Self-capacitance change measuring circuit with quick response

Abstract

The invention relates to a method for quickly detecting capacitance change, which comprises the following steps of: utilizing a detecting circuit to quickly charge a detected capacitor (2) and a filter capacitor (1) at the beginning, thereby establishing a capacitor initial voltage based on a reference voltage Vref; utilizing a current source (6) to charge the filter capacitor (1) while utilizing a switch capacitance circuit to discharge, wherein the switch capacitance circuit is formed by the detected capacitor (2), a switch (3) and a switch (4); after the voltage on the filter capacitor (1) reaches a stable value after a period of time, utilizing a phase-reversal switch capacitance amplifier (9) to amplify a difference value between the voltage of the filter capacitor (1) and the reference voltage Vref; and utilizing an analog-to-digital converter (10) to acquire an output voltage value of the amplifier. When the detected capacitor (1) changes, the voltage on the filter capacitor (1) also changes, and the results acquired by the ADC (analog-to-digital converter) are different. By analyzing the result change of the ADC, the instant relative change of the detected capacitor (1) can be acquired.

Description

technical field [0001] The present invention relates to a self-capacitance change measuring circuit with fast response and an implementation method in an integrated circuit. The method can be used in touch control applications, such as touch keys, capacitive touch screens, mouse touch pads and other wide-ranging applications. Background technique [0002] The basic principle of traditional capacitive touch-sensitive keys is a relaxation oscillator that is constantly charged and discharged. If there is no touch, the relaxation oscillator has a fixed charge-discharge cycle and the frequency can be measured. If the button area is touched with a finger or other object, the dielectric constant of the distributed capacitance of the button will increase, the charging and discharging cycle will become longer, and the frequency will decrease accordingly. By measuring the change in period, the touch action can be detected. [0003] The prior art method has no voltage buffer amplifi...

AI Technical Summary

Problems solved by technology

[0004] Its disadvantages are: 1) The input signal of the voltage analog-to-digital converter changes from zero, and it takes a long time to stabilize, thus affecting the time required for each detection; 2) The filter capacitor cannot be increased arbitrarily, otherwise the single-slope voltage Analog-to-digital converters overflow, limiting noise immunity

3) This method is susceptible to electromagnetic interference, resulting in misoperation

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