CN211785805U - Differential mutual capacitance detection circuit, chip and equipment - Google Patents
Differential mutual capacitance detection circuit, chip and equipment Download PDFInfo
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- CN211785805U CN211785805U CN201922229063.5U CN201922229063U CN211785805U CN 211785805 U CN211785805 U CN 211785805U CN 201922229063 U CN201922229063 U CN 201922229063U CN 211785805 U CN211785805 U CN 211785805U
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Abstract
The utility model discloses a differential mutual capacitance detection circuit, a chip and a device, relating to the mutual capacitance detection field, comprising an amplifier, a feedback capacitor, a first switch and at least two induction elements; at least two induction elements are connected in parallel and are respectively and independently connected with the inverting input end of the amplifier; one end of the feedback capacitor is connected with the inverting input end of the amplifier, and the other end of the feedback capacitor is connected with the output end of the amplifier to form a first feedback loop; one end of the first switch is connected with the inverting input end of the amplifier, and the other end of the first switch is connected with the output end of the amplifier to form a second feedback loop. The utility model discloses can detect inductive element's mutual capacitance value, improve inductive element's effective mutual capacitance value and account for the ratio.
Description
Technical Field
The utility model belongs to the technical field of mutual capacitance detection and specifically relates to a differential formula mutual capacitance detection circuitry, chip and equipment are related to.
Background
The mutual capacitance detection technology has a wide application range, such as detecting finger touch on a touch screen or sensing fingerprint lines in a fingerprint identification process. Fig. 1 is a schematic diagram of an inductive element array based on the mutual capacitance detection principle in the prior art, and since the induced electric field between the driving electrode TX and the sensing electrode RX in the inductive element 1 decreases as the conductors approach, the distance between the conductors can be known by detecting the variation of the mutual capacitance of the inductive element 1.
The mutual capacitance of the sensing element includes an intrinsic mutual capacitance and an effective mutual capacitance, wherein the mutual capacitance not affected by the conductor is the intrinsic mutual capacitance, and the mutual capacitance varying with the distance between the conductors is the effective mutual capacitance. The ratio of effective mutual capacitance values of the sensing elements is increased, the amplification factor of the output signal quantity of the detection circuit can be increased, and the requirement on the signal dynamic range of a subsequent analog-to-digital converter is reduced. Since the effective mutual capacitance of the sensing element is variable, the ratio of the effective mutual capacitance of the sensing element is increased, and how to reduce the intrinsic mutual capacitance of the sensing element needs to be considered.
In the prior art, a basic capacitor is mainly arranged in a detection circuit, and an intrinsic mutual capacitance value of an induction element is offset through the basic capacitance value, so that the ratio of an effective mutual capacitance value of the induction element is improved. However, the base capacitor in the detection circuit occupies an additional chip area, which increases the chip cost. In addition, the basic capacitor is fixed on the detection circuit, and an additional adjusting circuit is needed to be arranged for adjusting the basic capacitance value, so that the basic capacitance value is not easy to adjust, and the application range of the chip is limited.
SUMMERY OF THE UTILITY MODEL
The utility model discloses aim at solving one of the technical problem that exists among the prior art at least. Therefore, the utility model provides a differential mutual capacitance detection circuit can detect inductive element's mutual capacitance value, improves inductive element's effective mutual capacitance value's the ratio of occupying.
The utility model also provides a differential formula mutual capacitance detects chip.
The utility model also provides a differential formula mutual capacitance check out test set.
In a first aspect, an embodiment of the present invention provides a differential mutual capacitance detection circuit: the circuit comprises an amplifier, a feedback capacitor, a first switch and at least two induction elements;
at least two induction elements are connected in parallel and are respectively and independently connected with the inverting input end of the amplifier; one end of the feedback capacitor is connected with the inverting input end of the amplifier, and the other end of the feedback capacitor is connected with the output end of the amplifier to form a first feedback loop; one end of the first switch is connected with the inverting input end of the amplifier, and the other end of the first switch is connected with the output end of the amplifier to form a second feedback loop.
The utility model discloses differential formula mutual capacitance detection circuitry has following beneficial effect at least:
1. the mutual capacitance value of each sensing element can be detected;
2. the number of the induction elements is adjustable, and the expansion is easy;
3. the ratio of effective mutual capacitance of the sensing elements can be improved in a differential mode;
4. and a basic capacitor is not required to be additionally arranged, so that the structure of the detection circuit is simplified.
According to the utility model discloses a differential type mutual capacitance detection circuit of other embodiments still includes the second switch, and the second switch is established ties with feedback electric capacity to it is parallelly connected with first switch.
Through setting up the second switch, the utility model discloses a differential type mutual capacitance detection circuit can accumulate and calculate to can improve detection circuitry output signal's SNR.
In a second aspect, an embodiment of the present invention provides a differential mutual capacitance detection chip, including a differential mutual capacitance detection circuit.
The utility model discloses differential formula mutual capacitance detects chip has following beneficial effect at least:
1. the mutual capacitance value of the sensing elements can be detected;
2. the differential mutual capacitance detection circuit in the chip does not need to be provided with a basic capacitor, so that the area of the chip is reduced, and the cost of the chip is reduced.
In a third aspect, an embodiment of the present invention provides a differential mutual capacitance detection device, including a differential mutual capacitance detection chip.
The utility model discloses differential formula mutual capacitance check out test set has following beneficial effect at least:
1. the mutual capacitance value of the sensing elements can be detected;
2. the differential mutual capacitance detection chip in the equipment does not need to be internally provided with a basic capacitor, so that the equipment cost is reduced.
Drawings
FIG. 1 is a schematic diagram of a prior art sensor array based on mutual capacitance detection;
fig. 2 is a schematic diagram of an embodiment of a differential mutual capacitance detection circuit according to the present invention;
fig. 3 is a schematic diagram of another embodiment of a differential mutual capacitance detection circuit according to an embodiment of the present invention;
fig. 4 is a schematic diagram of another embodiment of a differential mutual capacitance detection circuit according to an embodiment of the present invention.
Detailed Description
The conception and the resulting technical effects of the present invention will be described clearly and completely with reference to the following embodiments, so that the objects, features and effects of the present invention can be fully understood. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all embodiments, and other embodiments obtained by those skilled in the art without inventive labor based on the embodiments of the present invention all belong to the protection scope of the present invention.
In the description of the present invention, if a feature is referred to as being "disposed", "fixed", "connected", or "mounted" on another feature, it can be directly disposed, fixed, or connected to the other feature or indirectly disposed, fixed, connected, or mounted to the other feature.
In the description of the embodiments of the present invention, if "a plurality" is referred to, it means two or more; if reference is made to "first" or "second", this should be understood to distinguish between features and not to indicate or imply relative importance or to implicitly indicate the number of indicated features or to implicitly indicate the precedence of the indicated features.
Referring to fig. 1, a schematic diagram of an array of sensing elements based on the mutual capacitance detection principle in the prior art is shown. As shown in fig. 1, the diamonds connected horizontally represent driving electrodes TX, the diamonds connected vertically represent sensing electrodes RX, and sensing elements 1 are formed where the driving electrodes TX and the sensing electrodes RX cross. The driving electrode TX and the sensing electrode RX constitute two poles of the sensing element 1, respectively. When a conductor approaches an inductive element, coupling between two electrodes near the conductor is affected, thereby changing the magnitude of the mutual capacitance of the inductive element between the two electrodes. Because the induced electric field between the driving electrode and the induction electrode in the induction element is weakened along with the approach of the conductor, the distance between the conductors can be known by detecting the variation of the mutual capacitance value of the induction element.
Example 1
Referring to fig. 2, a schematic diagram of a specific embodiment of a differential mutual capacitance detection circuit according to an embodiment of the present invention is shown. As shown in fig. 2, the first sensing element 10 and the second sensing element 11 are connected in parallel, and are respectively and independently connected to the inverting input terminal N of the amplifier; one end of the feedback capacitor C is connected with the inverting input end N of the amplifier, and the other end of the feedback capacitor C is connected with the output end V of the amplifierOForming a first feedback loop; one end of the first switch S1 is connected to the inverting input terminal N of the amplifier, and the other end of the first switch S1 is connected to the output terminal V of the amplifierOAnd forming a second feedback loop. Wherein, the mutual capacitance C of the first sensing element 10aIncluding an intrinsic mutual capacitance value CMaAnd an effective mutual capacitance value CTMaMutual capacitance C of the second inductive element 11bIncluding an intrinsic mutual capacitance value CMbAnd an effective mutual capacitance value CTMb。CTMLarger indicates that the conductor is closer to the inductive element. The driving electrode of the first inductive element 10 is TXa and the driving electrode of the second inductive element 11 is TXb.
Reset phase
Closing S1 applies a voltage VTX1 to TXa, a voltage VTX2 to TXb, and an operating voltage VCM to the non-inverting input P of the amplifier.
Inverting input terminal N and output terminal V of amplifierOIs reset, is VCM, the total charge of the detection circuit is:
Q1＝(VCM-VTX1)·(CMa-CTMa)+(VCM-VTX2)·(CMb-CTMb) (1)
charge transfer phase
S1 is turned off, a voltage VTX2 is applied to TXA, a voltage VTX1 is applied to TXB, the voltage at the inverting input N of the amplifier remains VCM due to the virtual short circuit characteristic at the input of the amplifier, and the output V isOVoltage of VOUT, capacitance of feedback capacitor C is CFThe total charge amount of the detection circuit is:
according to conservation of charge, Q1＝Q2And calculating to obtain:
since the sensing elements have substantially the same structure and the process variation within a small range is very small, the intrinsic mutual capacitance values of the sensing elements with similar distances are very similar, the intrinsic mutual capacitance values of the first sensing element 10 and the second sensing element 11 cancel each other out, and equation (3) can be simplified as follows:
due to the mutual capacitance C of the first inductive element 10a＝CMa-CTMaMutual capacitance C of the second inductive element 11b＝CMb-CTMbThen, the mutual capacitance difference between the first sensing element 10 and the second sensing element 11 is:
measuring the mutual capacitance C of the first inductive element 10aAccording to measured CaAnd Δ C calculated from the formula (5)abAnd calculating to obtain the mutual capacitance C of the second sensing element 11b。
In another embodiment of the differential mutual capacitance detection circuit of the embodiment of the present invention, based on embodiment 1, the normalized mutual capacitance value C of the first sensing element 10 is presetaX is any real number, and is calculated from the equation (5)abAnd calculating to obtain the normalized mutual capacitance C of the second sensing element 11b。
Example 2
Referring to fig. 3, a schematic diagram of another specific embodiment of a differential mutual capacitance detection circuit according to an embodiment of the present invention is shown. As shown in fig. 3, in embodiment 1, a third inductive element 12 is added, and the first inductive element 10, the second inductive element 11, and the third inductive element 12 are connected in parallel and are respectively and independently connected to the inverting input terminal N of the amplifier; one end of the feedback capacitor C is connected with the inverting input end N of the amplifier, and the other end of the feedback capacitor C is connected with the output end V of the amplifierOForming a first feedback loop; one end of the first switch S1 is connected to the inverting input terminal N of the amplifier, and the other end of the first switch S1 is connected to the output terminal V of the amplifierOAnd forming a second feedback loop. Wherein, the mutual capacitance C of the first sensing element 10aIncluding an intrinsic mutual capacitance value CMaAnd an effective mutual capacitance value CTMaMutual capacitance C of the second inductive element 11bIncluding an intrinsic mutual capacitance value CMbAnd an effective mutual capacitance value CTMbMutual capacitance C of the third inductive element 12cIncluding an intrinsic mutual capacitance value CMcAnd an effective mutual capacitance value CTMc. The driving electrode of the first sensing element 10 is TXa, the driving electrode of the second sensing element 11 is TXb, and the driving electrode of the third sensing element 12 is TXc.
First, the procedure of example 1 was followed, based on the measured CaAnd Δ C calculated from the formula (5)abThe mutual of the second inductive elements 11 is calculatedCapacitance value Cb. Then, the voltage input of TXA and TXB is disconnected, and the following steps are carried out:
reset phase
Closing S1, applying a voltage VTX2 to TXB and VTX3 to TXc, the operating voltage at the non-inverting input P of the amplifier remains VCM.
Inverting input terminal N and output terminal V of amplifierOIs reset, is VCM, the total charge of the detection circuit is:
Q1＝(VCM-VTX2)·(CMb-CTMb)+(VCM-VTX3)·(CMc-CTMc) (6)
charge transfer phase
S1 is turned off, a voltage VTX3 is applied to TXB, a voltage VTX2 is applied to TXc, the voltage at the inverting input N of the amplifier remains VCM due to the virtual short circuit characteristic at the input of the amplifier, and the output V isOThe voltage is VOUT, and the capacitance of the feedback capacitor is CFThe total charge amount of the detection circuit is:
according to conservation of charge, Q1＝Q2And calculating to obtain:
since the intrinsic mutual capacitance values of the sensing elements at close distances are very similar, the intrinsic mutual capacitance values of the second sensing element 11 and the third sensing element 12 cancel each other out, and equation (8) can be simplified as follows:
due to the mutual capacitance C of the second inductive element 11b＝CMb-CTMbMutual capacitance C of the third inductive element 12c＝CMc-CTMcThen, the mutual capacitance difference between the second sensing element 11 and the third sensing element 12 is:
obtaining the mutual capacitance C of the second inductive element 11 according to the calculationbAnd Δ C calculated from the formula (10)bcCalculating the mutual capacitance C of the third inductive element 12c。
In another embodiment of the differential mutual capacitance detection circuit of the embodiment of the present invention, based on embodiment 1, the normalized mutual capacitance value C of the first sensing element 10 is presetaIs 0, Δ C calculated from the formula (5)abAnd calculating to obtain the normalized mutual capacitance C of the second sensing element 11b. Normalized mutual capacitance value C according to the second inductive element 11bAnd Δ C calculated from the formula (10)bcAnd calculating to obtain the normalized mutual capacitance value C of the third sensing element 12c。
Example 3
In another embodiment of the differential mutual capacitance detection circuit of the embodiment of the present invention, based on embodiment 1, the input voltages of TXa and TXb have the same amplitude and phase.
Reset phase
At closure S1, the input voltages of TXa and TXb are both 0V, and the operating voltage of the non-inverting input P of the amplifier is still VCM.
Inverting input terminal N and output terminal V of amplifierOIs reset, is VCM, the total charge of the detection circuit is:
Q1＝VCM·(CMa-CTMa)+VCM·(CMb-CTMb) (11)
charge transfer phase
S1 is turned off, a voltage-VTX is applied to TXA and a voltage VTX is applied to TXB, the voltage at the inverting input N of the amplifier remains VCM due to the virtual short-circuit characteristic at the input of the amplifier, and the output V isOVoltage of VOUT, capacitance of feedback capacitor C is CFThe total charge amount of the detection circuit is:
according to conservation of charge, Q1＝Q2And calculating to obtain:
the intrinsic mutual capacitance values of the first sensing element 10 and the second sensing element 11 cancel each other, and equation (13) can be simplified as follows:
due to the mutual capacitance C of the first inductive element 10a＝CMa-CTMaMutual capacitance C of the second inductive element 11b＝CMb-CTMbThen, the mutual capacitance difference between the first sensing element 10 and the second sensing element 11 is:
measuring the mutual capacitance C of the first inductive element 10aAccording to measured CaAnd Δ C calculated from the formula (15)abAnd calculating to obtain the mutual capacitance C of the second sensing element 11b。
Example 4
Referring to fig. 4, a schematic diagram of another specific embodiment of a differential mutual capacitance detection circuit according to an embodiment of the present invention is shown. As shown in fig. 4, according to embodiment 1, a second switch S2 is added, the second switch S2 is connected in series with a feedback capacitor C, one end of the feedback capacitor C is connected to the inverting input terminal N of the amplifier, the other end of the feedback capacitor C is connected to one end of a second switch S2, and the other end of the second switch S2 is connected to the output terminal V of the amplifierOForming a first feedback loop; one end of the first switch S1 is connected to the inverting input terminal N of the amplifier, and the other end of the first switch S1 is connected to the output terminal V of the amplifierOAnd forming a second feedback loop. Wherein the first inductive elementMutual capacitance value C of 10aIncluding an intrinsic mutual capacitance value CMaAnd an effective mutual capacitance value CTMaMutual capacitance C of the second inductive element 11bIncluding an intrinsic mutual capacitance value CMbAnd an effective mutual capacitance value CTMb. The driving electrode of the first inductive element 10 is TXa and the driving electrode of the second inductive element 11 is TXb.
First reset phase
S1 and S2 are closed, applying a voltage VTX1 to TXa, a voltage VTX2 to TXb, and an operating voltage VCM to the non-inverting input P of the amplifier.
Inverting input terminal N and output terminal V of amplifierOIs reset, is VCM, the total charge of the detection circuit is:
Q1＝(VCM-VTX1)·(CMa-CTMa)+(VCM-VTX2)·(CMb-CTMb) (16)
a first charge transfer phase
With the opening S1 and S2 still closed, a voltage VTX2 is applied to TXa and a voltage VTX1 is applied to TXb, the voltage at the inverting input N of the amplifier remains VCM due to the virtual short at the input of the amplifier.
The charge amount of the first inductive element 10 changes to Δ QMa＝(VTX1-VTX2)·(CMa-CTMa) The charge amount of the second inductive element 11 is changed to Δ QMb＝(VTX2-VTX1)·(CMb-CTMb) The changed charge amount of the first and second sensing elements 10 and 11 is transferred to the feedback capacitor C, and the charge amount stored in the feedback capacitor C is QCF1＝-(ΔQMa+ΔQMb) Namely:
QCF1＝(VTX2-VTX1)·(CTMb-CTMa)+(VTX1-VTX2)·(CMb-CMa) (17)
second reset phase
Closing S1, opening S2, applying a voltage VTX1 to TXA and a voltage VTX2 to TXB, keeping the charge amount stored in the feedback capacitor C unchanged, and keeping the total charge amount of the detection circuit as follows:
Q3＝(VCM-VTX1)·(CMa-CTMa)+(VCM-VTX2)·(CMb-CTMb)+QCF1(18)
second charge transfer phase
Open S1, close S2, apply voltage VTX2 to TXa and voltage VTX1 to TXb.
The charge amount of the first inductive element 10 changes to Δ QMa＝(VTX1-VTX2)·(CMa-CTMa) The charge amount of the second inductive element 11 is changed to Δ QMb＝(VTX2-VTX1)·(CMb-CTMb) The changed charge amount of the first and second sensing elements 10 and 11 is transferred to the feedback capacitor C, and the charge amount Q stored in the feedback capacitor C isCF2＝QCF1-(ΔQMa+ΔQMb) Namely:
QCF2＝2·(VTX2-VTX1)·(CTMb-CTMa)+2·(VTX1-VTX2)·(CMb-CMa) (24)
repeating the steps of the second reset phase and the second charge transfer phase m times (m is a natural number), and obtaining the charge quantity stored by the feedback capacitor C:
in addition, according to the capacitance C of the feedback capacitor CFAnd the voltage value distributed on the feedback capacitor C, obtaining:
QCF(m+2)＝CF·(VCM-VOUT) (20)
from formulae (19) and (20), we obtain:
the intrinsic mutual capacitance values of the first sensing element 10 and the second sensing element 11 cancel each other, and equation (21) can be simplified as follows:
due to the mutual capacitance C of the first inductive element 10a＝CMa-CTMaOf 1 atMutual capacitance C of two inductive elements 11b＝CMb-CTMbThen, the mutual capacitance difference between the first sensing element 10 and the second sensing element 11 is:
as can be seen from equations (22) and (23), the amplifier output terminal V can be increased by performing m-times of summation calculation of the amount of charge stored in the feedback capacitor COThereby improving the signal-to-noise ratio of the output signal of the amplifier and reducing the accuracy requirement of the subsequent analog-to-digital converter.
The embodiments of the present invention have been described in detail with reference to the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made without departing from the spirit of the present invention within the knowledge of those skilled in the art. Furthermore, the embodiments of the present invention and features of the embodiments may be combined with each other without conflict.
Claims (4)
1. A differential mutual capacitance detection circuit is characterized by comprising an amplifier, a feedback capacitor, a first switch and at least two sensing elements;
at least two induction elements are connected in parallel and are respectively and independently connected with the inverting input end of the amplifier; one end of the feedback capacitor is connected with the inverting input end of the amplifier, and the other end of the feedback capacitor is connected with the output end of the amplifier to form a first feedback loop; one end of the first switch is connected with the inverting input end of the amplifier, and the other end of the first switch is connected with the output end of the amplifier to form a second feedback loop.
2. The differential mutual capacitance detection circuit of claim 1 further comprising a second switch in series with the feedback capacitance and in parallel with the first switch.
3. A differential mutual capacitance detection chip comprising the differential mutual capacitance detection circuit of claim 1 or 2.
4. A differential mutual capacitance sensing device comprising the differential mutual capacitance sensing chip of claim 3.
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| CN201922229063.5U CN211785805U (en) | 2019-12-12 | 2019-12-12 | Differential mutual capacitance detection circuit, chip and equipment |
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| CN201922229063.5U CN211785805U (en) | 2019-12-12 | 2019-12-12 | Differential mutual capacitance detection circuit, chip and equipment |
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