Mutual capacitance variation measuring circuit with high precision and low power consumption

Abstract

The invention relates to a mutual capacitance variation measuring method with a high precision and a high stability. The system is composed of a switch discharge current source, a voltage follower and an impulse generator. The impulse generator generates an impulse waveform with a fixed length of time so that a detected mutual capacitance on a high clock edge is charged. If a voltage of a detected end is more than a reference voltage, the switch discharge current source discharges so as to reduce the voltage of the detected end until the voltage is lower than the reference voltage.<{EN4}>As for different discharge time periods of a switch current source caused by different detected mutual capacitances, the variation of the detected capacitances can be detected through measuring the variation of the time periods or the ratio variation of the time periods.<{EN5}>An error accumulation and mutual elimination method is applied by the circuit so that effects of an impact of a voltage fluctuation, an error of a measuring clock and an error of a detecting circuit itself on a measuring result are minimized to a lowest point. Therefore, the measuring method is great in measuring precision and stability. Because of the error accumulation and mutual elimination, the detecting circuit does not need a circuit with the high precision, and thus a simple circuit with the low power consumption can be adopted to realize. As for different discharge time periods of a switch current source caused by different detected mutual capacitances, the variation of the detected capacitances can be detected through measuring the variation of the time periods or the ratio variation of the time periods. An error accumulation and mutual elimination method is applied by the circuit so that effects of an impact of a voltage fluctuation, an error of a measuring clock and an error of a detecting circuit itself on a measuring result are minimized to a lowest point. Therefore, the measuring method is great in measuring precision and stability. Because of the error accumulation and mutual elimination, the detecting circuit does not need a circuit with the high precision, and thus a simple circuit with the low power consumption can be adopted to realize.

Description

technical field [0001] The invention relates to a mutual capacitance measuring circuit with high precision and low power consumption 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. Especially suitable for multi-finger touch detection. Background technique [0002] The basic principle of the traditional mutual capacitance touch detection is to use the pulse generator to periodically charge and discharge the measured mutual capacitance, and use the current conversion circuit to copy the charging and discharging current to an internal filter capacitor, and through the detection of the filter capacitor The voltage value is used to judge the change of the measured mutual capacitance. If there is no touch, its voltage is V1. If you touch the measured mutual capacitance with a finger or a touch pen, since many magnetic force lines will stay on the finger, the m...

AI Technical Summary

Problems solved by technology

[0003] The disadvantages of the traditional detection method are: 1) Larger chip internal filter capacitors are required to ensure its stability, and the chip needs to occupy a larger area to realize these filter capacitors, so that the final chip area becomes larger and the cost increases; 2) Chip The detection of the internal voltage must use a high-speed and high-precision ADC, which will increase the area and power consumption of the chip.

3) Due to the fact that the consistency of the measured mutual capacitance and PCB parameters is difficult to guarantee in practical applications, this leads to a large variation range of the measured voltage and even exceeds the constraints of the power supply voltage, making the measurement fail, so the control and adjustment of mass production is difficult

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