common mode noise of the amplifier is reduced and the detection chip itself performs ASP (Analog Signal Process, analog signal processing) or DSP (Digital Signal Process, digital signal processing) filtering and other methods will bring high system cost

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