CN105591642A

CN105591642A - Capacitive sensing relaxation oscillator

Info

Publication number: CN105591642A
Application number: CN201410552341.XA
Authority: CN
Inventors: 曾庆东
Original assignee: Individual
Current assignee: Individual
Priority date: 2014-10-19
Filing date: 2014-10-19
Publication date: 2016-05-18

Abstract

The invention discloses a capacitive sensing relaxation oscillator, which comprises at least one touching capacitor, a comparator, a pulse width modulator, a counter, a reference clock and a reference voltage, wherein the touching capacitor detection end and the reference voltage output end are respectively connected with the positive phase input end and the reverse phase input end of the comparator; the output end of the comparator is connected with the input end of the pulse width modulator; and the input end of the pulse width modulator and the input end of the reference clock are respectively connected with the signal input end and the clock input end of the counter. The capacitive sensing relaxation oscillator also comprises a reset switch connected between the positive phase input end of the comparator and the ground line, wherein the control end of the reset switch is connected with the output end of the comparator. According to the capacitive sensing relaxation oscillator, tiny changes of a finger capacitor are amplified by using the relaxation oscillator, and while the signals are amplified, the anti-interference performance of a capacitor touching signal is improved, and the possibility of error judgment is reduced.

Description

Capacitive sensing relaxation oscillator

Technical field

The present invention relates to electronic circuit field, particularly, relate to a kind of capacitive sensing relaxation oscillator.

Background technology

Touch sensor has been widely used a lot of years. But the development of mixed signal programming device, allows capacitive touch sensors become one practicality, the appreciation type replacement scheme of mechanical switch in various consumption electronic products in the recent period.

The typical tectal thickness of capacitance type sensor is 3mm or thinner. Along with the increase of overburden cover, it is more and more difficult that the sensing of finger touch will become. The core of any capacitance touch sensor-based system is all one group and the interactional conductor of electric field. In tissue below human body skin, being full of conductive electrolyte---this is that one damages dielectric. This conductive characteristic of finger makes capacitance touch sensing become possibility just.

Simple plane-parallel capacitor has two conductors, between these two conductors across one deck dielectric. Most of energy in this system is directly gathered between capacitor plate. A little energy can be leaked to the space beyond capacitor plate, and the electric field being formed by these leakage energy is called fringing field. A part difficult problem of making practical capacitance type sensor is to design a set of printed circuit board traces, and fringing field is directed in the accessible actual induction of user region. Plane-parallel capacitor is not the ideal chose of this mode sensor. In the time that finger is placed near fringe field, the conductive surface area of capacitive sensing system can increase. By the additional charge memory capacity that produces of finger, be exactly the finger capacitor C F known to us.

Summary of the invention

In the time that multiplication factor increases, easily cause the technological deficiency of erroneous judgement for solving existing capacitance type sensor parser circuitry, the invention discloses a kind of capacitive sensing relaxation oscillator.

Capacitive sensing relaxation oscillator of the present invention, comprise that at least one touches electric capacity, also comprise comparator, pulse width modulator, counter and reference clock and reference voltage, touching capacitance detecting end is connected with normal phase input end and the inverting input of comparator respectively with reference voltage output end, the output of described comparator connects the input of pulse width modulator, the input of described pulse width modulator and reference clock is signal input part and the input end of clock of linkage counter respectively, also comprise the reset switch being connected between comparator normal phase input end and ground wire, the control end of described reset switch is connected with comparator output terminal.

Preferably, between the normal phase input end of described comparator and power supply, be connected with pull-up current source.

Preferably, also comprise signal selecting bus, more than one of described touch electric capacity, touches electric capacity and is connected between signal transmission bus and ground, the output of described signal selecting bus connects comparator normal phase input end, the multi-channel analog selector switch that described signal selecting bus is programming Control.

Preferably, described reference clock frequency is 24M.

Concrete, described reset switch is NMOS pipe, control end is grid.

Capacitive sensing relaxation oscillator of the present invention, utilizes relaxation oscillator to amplify to the minor variations of finger electric capacity, in amplifying signal, has improved the anti-interference of capacitance touch signal, has reduced the probability that erroneous judgement occurs.

Brief description of the drawings

Fig. 1 is a kind of detailed description of the invention schematic diagram of the present invention.

Detailed description of the invention

Below in conjunction with embodiment and accompanying drawing, the present invention is done to detailed description further, but embodiments of the present invention are not limited to this.

Capacitive sensing relaxation oscillator of the present invention, comprise that at least one touches capacitor C N, also comprise comparator C OMP, pulse width modulator, counter and reference clock and reference voltage V TH, touching capacitance detecting end is connected with normal phase input end and the inverting input of comparator respectively with reference voltage output end, the output of described comparator connects the input of pulse width modulator, the input of described pulse width modulator and reference clock is signal input part and the input end of clock of linkage counter respectively, also comprise the reset switch being connected between comparator normal phase input end and ground wire, the control end of described reset switch is connected with comparator output terminal.

The output of comparator is sent to the clock input circuit of pulse-width modulator (PWM), and 16 digit counters that this PWM is 24MHz to a clock frequency carry out gate. Finger above sensor increases electric capacity, and then causes count value to increase. The existence of finger detects based on this principle.

Preferably, also comprise signal selecting bus, more than one of described touch electric capacity, touches electric capacity and is connected between signal transmission bus and ground, the output of described signal selecting bus connects comparator normal phase input end, the multi-channel analog selector switch that described signal selecting bus is programming Control. Select successively each to touch the capacitance variations value of electric capacity with certain sense cycle.

Preferably, described reference clock frequency is 24M.

Concrete, described reset switch is NMOS pipe, control end is grid.

As mentioned above, can realize preferably the present invention.

Claims

1. capacitive sensing relaxation oscillator, comprise that at least one touches electric capacity, it is characterized in that, also comprise comparator, pulse width modulator, counter and reference clock and reference voltage, touching capacitance detecting end is connected with normal phase input end and the inverting input of comparator respectively with reference voltage output end, the output of described comparator connects the input of pulse width modulator, the input of described pulse width modulator and reference clock is signal input part and the input end of clock of linkage counter respectively, also comprise the reset switch being connected between comparator normal phase input end and ground wire, the control end of described reset switch is connected with comparator output terminal.

2. capacitive sensing relaxation oscillator according to claim 1, is characterized in that, is connected with pull-up current source between the normal phase input end of described comparator and power supply.

3. capacitive sensing relaxation oscillator according to claim 1, it is characterized in that, also comprise signal selecting bus, more than one of described touch electric capacity, touching electric capacity is connected between signal transmission bus and ground, the output of described signal selecting bus connects comparator normal phase input end, the multi-channel analog selector switch that described signal selecting bus is programming Control.

4. capacitive sensing relaxation oscillator according to claim 1, is characterized in that, described reference clock frequency is 24M.

5. capacitive sensing relaxation oscillator according to claim 1, is characterized in that, described reset switch is NMOS pipe, and control end is grid.