CN102193033B - Self-capacitance change measuring circuit with quick response - Google Patents

Self-capacitance change measuring circuit with quick response Download PDF

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Publication number
CN102193033B
CN102193033B CN201010118932.8A CN201010118932A CN102193033B CN 102193033 B CN102193033 B CN 102193033B CN 201010118932 A CN201010118932 A CN 201010118932A CN 102193033 B CN102193033 B CN 102193033B
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China
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voltage
switch
filter capacitor
phase
circuit
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CN201010118932.8A
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Chinese (zh)
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CN102193033A (en
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贾朝辉
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上海海栎创微电子有限公司
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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

A kind of self-capacitance change measuring circuit with response fast

Technical field

The present invention relates to a kind of self-capacitance change measuring circuit with response fast, and implementation method in integrated circuits.The method may be used in touch control application, and such as touch key-press, capacitive touch screen, in the widespread uses such as mouse touch pad.

Background technology

The ultimate principle of traditional capacitance touch induced key is exactly the relaxor of a constantly charging and discharging.If when not touching, relaxor has a fixing charging discharging cycle, and frequency can be measured.If with finger or other object touch key-press region, will increase the specific inductive capacity of the distributed capacitance of button, charging discharging cycle is just elongated, and frequency will correspondingly reduce.The change of measuring period, just can detect touch action.

Original technical method does not have voltage buffer amplifier, adopts comparer, the oscillation period of timer measuring oscillator, or adopts single-slope voltage analog-digital quantizer to detect change oscillation period.

Its shortcoming is: 1) input signal of voltage analog-digital quantizer is started from scratch change, needs the long period to stablize, thus has influence on the time required for each detection; 2) filter capacitor can not strengthen arbitrarily, otherwise single-slope voltage analog-digital quantizer can overflow, thus limits antijamming capability.3) this method is easily subject to electromagnetic interference (EMI), produces misoperation.

Summary of the invention

The object of the present invention is to provide a kind of method for detecting capacitance change of quick response, can be used in the application such as touch control.For reaching above object, solution of the present invention is:

By a voltage buffer, at beginning detection-phase, quick pre-charging electricity is carried out to measured electric capacity and filter capacitor, make electric capacity initial voltage be based upon in reference voltage Vref; Then the switch utilizing a current source and controlled by pulse producer for a pair, to filter capacitor discharge and recharge; Through certain hour reach or close to balance after, utilize a phase-veversal switch dielectric amplifier, the difference of voltage on filter capacitor to reference voltage Vref is amplified, and utilize one fast analogue-to-digital converters (ADC) obtain magnitude of voltage conversion value.When measured electric capacity changes time, the voltage on filter capacitor can change, and by the judgement changed magnitude of voltage, can analyze the transient change of measured electric capacity, so that subsequent treatment.

Owing to have employed such scheme, the present invention has following characteristics: 1) time of each Detection capacitance change is short, reduces system latency time; 2) antijamming capability is strong, utilizes filter capacitor to reduce the interference of outside instantaneous noise to measurement result; 3) utilize phase-veversal switch dielectric amplifier amplify one relative to the input voltage of Vref reference voltage and be transformed into relative to one, ground output voltage, thus take full advantage of the effective voltage working range of 0V to supply voltage; 4) circuit is simple, easily realizes on the integrated.Only need the filter capacitor that outside, all the other all can be on the integrated integrated.

Accompanying drawing explanation

The system chart of Fig. 1 testing circuit

Fig. 2 phase-veversal switch dielectric amplifier internal circuit

Fig. 3 testing circuit is at the equivalent circuit diagram of pre-charging stage

Fig. 4 testing circuit is at the equivalent circuit diagram in filter capacitor discharge and recharge stage

The signal input part of Fig. 5 phase-veversal switch dielectric amplifier and output terminal are in the change in voltage of measuring period

The change of the applied signal voltage caused during Fig. 6 capacitance variations

Embodiment

Below in conjunction with accompanying drawing illustrated embodiment, the present invention is further illustrated.

Fig. 1 is the ultimate system circuit diagram of metering circuit.A measuring period of this metering circuit can be divided into three steps, respectively:

1) filter capacitor electric capacity pre-charging stage

In FIG, cut-off switch (5) and switch (3), Closing Switch (4) and switch (7), carry out the level of rapid charge to reference voltage Vref by voltage buffer to filter capacitor and measured capacitance.As shown in Figure 3, the signal input part of phase-veversal switch dielectric amplifier and the voltage waveform of output terminal change t0 ~ t1 stage as shown in Figure 5 to its equivalent electrical circuit.Now and be indifferent to the output valve of phase-veversal switch dielectric amplifier.

2) the filter capacitor continuous discharge and recharge stage

In FIG, cut-off switch (7), Closing Switch (5), the complementary pulse produced by pulse producer exports driving switch (4) and switch (3), and phase-veversal switch dielectric amplifier works on simultaneously.Under the pulse of certain frequency exports driving, switch (3), switch (4) and measured electric capacity (2) equivalence can become a resistance (R), and the inverse of the product of its resistance size and pulsed frequency and measured capacitance size is relevant.By adjusting the switching frequency of pulse producer, the resistance size of equivalent resistance can be adjusted, thus adapt to different measured capacitance.

As shown in Figure 4, the signal input part of phase-veversal switch dielectric amplifier and the voltage waveform of output terminal change t1 ~ t2 stage as shown in Figure 5 to its equivalent electrical circuit.Now still be indifferent to the output valve of phase-veversal switch dielectric amplifier.

By adjustment current source (6), be equivalent to adjust the electric current flowing through equivalent resistance, thus the voltage on filter capacitor can be adjusted, obtain correct amplifier input voltage range.

3) the voltage measurement stage

Through after a period of time, namely the t3 point shown in Fig. 5, when switch (5) and switch (4) tie point, the i.e. signal input part of phase-veversal switch dielectric amplifier, its voltage Vin reaches or close to stationary value Va, now change in voltage trend comparison is smooth.

The difference DELTA V=(Vref-Va) of Va and reference voltage, after the multiple (N) of amplifier amplifies, obtains the voltage of N* (Vref-Va) at output terminal.This voltage is fed to analogue-to-digital converters fast and measures, and obtains measured capacitance reading.

Phase-veversal switch dielectric amplifier output voltage values Vout is:

Vout=N*(Vref-Va)

Wherein Va is amplifier input signal magnitude of voltage, and N is the enlargement factor of amplifier.

Fig. 5 is signal input part and the change in voltage situation of output terminal within a measuring period of phase-veversal switch dielectric amplifier.

Owing to adopting following methods, this circuit has capacitance variations response fast:

1) adopt voltage buffer to carry out rapid charge to reference voltage Vref to filter capacitor and measured capacitance, shorten the time of pre-charging stage.Then on this basis, by discharge circuit, make the voltage on filter capacitor only decline hundreds of millivolt just arrive burning voltage, thus shorten the time of discharge regime.

2) adopt fast analog-todigital converter to carry out analog to digital conversion fast to through amplifying signal, avoid the longer switching time adopted needed for single-slope voltage analog-digital quantizer.

Specifically when doing touch and detecting, because external circuit exists certain distributed capacitance, this distributed capacitance is metastable.Therefore, in the frequency of given pulse producer, under the conditions such as constant current source output valve and filter capacitor size, the voltage of the signal input part of amplifier is when discharge regime reaches balance, and magnitude of voltage is stabilized near Va.If external circuit changes, such as, have finger contact that distributed capacitance is changed, now the equivalent capacity of external circuit will increase, and when discharge regime reaches balance, the applied signal voltage value of amplifier will become Va ', referring to Fig. 6.The electric capacity transient change of external circuit can be reflected from the reading result of ADC, thus the changes such as the contact of finger detected.By after the processor that connects does certain data processing (such as digital filtering), and rational threshold value is set, when the data variation of the ADC result read is greater than threshold value time, the contact of exterior object can be judged as.

Should be understood that; concerning the those of ordinary skill in field, place of the present invention; can carry out corresponding equivalent change according to technical scheme of the present invention and design thereof or replace, and all these change or replace, and all should belong to the protection domain of claims of the present invention.

The present invention, except in the application that can be used in touch detection, also may be used for proximity test, in the application of other sensors such as liquid position detection.These application are all in protection scope of the present invention.

Claims (7)

1. one kind has the self-capacitance change measuring circuit of response fast, for detecting fast the capacitance variations on the tested circuit in outside, described circuit comprises filter capacitor (1), pulse producer (11) and corresponding on-off circuit, adjustable current source (6), phase-veversal switch dielectric amplifier (9) and Fast simulation one digital quantizer (10), it is characterized in that: by a voltage buffer (8), at beginning detection-phase, quick pre-charging electricity is carried out to measured capacitance (2) and filter capacitor (1), the initial voltage of filter capacitor (1) and measured capacitance (2) is made to arrive reference voltage Vref fast, then utilize adjustable current source (6) to filter capacitor (1) charging, discharged by measured capacitance (2) and the complementary switch that controlled by pulse producer (11) for a pair simultaneously, stationary value is reached through the upper voltage of post filtering electric capacity (1) after a while, utilize phase-veversal switch dielectric amplifier (9), the difference of the voltage on filter capacitor (1) and reference voltage Vref is amplified, and utilizes fast analog-todigital converter (10) to obtain phase-veversal switch dielectric amplifier output voltage values, when measured capacitance (2) changes, voltage on filter capacitor (1) also can change, the result that fast analog-todigital converter obtains also can be different, by the analysis changed fast analog-todigital converter Result, obtain the instantaneous relative variation of measured capacitance.
2. circuit according to claim 1, comprise an adjustable current source (6), output terminal sequentially passes through charge switch (5), charge balance switch (4) and electric charge bleed off switch (3) and receives ground level, it is characterized in that:
1) tie point of charge switch (5) and charge balance switch (4) also receives the non-ground-end of a filter capacitor (1);
2) tie point of charge balance switch (4) and electric charge bleed off switch (3) also receives the non-ground-end of measured capacitance (2);
3) adjustable current source output valve is adjusted within the specific limits, to adapt to the measurement needs of different measured capacitance size.
3. circuit according to claim 1, comprises a voltage buffer, it is characterized in that:
1) output terminal of voltage buffer accesses the tie point of charge switch (5) and charge balance switch (4) through voltage buffer switch (7);
2) input end of voltage buffer is received in reference voltage Vref, by the strong driving effect of voltage buffer, the voltage fast driving on filter capacitor is arrived reference voltage Vref.
4. circuit according to claim 1, comprises a phase-veversal switch dielectric amplifier (9), it is characterized in that:
1) phase-veversal switch dielectric amplifier (9) is for amplifying the difference of the voltage on filter capacitor (1) and reference voltage Vref;
2) enlargement factor of phase-veversal switch dielectric amplifier (9) is adjusted within the specific limits, to adapt to the measurement needs of different measured capacitance size;
3) output terminal of phase-veversal switch dielectric amplifier (9) directly or access a fast analog-todigital converter (10) by voltage buffer.
5. circuit according to claim 1, comprises a pulse producer, it is characterized in that:
1) pulse producer exports the signal for two-way complementation, drives charge balance switch (4) and electric charge bleed off switch (3) respectively;
2) by the alternate conduction to electric charge bleed off switch (3) and charge balance switch (4), the electric discharge of filter capacitor (1) is controlled;
3) by adjustment pulse producer pulsed frequency, adjustment discharge current size, to adapt to the measurement needs of different measured capacitance size.
6. circuit according to claim 1, comprise a fast analog-todigital converter (10), it is characterized in that: the input of fast analog-todigital converter directly or is indirectly received in the output of phase-veversal switch dielectric amplifier (9), the output voltage of phase-veversal switch dielectric amplifier (9) is detected fast.
7. circuit according to claim 1, is characterized in that the measurement that measured capacitance changes comprises the steps:
1) when starting detection-phase, measured capacitance in parallel and filter capacitor, or only connect filter capacitor, utilize voltage buffer to carry out quick pre-charging electricity, make the initial voltage of filter capacitor arrive reference voltage Vref;
2) then off voltage impact damper, utilizes an adjustable current source and a pulse producer, makes measured capacitance alternately receive filter capacitor and ground level, make filter capacitor do discharge and recharge action;
3) when voltage on filter capacitor reaches or close to when stablizing, utilize a phase-veversal switch dielectric amplifier, amplify the difference of the voltage on filter capacitor and reference voltage Vref;
4) utilize a fast analog-todigital converter to obtain phase-veversal switch dielectric amplifier output voltage values simultaneously;
5) change of fast analog-todigital converter Result is analyzed, obtain the instantaneous relative variation of measured capacitance.
CN201010118932.8A 2010-03-08 2010-03-08 Self-capacitance change measuring circuit with quick response CN102193033B (en)

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CN103207711B (en) * 2012-01-13 2015-01-07 深圳市汇春科技有限公司 Self-capacitance touch detection circuit and method
CN103308773A (en) * 2012-03-07 2013-09-18 上海海栎创微电子有限公司 Mutual capacitance variation measuring circuit with high precision and low power consumption
CN102830882B (en) * 2012-09-04 2015-05-13 北京集创北方科技有限公司 Touch detection circuit of capacitive touch screen
CN104049822B (en) * 2014-06-18 2017-02-15 深圳贝特莱电子科技股份有限公司 Detection system of touch screen control circuit
CN104158535B (en) * 2014-07-23 2017-06-16 三星半导体(中国)研究开发有限公司 FV convertor
CN104808063B (en) * 2015-04-23 2017-07-04 天津大学 A kind of impedance measuring circuit of triangle wave excitation
CN104807481B (en) * 2015-04-23 2017-06-13 天津大学 A kind of impedance based sensor measuring circuit of triangle wave excitation
CN104765507B (en) 2015-05-08 2018-06-05 上海天马微电子有限公司 A kind of filter circuit and touch control display apparatus
CN105652099B (en) * 2016-02-22 2018-10-12 西安电子科技大学 A kind of micro- capacitance difference detection method based on switching circuit

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Address after: 201203 Room 411, 4th Floor, Main Building (1 Building) of Zhangjiang Guochuang Center, 899 Dangui Road, Pudong New Area, Shanghai

Patentee after: Shanghai Hailichuang Microelectronic Co., Ltd.

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