CN102207802B - Capacitance detection circuit - Google Patents

Abstract

The invention provides a capacitance detection circuit. The capacitance detection circuit comprises an analogue capacitance detection circuit, a pulse width modulation signal conversion digital circuit and a self-correcting counter, wherein the analogue capacitance detection circuit detects the touch capacitance of a panel according to a charging current and converts a detected capacitance value into a pulse width modulation control signal; the pulse width modulation signal conversion digital circuit converts the pulse width modulation control signal into a measurement count value according to a frequency signal; and the self-correcting counter adjusts the charging current or the frequency signal according to a difference between a range of the measurement count value and a predetermined detection range and further adjusts the predetermined detection range to make the predetermined detection range accordant with the range of the measurement count value. The capacitance detection circuit can improve the accuracy of a touch panel.

Description

A kind of capacitance detection circuit

Technical field

The present invention is relevant to a kind of capacitance detection circuit, espespecially a kind ofly is applied on the touch panel and the capacitance detection circuit of tool self-recision reconnaissance range function.

Background technology

Liquid crystal display (liquid crystal display, LCD) has compact advantage, replace gradually bulky cathode-ray tube (CRT) (cathode ray tube, the CRT) display of tradition, and be widely used in all types of electronic products.Along with the microminiaturization of the size of electronic product, hold such as traditional input medias such as keyboard or mouses without enough spaces on the product, so the touch panel (touch panel) of combination of touch control input and Presentation Function is at present the most popular input technology.Touch panel is of a great variety, mainly be divided into resistance-type, condenser type, ultrasonic formula and infrared sensing formula etc., wherein the operation principles of capacitive touch control techniques is when contacting with contact panel with human body or pointer, utilizes a capacitance detection circuit to come capacitance variations that sensing produces because of electrostatical binding to obtain touch position.

The capacitance detection circuit normal operation artificial capacitor circuit for detecting of prior art is detected the sense capacitance C of panel _SENSE, recycle a counter and obtain corresponding digital signal.Sense capacitance C _SENSEThe stray capacitance C that comprises panel itself _PANELAnd the touching capacitor C that causes because of touch action _FINGEROwing to the volume of panel is generally understood along with resolution increases its stray capacitance C _PANELAlso can become large, when finger touches arrives panel, the touching capacitor C that increases _FINGERVariation is with respect to the stray capacitance C of full wafer panel _PANEL, will become quite insignificant, also be C _PANEL＞＞C _FINGERAnd the capacitance variations that other assorted signal causes in the operating environment is also often much larger than the touching capacitor C _FINGERVariation, so capacitance detection circuit of prior art and can't effectively promote the accuracy of electric capacity detecting.On the other hand, in order to increase the touch-control accuracy, generally the input range value of electric capacity can be designed in the optimum linear district of capacitance detection circuit.Yet the factors such as humidity, temperature, external environment condition, processing procedure or component ageing all may change the input range value of electric capacity, if surpass the non-linear partial that the optimum linear district of capacitance detection circuit can enter circuit, so that resolution lowers greatly.

Summary of the invention

The object of the present invention is to provide a kind of capacitance detection circuit, if be intended to solve the non-linear partial that the optimum linear district that surpasses capacitance detection circuit that exists in the prior art then can enter circuit, so that the problem that resolution lowers greatly.

The present invention is achieved in that a kind of capacitance detection circuit, and described capacitance detection circuit comprises:

One artificial capacitor circuit for detecting, its foundation one charging current is detected the sense capacitance of a panel, and converts the capacitance that detects to a Wave-wide regulation controlled electric control signal;

One Wave-wide regulation controlled electric revolution word circuit, it is converted to a measuration meter numerical value according to a frequency signal with described Wave-wide regulation controlled electric control signal; And

One self-recision counter, it adjusts described charging current or described frequency signal according to the scope of described measuration meter numerical value and the difference between the predetermined reconnaissance range, and then adjusts described predetermined reconnaissance range so that it meets the scope of described measuration meter numerical value.

In the present invention, the present invention can adjust and upgrades the electric capacity reconnaissance range according to the change of electric capacity input value, allows the electric capacity reconnaissance range maintain in the optimum linear interval of circuit, the accuracy that therefore can improve touch panel.

Description of drawings

The synoptic diagram of the capacitance detection circuit that Fig. 1 a and Fig. 1 b provide for the embodiment of the invention.

Fig. 2 is the synoptic diagram of artificial capacitor circuit for detecting in the embodiment of the invention.

Fig. 3 a and Fig. 3 b are the synoptic diagram of Wave-wide regulation controlled electric revolution word circuit in the embodiment of the invention.

Fig. 4 a and Fig. 4 b are the synoptic diagram when Wave-wide regulation controlled electric revolution word circuit operates in the embodiment of the invention.

Fig. 5 a and Fig. 5 b are the synoptic diagram of self-recision counter in the embodiment of the invention.

Fig. 6 a～Fig. 6 c is the synoptic diagram when the self-recision counter operates in the embodiment of the invention.

Fig. 7 is the synoptic diagram of digital control current source in the embodiment of the invention.

Embodiment

In order to make purpose of the present invention, technical scheme and beneficial effect clearer, below in conjunction with drawings and Examples, the present invention is further elaborated.Should be appreciated that specific embodiment described herein only in order to explain the present invention, is not intended to limit the present invention.

Please refer to Fig. 1 a and Fig. 1 b, Fig. 1 a for first embodiment of the invention provide in the synoptic diagram of a capacitance detection circuit 10a, and the synoptic diagram of the capacitance detection circuit 10b that Fig. 1 b provides for second embodiment of the invention.Capacitance detection circuit 10a comprises an artificial capacitor circuit for detecting 200, a Wave-wide regulation controlled electric (pulse width modulation, PWM) revolution word circuit 300a, and a self-recision counter (self-calibration counter) 500a; Capacitance detection circuit 10b comprises an artificial capacitor circuit for detecting 200, a Wave-wide regulation controlled electric revolution word circuit 300b, and a self-recision counter 500b. Capacitance detection circuit 10a and 10b all utilize artificial capacitor circuit for detecting 200 to detect the sense capacitance C of a panel 20 _SENSE, and convert the capacitance that detects to a Wave-wide regulation controlled electric control signal PWM.As previously mentioned, sense capacitance C _SENSEThe stray capacitance C that comprises panel 20 itself _PANELAnd the touching capacitor C that causes because of touch action _FINGERThe Wave-wide regulation controlled electric control signal PWM that Wave-wide regulation controlled electric revolution word circuit 300a and 300b all can transmit artificial capacitor circuit for detecting 200 is converted to a digital measurement count value N _SENSE, its structure and running will have a detailed description in the instructions subsequent content.

In the capacitance detection circuit 10a of first embodiment of the invention, self-recision counter 500a comprises an input range corrector 400 and a digital control current source 700.According to the measuration meter numerical value of N _SENSEValue, input range corrector 400 exportable digital signal D corresponding to touch action _NTo late-class circuit (a for example digital signal processor).Simultaneously, capacitance detection circuit 10a also can store and judge the electric capacity reconnaissance range, and produces according to this charging current I that a corresponding scope conversion ratio K exports to adjust digital control current source 700 _M, and then adjust the wide time span of whole ripple so that optimized electric capacity reconnaissance range to be provided.

In the capacitance detection circuit 10b of second embodiment of the invention, self-recision counter 500b comprises an input range corrector 400 and a digital control oscillator (digital controloscillator) 800.According to the measuration meter numerical value of N _SENSEValue, input range corrector 400 exportable digital signal D corresponding to touch action _NTo late-class circuit (a for example digital signal processor).Simultaneously, capacitance detection circuit 10b also can store and judge the electric capacity reconnaissance range, and adjusts according to this frequency signal CK of digital control oscillator 800 outputs, and then adjusts whole sampling frequency so that optimized electric capacity reconnaissance range to be provided.

Please refer to Fig. 2, Fig. 2 is the synoptic diagram of artificial capacitor circuit for detecting 200 in the embodiment of the invention.Artificial capacitor circuit for detecting 200 comprises switch QN1～QN3 and a comparator C MP.Switch QN1 operates according to the Wave-wide regulation controlled electric control signal PWM that comparator C MP produces, and switch QN2 and QN3 operate according to frequency signal SG2 and SG3 respectively, wherein the responsibility cycle of Wave-wide regulation controlled electric control signal PWM (duty cycle) is decided by a detecting voltage VRAMP, and frequency signal SG2 and SG3 tool opposite phase.Switch QN1～QN3 can be metal-oxide-semiconductor (MOS) (metal-oxide-semiconductor, MOS) transistor switch, or the element of other tool similar functions, and the embodiment of Fig. 2 explains with nmos transistor switch.According to the Wave-wide regulation controlled electric control signal PWM that its control end receives, switch QN1 optionally receives charging current I with its first end _MBe sent to its second end.The first end of switch QN2 is coupled to the second end of switch QN1, and the second end is coupled to panel 20, can control charging current I according to the frequency signal SG2 that its control end receives _MThe charge path of counter plate 20.The first end of switch QN3 is coupled to panel 20, the second ends and is coupled to a negative bias VSS, can come according to the frequency signal SG3 that its control end receives the discharge path of control panel 20.Comparator C MP receives a reference voltage V at its first input end _REF, its second input end is coupled to the second end of switch QN1, and its output terminal is coupled to the control end of switch QN1.

Charging current I _MCan be provided by digital control current source 700, its value is capable of regulating, capacitance detection circuit 10a as shown in Figure 1a; Perhaps, charging current I _MCan be provided by certain power supply, its value is for fixing the capacitance detection circuit 10b shown in Fig. 1 b.When Wave-wide regulation controlled electric control signal PWM and frequency signal SG2 tool noble potential, charging current I _MCan come counter plate 20 chargings, detecting voltage V by switch QN1 and the QN2 of conducting _RAMPAccurate position also promote thereupon.As detecting voltage V _RAMPValue surpass a reference voltage V _REFThe time, the Wave-wide regulation controlled electric control signal PWM of comparator C MP output can switch to electronegative potential by noble potential, and then closing switch QN1.Then, frequency signal SG3 can switch to noble potential, and the capacitor memory energy of panel 20 can be discharged to negative bias VSS by the switch QN3 of conducting.If with T _ONRepresent the time (also being the ON time of switch QN1) of Wave-wide regulation controlled electric control signal PWM tool noble potential within a cycle, the charging process of panel 20 can be represented by following formula:

I _M*T _ON＝C _SENSE*V _REF＝(C _FINGER+C _PANEL)*V _REF

Also be T _ON=(C _FINGER+ C _PANEL)/I _M(1)

Please refer to Fig. 3 a and Fig. 3 b, Fig. 3 a is the synoptic diagram of Wave-wide regulation controlled electric revolution word circuit 300a in the first embodiment of the invention, and Fig. 3 b is the synoptic diagram of Wave-wide regulation controlled electric revolution word circuit 300b in the second embodiment of the invention.The Wave-wide regulation controlled electric revolution word circuit 300a of the first embodiment comprises a phasing unit 310 and a totalizer 320.Phasing unit 310 can produce tool certain trigger starting point and a frequency f _CLKFrequency signal CK.Totalizer 320 can receive the Wave-wide regulation controlled electric control signal PWM that artificial capacitor circuit for detecting 200 transmits, and when being triggered by frequency signal CK the value of detecting Wave-wide regulation controlled electric control signal PWM, if Wave-wide regulation controlled electric control signal PWM tool noble potential, totalizer can be with the measuration meter numerical value of N of output _SENSEAdd 1.The Wave-wide regulation controlled electric revolution word circuit 300b of the second embodiment comprises a totalizer 320.Totalizer 320 can receive the frequency signal CK that Wave-wide regulation controlled electric control signal PWM that artificial capacitor circuit for detecting 200 transmits and self-recision counter 500b transmit, and when being triggered by frequency signal CK the value of detecting Wave-wide regulation controlled electric control signal PWM, if Wave-wide regulation controlled electric control signal PWM tool noble potential, totalizer can be with the measuration meter numerical value of N of output _SENSEAdd 1.

Please refer to Fig. 4 a and Fig. 4 b, Fig. 4 a is the synoptic diagram when Wave-wide regulation controlled electric revolution word circuit 300a operates in the first embodiment of the invention, and Fig. 4 b is the synoptic diagram when Wave-wide regulation controlled electric revolution word circuit 300b operates in the second embodiment of the invention.Fig. 4 a and Fig. 4 b have shown detecting voltage V _RAMP, Wave-wide regulation controlled electric control signal PWM and frequency signal CK waveform, and measuration meter numerical value of N _SENSEValue.Because panel 20 itself has stray capacitance C unavoidablely _PANELEven when touching not occuring, the Wave-wide regulation controlled electric control signal PWM of artificial capacitor circuit for detecting 200 outputs can correspond to a basic count value N _BASELINEWhen touching occured, the Wave-wide regulation controlled electric control signal PWM of artificial capacitor circuit for detecting 200 outputs can correspond to a measuration meter numerical value of N _SENSEBasic count value N _BASELINEWith the measuration meter numerical value of N _SENSEAs follows:

$N_{\mathrm{BASELINE}}=\frac{f_{\mathrm{CLK}}\×C_{\mathrm{PANEL}}\×V_{\mathrm{REF}}}{I_M}---\left(2\right)$

$N_{\mathrm{SENSE}}=\frac{f_{\mathrm{CLK}}\×(C_{\mathrm{FINGER}}+C_{\mathrm{PANEL}})\×V_{\mathrm{REF}}}{I_M}---\left(3\right)$

Can obtain the actual count value Δ N of corresponding practical touch behavior according to formula (2) and formula (3), its value is as follows:

$\mathrm{\ΔN}=N_{\mathrm{SENSE}}-N_{\mathrm{BASELINE}}=\frac{f_{\mathrm{CLK}}{\×C}_{\mathrm{FINGER}}\×V_{\mathrm{REF}}}{I_M}---\left(4\right)$

Shown in formula (1), (T for example of the gate time when each, inherent switch QN1 opened in cycle _ON, T _ON1～T _ON3), its length is decided by the time length that whether the touching behavior occurs and the touching behavior occurs.Shown in formula (3), the measuration meter numerical value of N _SENSEWith charging current I _MBe inversely proportional to, and the trigger rate f of frequency signal CK _CLKBe directly proportional.The present invention adjusts electric capacity reconnaissance range (have and be described in more detail) according to actual count value Δ N in the instructions subsequent content, wherein the capacitance detection circuit 10a of the first embodiment adjusts charging current I by self-recision counter 500a _MValue to change gate time T _ON1～T _ON3(shown in Fig. 4 a), and then adjust the electric capacity reconnaissance range; The capacitance detection circuit 10b of the second embodiment adjusts frequency cycle of signal CK so that frequency f by self-recision counter 500b _CLK1～f _CLK3Differ from one another (shown in Fig. 4 b), and then adjust the electric capacity reconnaissance range.

Please refer to Fig. 5 a and Fig. 5 b, Fig. 5 a is the synoptic diagram of self-recision counter 500a in the first embodiment of the invention, and Fig. 5 b is the synoptic diagram of self-recision counter 500b in the second embodiment of the invention.The input range corrector 400 of self-recision counter 500a and 500b all comprises a subtracter 410, a comparer 420, a maximal value buffer 430, a minimum value buffer 440, a range adjustment circuit 450, and a counter 460.

The measuration meter numerical value of N that subtracter 410 can transmit Wave-wide regulation controlled electric revolution word circuit 300a or 300b _SENSEDeduct basic count value N _BASELINE, and then obtain corresponding to the actual count value Δ N of touch action.Maximal value buffer 430 and minimum value buffer 440 are interior maximum count value N among resulting all results when having respectively previous electric capacity detecting _MAXWith least count value N _MIN, maximum count value N _MAXWith least count value N _MINBetween be the predetermined reconnaissance range of present electric capacity.Comparer 420 can and before be stored in the maximum count value N of maximal value buffer 430 with present actual count value Δ N _MAXMake comparisons, and and before be stored in least count value N in the minimum value buffer 440 _MINMake comparisons; If the scope of actual count value Δ N is equivalent to predetermined reconnaissance range, this moment, range adjustment circuit 450 meetings come control figure control current source 700 or digital control oscillator 800 according to actual count value Δ N; If the scope of actual count value Δ N is greater than predetermined reconnaissance range, this moment, range modulator 450 meetings be multiplied by a scope conversion ratio K (K＜1) with actual count value Δ N, came control figure control current source 700 (to increase charging current I according to scope conversion ratio K again _MValue) or digital control oscillator 800 (frequency of reducing work frequency signal CK); If the scope of actual count value Δ N is less than predetermined reconnaissance range, this moment, range modulator 450 meetings be multiplied by a scope conversion ratio K (K＞1) with actual count value Δ N, came control figure control current source 700 (reducing the value of charging current IM) or digital control oscillator 800 (increasing the frequency of frequency signal CK) according to scope conversion ratio K again.On the other hand, the present invention can utilize counter 460 to set an adjustment cycle T _AdjIf, for example with adjustment cycle T _AdjBe made as 100, range modulator 450 just can be adjusted after whenever receiving 100 actual count value Δ N, so can avoid changing too continually the electric capacity reconnaissance range.

Please refer to Fig. 6 a～Fig. 6 c, Fig. 6 a～Fig. 6 c is the synoptic diagram during self-recision counter 500a and 500b running in the embodiment of the invention.In the embodiment shown in Fig. 6 a～Fig. 6 c, suppose maximum count value N _MAXWith least count value N _MINBe respectively 1023 and 0, T _TOUCHDuring the representative generation touching behavior.In the embodiment shown in Fig. 6 a, because actual count value Δ N is in preset range, range modulator 450 can be come control figure control current source 700 or digital control oscillator 800 according to present actual count value Δ N.In the embodiment shown in Fig. 6 b, the scope of supposing actual count value Δ N is 116～749, also namely in available reconnaissance range 0～115 and 750～1023 interval all can't utilize, this moment, range modulator 450 meetings be amplified to 0～1023 with the scope of former actual count value Δ N, and then optimized electric capacity reconnaissance range is provided.In the embodiment of Fig. 6 c, the scope of supposing actual count value Δ N is 0～1682, also be former reconnaissance range and can't comprise 1024～1682 interval, this moment, range modulator 450 can be contracted to the scope of former actual count value Δ N 0～1023 and then optimized electric capacity reconnaissance range is provided.

Please refer to Fig. 7, Fig. 7 is the synoptic diagram of digital control current source 700 in the embodiment of the invention.Digital control current source 700 comprises two transistor switch QPL and QPR, a capacitor C _IN, a reference current source I _M, and a matrix current adjustment circuit 750.Transistor switch QPL and QPR can be the element of PMOS transistor switch or other tool similar functions, and its On current is respectively by I _MAnd I _M' represent.

Matrix current adjustment circuit 750 comprises the current mirror that a plurality of transistor switch QP1～QPn form, and can distinguish the On current I of replica transistor switch QPL _MSo that the current value of different multiples to be provided, couple the addition electric current to capacitor C by interrupteur SW 1～SWn respectively again _INIn other words, electric current I _M' in one part of current provided by transistor switch QPR, other parts then are the On current I of transistor switch QP1～QPn replica transistor switch QPL _MThe rear current value that provides adds up.Transistor switch QP1～QPn can be the element of PMOS transistor switch or other tool similar functions.The running of interrupteur SW 1～SWn is controlled by range modulator 400, and the number of actuating switch SW1～SWn is more, electric current I _M' value larger: if the scope of actual count value Δ N less than preset range, the number that the present invention can reduce actuating switch SW1～SWn is to reduce charging current I _M' value, so the duration of charging of electric capacity can lengthen, and therefore can increase gate time to amplify the electric capacity reconnaissance range; If the scope of actual count value Δ N is greater than preset range, the present invention can increase the number of actuating switch SW1～SWn to improve charging current I _M' value, so the duration of charging of electric capacity can shorten, and therefore can reduce gate time to dwindle the electric capacity reconnaissance range.

In sum, if the input range value of electric capacity produces change because of factors such as humidity, temperature, external environment condition, processing procedure or component ageings, to such an extent as in the time of can't effectively using present electric capacity reconnaissance range, the present invention can adjust and upgrades the electric capacity reconnaissance range according to the change of electric capacity input value, allow the electric capacity reconnaissance range maintain in the optimum linear interval of circuit, the accuracy that therefore can improve touch panel.

The above only is preferred embodiment of the present invention, not in order to limiting the present invention, all any modifications of doing within the spirit and principles in the present invention, is equal to and replaces and improvement etc., all should be included within protection scope of the present invention.

Claims (10)

1. a capacitance detection circuit is characterized in that, described capacitance detection circuit comprises:

One artificial capacitor circuit for detecting, its foundation one charging current is detected the sense capacitance of a panel, and converts the capacitance that detects to a Wave-wide regulation controlled electric control signal;

One Wave-wide regulation controlled electric revolution word circuit, it is converted to a measuration meter numerical value according to a frequency signal with described Wave-wide regulation controlled electric control signal; And

One self-recision counter, it adjusts described charging current or described frequency signal according to the scope of described measuration meter numerical value and the difference between the predetermined reconnaissance range, and then adjusts described predetermined reconnaissance range so that it meets the scope of described measuration meter numerical value.

2. capacitance detection circuit as claimed in claim 1 is characterized in that, described artificial capacitor circuit for detecting comprises: one first switch, a second switch, one the 3rd switch and a comparer;

Described the first switch, it operates according to described Wave-wide regulation controlled electric control signal, and comprises:

One first end is used for receiving described charging current;

One second end; And

One control end is used for receiving described Wave-wide regulation controlled electric control signal;

Described second switch, it operates according to one first control signal, and comprises:

One first end is coupled to the second end of described the first switch;

One second end is coupled to described panel so that the detecting voltage corresponding to described sense capacitance to be provided; And

One control end is used for receiving described the first control signal;

Described the 3rd switch, it operates according to one second control signal, and comprises:

One first end is coupled to the second end of described second switch;

One second end is coupled to a negative bias; And

One control end is used for receiving described the second control signal, and described the first and second control signals are inverting each other; And

Described comparer is used for producing according to the difference of described detecting voltage and a reference voltage

Described Wave-wide regulation controlled electric control signal, described comparer comprises:

One first input end is used for receiving described reference voltage;

One second input end is coupled to the first end of described second switch; And

One output terminal is coupled to the control end of described the first switch, is used for exporting described Wave-wide regulation controlled electric control signal.

3. capacitance detection circuit as claimed in claim 1 is characterized in that, described self-recision counter comprises:

One input range corrector, it produces a scope conversion ratio according to the difference between described measuration meter numerical range and the described predetermined reconnaissance range; And

One digital control current source is used for producing described charging current is also adjusted described charging current according to described scope conversion ratio value.

4. capacitance detection circuit as claimed in claim 3 is characterized in that, described input range corrector comprises:

One subtracter is used for described measuration meter numerical value is deducted a basic count value corresponding to described panel stray capacitance, and then a corresponding actual count value is provided;

One maximal value buffer is used for storing the maximum count value corresponding to the described predetermined reconnaissance range upper limit;

One minimum value buffer is used for storing the least count value corresponding to described predetermined reconnaissance range lower limit;

One comparer is used for more described actual count value, described maximum count value and described least count value with the scope of judging described measuration meter numerical value and the difference between the described predetermined reconnaissance range; And

One range adjustment circuit, be used for when the scope of described measuration meter numerical value exceeds described predetermined reconnaissance range, by exporting described scope conversion ratio so that described digital control current source increases the value of described charging current, or in described measuration meter numerical range during less than described predetermined reconnaissance range, by exporting described scope conversion ratio so that described digital control current source reduces the value of described charging current.

5. capacitance detection circuit as claimed in claim 4 is characterized in that, described input range corrector also comprises:

One counter is used for controlling work period of described range adjustment circuit.

6. capacitance detection circuit as claimed in claim 3 is characterized in that, described Wave-wide regulation controlled electric revolution word circuit comprises:

One phasing unit is used for producing described frequency signal; And

One totalizer, be used for receiving the described frequency signal that described Wave-wide regulation controlled electric control signal that described artificial capacitor circuit for detecting transmits and described phasing unit transmit, when being triggered by described frequency signal, detect the value of described Wave-wide regulation controlled electric control signal, and when described Wave-wide regulation controlled electric control signal tool one specific potential, increase described measuration meter numerical value.

7. capacitance detection circuit as claimed in claim 1 is characterized in that, described Wave-wide regulation controlled electric revolution word circuit comprises:

One totalizer, be used for receiving the described frequency signal that described Wave-wide regulation controlled electric control signal that described artificial capacitor circuit for detecting transmits and described self-recision counter transmit, when being triggered by described frequency signal, detect the value of described Wave-wide regulation controlled electric control signal, and when described Wave-wide regulation controlled electric control signal tool one specific potential, increase described measuration meter numerical value.

8. capacitance detection circuit as claimed in claim 1 is characterized in that, described self-recision counter comprises:

One input range corrector, it produces a scope conversion ratio according to the difference between described measuration meter numerical range and the described predetermined reconnaissance range; And

One digital control oscillator, the frequency that it produces described frequency signal and adjust described frequency signal according to described scope conversion ratio.

9. capacitance detection circuit as claimed in claim 8 is characterized in that, described input range corrector comprises:

One subtracter is used for described measuration meter numerical value is deducted a basic count value corresponding to described panel stray capacitance, and then a corresponding actual count value is provided;

One maximal value buffer is used for storing the maximum count value corresponding to the described predetermined reconnaissance range upper limit;

One minimum value buffer is used for storing the least count value corresponding to described predetermined reconnaissance range lower limit;

One comparer is used for more described actual count value, described maximum count value and described least count value with the scope of judging described measuration meter numerical value and the difference between the described predetermined reconnaissance range; And

One range adjustment circuit, be used for when the scope of described measuration meter numerical value exceeds described predetermined reconnaissance range, by exporting described scope conversion ratio so that described digital control oscillator reduces the trigger rate of described frequency signal, or in described measuration meter numerical range during less than described predetermined reconnaissance range, by exporting described scope conversion ratio so that described digital control oscillator improves the trigger rate of described frequency signal.

10. capacitance detection circuit as claimed in claim 9 is characterized in that, described input range corrector also comprises:

One counter is used for controlling work period of described range adjustment circuit.

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