Self-capacitance change measuring circuit with high precision and high stability

Abstract

The invention relates to a self-capacitance change measuring circuit with high precision and high stability. A filter capacitor in a system discharges through a switch circuit of a measured capacitor and is charged through a switch circuit of a coupling capacitor so as to change the voltage of the filter capacitor at the vicinity of a reference voltage. As discharging current generated by the switch circuits of different measured capacitors is different, the time that the voltage of the filter capacitor is lower than the reference voltage and the time that the voltage of the filter capacitor is higher than the reference voltage change; and the change of the measured capacitor can be measured by measuring the time change or the change of a ratio of the time. By an error elimination method, the voltage fluctuation and the metering clock error do not influence the measuring result; and the entire measuring result is only related to the error of the coupling capacitor. As the coupling capacitor built in a chip has high stability and high precision, the measurement method has excellent measuring precision and stability.

Description

technical field [0001] The invention relates to a self-capacitance measuring circuit with high precision and high stability and a realization method thereof. The method can be used in touch control applications, such as touch buttons, capacitive touch screens, mouse touch pads and the like. Background technique [0002] The basic principle of traditional capacitive touch-sensing buttons is a relaxation oscillator that is continuously charged and discharged. If there is no touch, the relaxation oscillator has a fixed charge and discharge cycle, and the frequency can be measured. If you touch the measured object with a finger or a touch pen, the dielectric constant of the capacitor will increase, the charging and discharging cycle of the capacitor will become longer, and the frequency will decrease accordingly. By measuring the change of the period, the touch action can be detected. This method is susceptible to electromagnetic interference, poor measurement accuracy and st...

AI Technical Summary

Problems solved by technology

This method is susceptible to electromagnetic interference, poor measurement accuracy and stability, and prone to misoperation

[0003] The disadvantages of the traditional detection method 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 converter would overflow, limiting noise immunity

3) Due to the difficulty in ensuring the consistency of capacitance and PCB parameters in practical applications, it is difficult to control and adjust mass production 4) It is easily affected by factors such as power supply voltage fluctuations and clock source jitter

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