JP2006234456A - Detection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect the shape of the surface of an object precisely. <P>SOLUTION: A detection device detects the shape of the surface of an object according to the potential of a connection point N between an electrode 51 for detection that opposes the object and forms a capacitor 50 for detection and a reference capacitor having capacitance CR. When the capacitance of the capacitor 50 for detection when the projection of the object opposes the electrode 51 for detection is set to C<SB>XR</SB>and the capacitance of the capacitor 50 for detection when the projection of the object opposes the electrode 51 for detection is set to C<SB>XV</SB>, the capacitance C<SB>R</SB>of the reference capacitor is selected so that C<SB>R</SB>>(C<SB>XR</SB>×C<SB>XV</SB>)<SP>1/2</SP>is met. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a technique for detecting the shape of a surface having fine irregularities such as human fingerprints and animal noseprints.

The capacitance of a capacitive element (hereinafter referred to as “detection capacitance”) composed of one electrode (hereinafter referred to as “detection electrode”) and an object adjacent thereto (hereinafter referred to as “target object”) is for detection. It varies depending on the distance between the electrode and the surface of the object. Techniques for detecting the surface shape of an object by detecting this capacitance have been proposed in the field of so-called fingerprint sensors. For example, in Patent Document 1, as shown in FIG. 8, a detection element 81 whose surface is covered with a dielectric has a capacitance element (hereinafter referred to as “reference capacitance element”) 82 having a specific capacitance. A technique for specifying the shape of the surface of an object by connecting in series and detecting the potential V at the connection point Q is disclosed. This patent document 1 also discloses a configuration including a transistor (hereinafter referred to as “reset transistor”) 85 for resetting the connection point Q to a predetermined potential (hereinafter referred to as “reset potential”) Vres. The reset transistor 85 is an active element that is interposed between the potential supply line 86 to which the reset potential Vres is applied and the connection point Q and switches between conduction and non-conduction between the two. According to this configuration, it is possible to eliminate unnecessary charges by setting the potential at the connection point Q to the reset potential Vres prior to the detection of the object, so that the detection accuracy can be improved.
Japanese Patent Laid-Open No. 2002-287887 (FIG. 1)

  However, in the configuration shown in FIG. 8, there is a problem that there is a limit to improving the accuracy of detecting the shape of the surface of the target object because, for example, capacitance is parasitic on each part such as the connection point Q. In particular, in the configuration in which the reset transistor 85 is connected to the connection point Q as shown in FIG. 8, the capacitance of the reset transistor 85 can be a cause of reducing the detection accuracy. The present invention has been made in view of such circumstances, and an object of the present invention is to solve the problem of detecting the shape of the surface of an object with high accuracy even when capacitance is parasitic in each part.

を満たすことにある。この構成によれば、検出用電極と基準容量素子との接続点に寄生する容量を何ら考慮することなく静電容量Ｃ_Rを選定した場合（すなわち上式を満たさない場合）と比較して、対象物の凸部が検出用電極と対向するときの接続点の電位（Ｖ_BR）と凹部が対向するときの接続点の電位（Ｖ_BV）との差分値（ΔＶ_B）を増大させることができるから、対象物の凸部と凹部とを明確に分別することが可能となる。 In order to solve this problem, a first feature of the detection device according to the present invention is that a detection electrode facing an object in contact with a detection surface, and a reference capacitive element in which one electrode is connected to the detection electrode And a device for detecting the shape of the surface of the target object according to the potential of the connection point between the detection electrode and the reference capacitor when the target object contacts the detection surface. When the convex portion of the target object is opposite to the detection electrode, the capacitance of the detection capacitor constituted by the detection electrode and the target object is C _XR, and the concave portion of the target object in contact with the detection surface is detected When the capacitance of the detection capacitor constituted by the detection electrode and the object when facing the electrode for detection is C _XV , the capacitance C _R of the reference capacitance element is

It is to satisfy. According to this configuration, as compared with the case where the capacitance _CR is selected without considering any capacitance parasitic at the connection point between the detection electrode and the reference capacitance element (that is, when the above equation is not satisfied), Increasing the difference value (ΔV _B ) between the potential (V _BR ) at the connection point when the convex portion of the object faces the detection electrode and the potential (V _BV ) at the connection point when the concave portion faces. Therefore, it is possible to clearly separate the convex portion and the concave portion of the object.

を満たすように選定される。この態様によれば、対象物の凸部が検出用電極と対向するときの接続点の電位（Ｖ_BR）と凹部が対向するときの接続点の電位（Ｖ_BV）との差分値（ΔＶ_B）をさらに増大させることができる。 If the capacitance parasitic to the wiring conducted to the connection point is C _S , more preferably, the capacitance C _R of the reference capacitance element is:

It is selected to satisfy. According to this aspect, the difference value (ΔV _B ) between the potential (V _BR ) at the connection point when the convex portion of the object faces the detection electrode and the potential (V _BV ) at the connection point when the concave portion faces. ) Can be further increased.

を満たすように選定される。この態様によれば、検出用電極と基準容量素子との接続点に寄生する静電容量やリセット用トランジスタの容量が存在する場合であっても、対象物の凸部が検出用電極と対向するときの接続点の電位（Ｖ_BR）と凹部が対向するときの接続点の電位（Ｖ_BV）との差分値（ΔＶ_B）を最大値とすることができる。 In the detection apparatus according to the present invention, a first terminal connected to a connection point between the detection electrode and the reference capacitive element, a second terminal connected to a potential supply line to which a reset potential V _A is applied, A reset transistor that switches between conduction and non-conduction in accordance with the potential of the control terminal is provided, and a reset operation for turning the reset transistor into a conduction state (on state), and the reset transistor in a non-conduction state (off state) A configuration in which the reading operation is executed is also adopted. In this configuration, the first potential that is one of the power supply potential Vdd and the ground potential (for example, if the reset transistor is an n-channel type, the power supply potential Vdd is the first potential and the reset transistor is a p-channel type). The ground potential is set to the first potential) and the second terminal, which is the other of the power supply potential Vdd and the ground potential, is applied to the first terminal and the second terminal. The capacitance of the reset transistor in the state is C _SW, and the capacitance between the control terminal and the first terminal during the reset operation is b · C _SW (where 0 ≦ b ≦ 1 ), The capacitance between the control terminal and the first terminal during the reading operation when the concave portion of the object in contact with the detection surface faces the detection electrode is represented by B _V · C _{S Where W} is the capacitance C _R of the reference capacitance element,

It is selected to satisfy. According to this aspect, even when there is a parasitic capacitance at the connection point between the detection electrode and the reference capacitance element or a reset transistor capacitance, the convex portion of the object faces the detection electrode. The difference value (ΔV _B ) between the potential at the connection point (V _BR ) at that time and the potential at the connection point (V _BV ) when the recesses face each other can be made the maximum value.

としたときの数値よりも大きくなるように、基準容量素子の静電容量Ｃ_Rが決定されていることにある。この構成によっても、第１の特徴に係る構成と同様に、接続点に寄生する容量を何ら考慮することなく静電容量Ｃ_Rを選定した場合（すなわち上式を満たさない場合）と比較して、差分値ΔＶ_Bを増大させることができる。 Further, a second feature of the detection apparatus according to the present invention includes a detection electrode facing the object in contact with the detection surface, and a reference capacitance element in which one electrode is connected to the detection electrode. A device for detecting the shape of the surface of an object according to the potential of the connection point between the detection electrode and the reference capacitor when the object contacts the detection surface, and the convex portion of the object in contact with the detection surface C _XR is the capacitance of the detection capacitor constituted by the detection electrode and the object in the first state where the detection electrode is opposed to the detection electrode, and the concave portion of the object in contact with the detection surface is the detection electrode. When the capacitance of the detection capacitor constituted by the detection electrode and the object in the second state facing each other is C _XV , the potential V _BR of the connection point in the first state and the second state The difference value ΔV _{B from} the potential V _{BV at the} connection point in FIG. Capacitance C _R ,

To be larger than the value when the electrostatic capacitance C _R of the reference capacitance element is to have been determined. Even in this configuration, as in the configuration according to the first feature, compared with the case where the capacitance _CR is selected without considering the capacitance parasitic to the connection point (that is, when the above equation is not satisfied). The difference value ΔV _B can be increased.

としたときの数値以上となるように、基準容量素子の静電容量Ｃ_Rが決定される。この態様によれば、差分値ΔＶ_Bをさらに増大させて検出の精度を向上させることができる。 In a more desirable mode, when the capacitance parasitic to the wiring conducted to the connection point is C _S , the difference value ΔV _B is the capacitance C _R of the reference capacitance element.

The capacitance C _R of the reference capacitive element is determined so as to be greater than or equal to According to this aspect, the detection accuracy can be improved by further increasing the difference value ΔV _B.

<A: Configuration of detection device>
FIG. 1 is a block diagram showing a configuration of a detection apparatus according to an embodiment of the present invention. This detection device D is a device for detecting the shape of the surface of an object in contact with a flat surface exposed to the outside (hereinafter referred to as “detection surface”). As shown in FIG. It has a sensor array unit 10 in contact with an object, a row selection circuit 20 and a column selection circuit 30 for operating the sensor array unit 10, and a detection circuit 40 for processing a signal detected by this operation.

  The sensor array unit 10 includes m row lines 11 (11 [1] to 11 [m]) that extend in the X direction (row direction) and are connected to the row selection circuit 20, and Y that is orthogonal to the X direction. The n column lines 13 (13 [1] to 13 [n]) extending in the direction (column direction) and connected to the column selection circuit 30 are paired with each column line 13 in the Y direction. It has n output lines 15 (15 [1] to 15 [n]) extending and connected to the detection circuit 40 (m and n are both natural numbers). A unit circuit U is arranged at the intersection of each row line 11 and each column line 13. Accordingly, these unit circuits U are arranged in a matrix of m rows × n columns across the X and Y directions. Each unit circuit U is a circuit for generating a signal (hereinafter referred to as “detection signal”) corresponding to the shape of the surface of the object facing the unit circuit U.

  FIG. 2 is a circuit diagram showing a configuration of each unit circuit U. In the drawing, only four unit circuits U in the (j−1) th column and the jth column belonging to the i-th row and the (i + 1) -th row are shown (i is 1 ≦ 1). (i is an integer satisfying i ≦ m, and j is an integer satisfying 1 ≦ j ≦ n), and the other unit circuits U have the same configuration. The configuration will be described below with particular attention paid to the unit circuit U in the i-th row and the j-th column. FIG. 2 illustrates a configuration in which all transistors included in the unit circuit U are n-channel type. However, part or all of the conductivity types of these transistors are appropriately changed to a p-channel type.

The detection electrode 51 shown in the figure is a conductive film body arranged in parallel with the detection surface, and its surface is covered with a dielectric (not shown). The detection electrode 51 is opposed to the surface of the object in contact with the detection surface with a dielectric (not shown) interposed therebetween. Therefore, the detection capacitor 50 is configured by the detection electrode 51, the object, and the dielectric sandwiched between the two. The capacitance C _X of the detection capacitor 50 varies according to the distance between the detection electrode 51 and the surface of the object. On the other hand, the reference capacitance element 52 is a capacitance in which the first electrode 521 connected to the detection electrode 51 at the connection point N and the second electrode 522 connected to the column line 13 [j] are opposed to each other. The potential at the connection point N is a potential obtained by dividing the potential difference between the object and the column line 13 [j] according to the electrostatic capacitance C _R of the reference capacitive element 52 and the electrostatic capacitance C _X of the detection capacitor 50. .

  A gate electrode of the amplifying transistor 53 is connected to the connection point N. The amplifying transistor 53 is a switching element for amplifying fluctuations in the potential at the connection point N to generate a detection signal (that is, converting the potential at the connection point N into a detection signal), and its source electrode has a power supply It is connected to a power supply line 61 to which a lower potential (hereinafter referred to as “ground potential”) Gnd is supplied. The power supply line 61 is commonly connected to all the unit circuits U and supplies the ground potential Gnd to each of the unit circuits U. On the other hand, the drain electrode of the amplifying transistor 53 is connected to the source electrode of the column selection transistor 54. The column selection transistor 54 is a switching element having a gate electrode connected to the column line 13 [j] and a drain electrode connected to the source electrode of the row selection transistor 55. The gate electrode of the row selection transistor 55 is connected to the i-th row line 11 [i], and the drain electrode is connected to the j-th column output line 15 [j].

Further, the drain electrode of the resetting transistor 57 is connected to the connection point N. The reset transistor 57 is a switching element for setting the potential at the connection point N to a predetermined potential (hereinafter referred to as “reset potential”) V _A. The source electrode of the reset transistor 57 is connected to a potential supply line 62 to which a reset potential V _A is supplied. The potential supply line 62 is a wiring that is commonly connected to all the unit circuits U and supplies the reset potential V _A to each of the unit circuits U. The gate electrode of the reset transistor 57 in the unit circuit U in the j-th column is connected to the column line 13 [j-1] in the (j−1) -th column adjacent to the preceding stage.

  The row selection circuit 20 shown in FIG. 1 sequentially selects each of the m row lines 11 [1] to 11 [m] for each predetermined period (hereinafter referred to as “row selection period”). This is a circuit (for example, a shift register) for applying a higher potential (hereinafter referred to as “power supply potential”) Vdd to the row line 11 [i] and applying the ground potential Gnd to the other row lines 11. When the power supply potential Vdd is applied to the row line 11 [i] by the row selection circuit 20, the row selection transistors 55 of the n unit circuits U belonging to the i-th row are simultaneously turned on. On the other hand, as shown in FIG. 3, the column selection circuit 30 has n column lines 13 [1] to 13 [n] for every predetermined period (hereinafter referred to as “column selection period”) within one row selection period. Are sequentially selected, and the power supply potential Vdd is applied to the selected column line 13 [j] and the ground potential Gnd is applied to the other column lines 13 (for example, a shift register).

Next, the operation of the detection device D will be described with particular attention paid to the unit circuit U in the j-th column belonging to the i-th row. The detection device D operates to reset the potential at the connection point N to the reset potential V _A (hereinafter referred to as “reset operation”) and to output a detection signal corresponding to the potential at the connection point N (hereinafter referred to as “read operation”). And execute. FIG. 4 is a circuit diagram showing the potential and capacitance of each part of the unit circuit U performing the reset operation. FIG. 5 is a circuit diagram showing the potential and electrostatic capacity of each part of the unit circuit U performing the read operation. It is a circuit diagram which shows a capacity | capacitance.

(1) Reset operation
As shown in FIGS. 3 and 4, when the column selection circuit 30 supplies the power supply potential Vdd to the column line 13 [j-1] at the timing T1 within the row selection period in which the row line 11 [i] is selected. The column selection transistors 54 of the unit circuits U belonging to the (j−1) th column are turned on, and the reset transistors 57 of the m unit circuits U belonging to the jth column are simultaneously turned on. . Therefore, the potential at the connection point N of each unit circuit U belonging to the j-th column is the reset potential V _A. When the timing T2, which is the end point of the (j-1) th column selection period, arrives, the column selection transistor 54 of each unit circuit U belonging to the (j-1) th column transitions to the OFF state, and The reset transistors 57 of the unit circuits U belonging to the j column are all turned off. Since the reset transistor 57 is turned on by supplying the power supply potential Vdd to the gate electrode as described above, the reset potential V _A is set to a potential equal to or lower than “Vdd−Vth” (Vth is the reset transistor 57). Threshold voltage).

(2) Read operation
As shown in FIGS. 3 and 5, the column selection circuit 30 starts applying the power supply potential Vdd to the column line 13 [j] at the timing T3 that is the start point of the j-th column selection period. Since the second electrode 522 of the reference capacitive element 52 is connected to the column line 13 [j] and the surface of the object is at the ground potential Gnd, when the power supply potential Vdd is supplied to the column line 13 [j], the column line A potential Vdd is applied to both ends of the detection capacitor 50 and the reference capacitor element 52 connected in series between 13 [j] and the object. At this time, the connection point N adds the potential obtained by dividing the potential Vdd and the reset potential V _A according to the relative ratio between the capacitance C _X of the detection capacitor 50 and the capacitance C _R of the reference capacitance element 52. At the potential. Since the electrostatic capacitance _CR is determined according to the distance between the detection capacitor 50 and the surface of the object, the potential at the connection point N is set to the distance between the detection capacitor 50 and the surface of the object during the reading operation. A corresponding potential V _B is obtained. When the power supply potential Vdd is supplied to the column line 13 [j], the reset transistor 57 of each unit circuit U in the (j + 1) th column is turned on, and each unit circuit U in the jth column is turned on. The column selection transistors 54 are simultaneously turned on. At this time, the row selection transistor 55 is in the ON state only in the unit circuit U in the i-th row. Therefore, in this column selection period, the connection point is connected to the j-th unit circuit U belonging to the i-th row. A detection signal corresponding to the N potential V _B (that is, a detection signal corresponding to the distance between the detection electrode 51 and the surface of the object) is output to the output line 15 [j].

  For the other unit circuits U, the above reset operation and the reading operation immediately after that are sequentially repeated, so that the detection electrode 51 of each unit circuit U for each of the unit circuits U of vertical m rows × horizontal n columns. And a detection signal corresponding to the distance from the surface of the object are sequentially input to the detection circuit 40. The detection circuit 40 generates data indicating the shape of the surface of the object based on the detection signals sequentially input from the output lines 15. By analyzing this data, the shape of the surface of the object is specified. As described above, in the present embodiment, unnecessary charges at the connection point N can be eliminated by performing a reset operation prior to detection of the detection signal corresponding to the potential at the connection point N. The detection accuracy can be improved as compared with a configuration in which the reset operation is not executed.

By the way, as described above, when the reset transistor 57 is turned on, the reset potential V _A is supplied to the connection point N. However, due to the capacitance associated with the reset transistor 57, the potential at the connection point N may fluctuate lower than the reset potential V _{A at} the timing T2 when the reset operation ends. That is, since the gate electrode and the drain electrode of the reset transistor 57 are capacitively coupled, when the potential applied to the gate electrode changes from the power supply potential Vdd to the ground potential Gnd at the timing T2, the potential of the drain electrode also decreases. As a result, the potential at the connection point N becomes lower than the reset potential V _A. The fluctuation of the potential at the connection point N can be a cause of hindering improvement in detection accuracy by the detection device D. Even if the capacitance of the reset transistor 57 does not become a problem, there is a possibility that the same problem may be caused by capacitances parasitic on various wirings connected to the connection point N. Therefore, in the present embodiment, the capacitance C _R of the reference capacitance element 52 is selected in consideration of the capacitance of the reset transistor 57 and the influence of the parasitic capacitance at the connection point N. The details of the selection method are as follows.

<B: Selection of capacitance C _R >
Now, when the ground potential Gnd is applied to the source electrode and the drain electrode of the reset transistor 57 and the power supply potential Vdd is applied to the gate electrode, the gate electrode, the source electrode, and the drain of the reset transistor 57 are turned on. If the capacitance _CSW is attached to the electrode, the capacitance of the gate-drain capacitance 731 in the reset operation shown in FIG. 4 (that is, the potential Vdd is applied to the gate electrode g and the drain electrode and The capacitance when the reset potential V _A is applied to the source electrode is expressed as “b · C _SW ” (where 0 ≦ b ≦ 1). Further, as shown in FIG. 4, a capacitance 71 having a capacitance C _S is parasitic at the connection point N. At this time, the charge amount Q _A stored at the connection point N is expressed by the following equation (1).

On the other hand, as shown in FIG. 5, the capacitance of the capacitor 731 existing between the gate and the drain of the reset transistor 57 in the read operation is set to “B · C _SW ” (0 ≦ B ≦ 1). Since the forward bias is applied to the reset transistor 57 during the reset operation and the reverse bias is applied during the read operation, the coefficient b is generally larger than the coefficient B. More specifically, the coefficient b is a coefficient. About 10 times B. Here, as shown in FIG. 5, when the potential at the connection point N during the read operation is “V _B ”, the charge amount Q _{B at} the connection point N at this time is expressed by the following equation (2).

In the reset operation and the read operation, neither the outflow of the charge from the connection point N nor the inflow of the charge to the connection point N occurs. Therefore, the charge amount Q _A in the equation (1) and the charge amount Q _{B in the} equation (2). Are equal (Q _A = Q _B ). Therefore, the following equation (3) representing the potential V _B at the connection point N during the read operation is derived from the equations (1) and (2).

なお、式（４）における「Ｂ_R・Ｃ_SW」は、リセット用トランジスタ５７のドレイン電極に電位Ｖ_BRが印加されるとともにそのゲート電極に電源電位Ｖddが印加されたときにゲート・ドレイン間に形成される容量７３１の静電容量である。同様に、式（５）における「Ｂ_V・Ｃ_SW」は、リセット用トランジスタ５７のドレイン電極に電位Ｖ_BVが印加されるとともにそのゲート電極に電源電位Ｖddが印加されたときにゲート・ドレイン間に形成される容量７３１の静電容量である。係数Ｂ_Rおよび係数Ｂ_Vは式（１）における係数ｂよりも小さい。例えば、係数ｂは、係数Ｂ_Rおよび係数Ｂ_Vの各々の１０倍程度の数値とされる。なお、式（４）および式（５）に示されるように読出動作においては対象物の凸部および凹部の何れが検出用電極５１に対向しているかによって接続点Ｎの電位は相違するが、リセット動作においてリセット用トランジスタ５７のドレイン電極はリセット電位Ｖ_Aに維持されるから、対象物の凸面および凹面の何れが検出用電極５１に対向しているかに拘わらず、リセット用トランジスタ５７の容量７３１の静電容量は一定値（ｂ・Ｃ_SW）となる。 By the way, the surface of an object such as a human finger has fine convex portions and concave portions. The capacitance C _X of the detection capacitor 50 differs depending on whether the convex portion or the concave portion on the surface of the object faces the detection electrode 51. Therefore, the capacitance of the detection capacitor 50 (that is, the maximum value of the capacitance C _X ) when the convex portion faces the detection electrode 51 during the reading operation is set to “C _XR ”. Assuming that the capacitance of the detection capacitor 50 (ie, the minimum value of the capacitance C _X ) when the recesses are opposed to each other is “C _XV ”, the expression (3) is convex to the detection electrode 51 during the reading operation. Equation (4) representing the potential V _BR of the connection point N when the portion is opposed, and Equation (5) representing the potential V _BV of the connection point N when the concave portion is opposed to the detection electrode 51, Can be rewritten.

Incidentally, "B _{R-C SW"} in the equation (4) is between the gate and drain when the power source potential Vdd is applied to its gate electrode the potential V _BR is applied to the drain electrode of the reset transistor 57 This is the capacitance of the capacitor 731 to be formed. Similarly, “B _V · C _SW ” in the equation (5) is the gate-drain connection when the potential V _BV is applied to the drain electrode of the reset transistor 57 and the power source potential Vdd is applied to the gate electrode. This is the capacitance of the capacitor 731 formed. Coefficient B _R and the coefficient B _V is smaller than the coefficient b in equation (1). For example, the coefficient b is a coefficient B _R and the coefficient B _V each 10 times the value of. As shown in the equations (4) and (5), in the reading operation, the potential at the connection point N differs depending on which of the convex portion and concave portion of the object faces the detection electrode 51. Since the drain electrode of the reset transistor 57 is maintained at the reset potential V _A in the reset operation, the capacitance 731 of the reset transistor 57 regardless of whether the convex surface or the concave surface of the object is opposed to the detection electrode 51. Has a constant value (b · C _SW ).

In order to improve the sensitivity of detection by the detection device D, the potential V _BR of the connection point N when the convex portion of the object faces the detection electrode 51 and the potential V _BV of the connection point N when the concave portion _faces. It is desirable that the difference with is large. This is because the greater the difference, the clearer the distinction between the convex portion and the concave portion facing the detection electrode 51. Therefore, as shown in the following formula (6), a difference value ΔV _B between the potential V _BV and the potential V _BR is considered.

Here, since so that the air layer is interposed in a gap between the detection electrode 51 and the surface when the recessed portion of the object is opposite to the detection electrode 51, the electrostatic capacitance C _XV of this time, the subject It is sufficiently smaller than the capacitance C _XR when the convex portion of the object faces the detection electrode 51 (C _XR >> C _XV ). Further, the capacitance C _XR is sufficiently larger than the parasitic capacitance C _S and the capacitance C _SW of the reset transistor 57 (C _XR >> C _S , C _XR >> C _SW ). Considering these circumstances, the equation (6) is approximated to the following equation (7).

この式（８）から明らかなように、寄生容量Ｃ_Sやリセット用トランジスタ５７の容量Ｃ_SWが大きいほど差分値ΔＶ_Bは小さくなる（すなわち検出の感度は低下する）。そこで、本実施形態においては、式（７）によって表わされる差分値ΔＶ_Bがより大きい数値となるように、基準容量素子５２の静電容量Ｃ_Rが選定される。以下、静電容量Ｃ_Rと差分値ΔＶ_Bとの関係を示す図６（式（７）をプロットしたグラフ）を参照しながら、より好適な静電容量Ｃ_Rについて検討する。なお、以下では式（７）から導出される数式に基づいて好適な静電容量Ｃ_Rを検討するが、この式（７）の代わりに式（８）を使用してもよい。 Further, the capacitance C _XR is sufficiently larger than the capacitance C _R of the reference capacitance element 52 (C _XR >> C _R ), and the capacitance C _XV is the capacitance C of the reference capacitance element 52. _When the form of the detection electrode 51 and the form of the dielectric covering the detection electrode 51 are selected so as to be sufficiently smaller than _R (C _XV << C _R ), Expression (7) approximates the following Expression (8). Is done.

As is apparent from the equation (8), the larger the parasitic capacitance C _S and the capacitance C _SW of the resetting transistor 57, the smaller the difference value ΔV _B (that is, the detection sensitivity decreases). Therefore, in the present embodiment, the capacitance C _R of the reference capacitance element 52 is selected so that the difference value ΔV _B represented by the equation (7) becomes a larger value. Hereinafter, a more suitable capacitance C _R will be examined with reference to FIG. 6 (a graph obtained by plotting Equation (7)) showing the relationship between the capacitance C _R and the difference value ΔV _B. Although considering the suitable capacitance C _R on the basis of a formula derived from equation (7) below, may be using equation (8) instead of the equation (7).

First, the capacitance C _R that maximizes the difference value ΔV _B is expressed by the following equation (9) from the content of the equation (7) (see FIG. 6).

Now, if the parasitic capacitance C _{S at} the connection point N and the capacitance C _SW of the reset transistor 57 are not taken into consideration, the capacitance C _{R at} this time (hereinafter referred to as “capacitance value C _R0 ” in particular). Is expressed by the following equation (10) by setting “C _S = 0” and “C _SW = 0” in equation (9).

Therefore, by setting the capacitance C _R of the reference capacitance element 52 to a number greater than the capacitance value C _R0 of formula (10), the parasitic capacitance C _S and the capacitance C the electrostatic capacitance _{without SW} of any consideration C _R Compared to the case where the capacitance C _R is smaller than the capacitance value C _R0 , the decrease in the difference value ΔV _B caused by these capacitances can be mitigated.

Meanwhile, in order to potential corresponding to the potential V _B at the connection point N at the time of reading operation of the distance between the detecting electrode 51 and the object, the electrostatic capacitance C _R of the reference capacitor element 52, convex object It is necessary to make the capacitance smaller than the capacitance C _XR of the detection capacitor 50 when the part contacts. Therefore, the electrostatic capacitance C _R of the reference capacitive element 52 in the present embodiment is a numerical value within the range R _c0 that is larger than the capacitance value C _R0 represented by the equation (10) and smaller than the capacitance C _XR. It is set (C _R0 <C _R <C _XR ). In other words, the difference value ΔV _B is larger than the numerical value ΔV ₀ calculated from the equation (7) when the capacitance C _R of the reference capacitive element 52 is set to the capacitance value C _R0 (that is, the difference value). The electrostatic capacitance C _R of the reference capacitive element 52 in the present embodiment is selected so that ΔV _B is a value within the range R _{v0 of} FIG.

Next, if only the parasitic capacitance C _{S at} the connection point N is considered and the capacitance C _SW of the resetting transistor 57 is not taken into consideration, the capacitance C _{R at} this time (hereinafter referred to as “capacitance value C _{R1 in} particular”). Is expressed by the following equation (11) by setting “C _SW = 0” in equation (9).

If the capacitance C _R of the reference capacitance element 52 is set to a value equal to or _larger than the capacitance value C _R1 of the equation (11), the capacitance C _R is selected without taking the parasitic capacitance C _S into consideration (ie, static). Compared with the case where the capacitance C _R is smaller than the capacitance value C _R1 ), the decrease in the difference value ΔV _B caused by this parasitic capacitance can be mitigated. Therefore, in a more desirable aspect, the capacitance C _R of the reference capacitance element 52 is a numerical value within the range R _c1 that is equal to or larger than the capacitance value C _R1 represented by the equation (11) and smaller than the capacitance C _XR. (C _R1 ≦ C _R <C _XR ). In other words, the difference value ΔV _B is equal to or greater than the numerical value ΔV ₁ calculated from the equation (7) when the capacitance C _R of the reference capacitive element 52 is set to the capacitance value C _R1 (that is, the difference value ΔV _The capacitance C _R of the reference capacitive element 52 is selected so that _B is a value within the range R _{v1 of} FIG.

Further, since the convex portion and the concave portion of the object can be clearly distinguished as the difference value ΔV _B is larger, more desirably, the electrostatic capacitance of the reference capacitor element 52 is set so that the difference value ΔV _B becomes the maximum value. The capacity C _R is set to a numerical value represented by the equation (9) (hereinafter referred to as “capacitance value C _R2 ”). For example, as shown in FIG. 6, the capacitance C _R of the reference capacitance element 52 is set to a numerical value within a range Rc ₂ that is equal to or larger than the capacitance value C _R2 and smaller than the capacitance C _XR ( C _R2 ≦ C _R <C _XR ).

Next, specific modes of each part of the unit circuit U according to this embodiment will be exemplified. In this embodiment, the power supply potential Vdd is 3.3 V, and the reset potential V _A is the ground potential. The gate insulating layers of the amplifying transistor 53 and the resetting transistor 57 are thin films having a thickness of about 4.5 μm formed of SiO ₂ (relative permittivity is 3.9). If the gate length of the amplifying transistor 53 is 3 μm and the gate width is 5 μm, the capacity of the amplifying transistor 53 is 12.9 fF. Here, in consideration of the capacitance of the amplifying transistor 53, the parasitic capacitance C _S at the connection point N is set to 13 fF. On the other hand, if the gate length of the reset transistor 57 is 3 μm and the gate width is 3 μm, the capacitance C _SW of the reset transistor 57 is 7.77 fF. The capacitance C _XR of the detection capacitor 50 when the convex portion of the object faces the detection electrode 51 is 400 fF, and the capacitance C _XV when the concave portion faces is 4 fF. Further, since the drain electrode and the source electrode of the reset transistor 57 are at the same potential during the reset period, the coefficient b can be considered to be about 0.5.

Next, FIG. 7 is a graph showing the relationship between the potential applied to the gate electrode of the resetting transistor 57 and its capacitance. As shown in the figure, for example, the capacitance (about 2.25 fF) of the reset transistor 57 when a reverse bias is applied as in the read operation is the same as when the forward bias is applied as in the reset operation. This is about 9% to 10% of the capacitance (about 25 fF) of the reset transistor 57. Further, since the capacitance between the gate-drain capacitance 731 and the gate-source capacitance 732 is substantially equal, the coefficient B _V is 0.045 to 0.05. However, the coefficient B _V is 0.045 below.

Substituting the above numerical values into equation (10), the capacitance value C _R0 when the parasitic capacitance 71 and the capacitance 731 of the reset transistor 57 are not taken into consideration is calculated to be about 40 fF. Further, the difference value ΔV _{B at} this time is about 1.89 V from the equation (7). If the actual capacitance C _R of the reference capacitance element 52 is set to a value larger than the capacitance value C _R0 , the concave portion is opposed to the potential V _{BR at} the connection point N when the convex portion faces the detection electrode 51. Since the potential V _BV and the difference value ΔV _B can be larger than 1.89 V, the shape of the surface of the object can be specified with high accuracy. For example, the capacitance value C _R1 calculated by substituting the above numerical values into the equation (11) is about 82 fF, and the difference value ΔV _{B at} this time is calculated to be about 2.15 V from the equation (7). Therefore, for example, if the capacitance C _R of the reference capacitance element 52 is set to a value equal to or larger than the capacitance value C _R1 , the convex portion and the concave portion of the object can be clearly determined. Further, when the above numerical value is substituted into the equation (9), the capacitance value C _R2 is calculated as 96 fF, and the difference value ΔV _{B at} this time is 2.16V. That is, if the capacitance C _R of the capacitance element is set to be equal to the capacitance value C _R2 , it is possible to more clearly discriminate the convex portion and the concave portion of the object.

<C: Modification>
Various modifications can be made to the embodiment described above. An example of a specific modification is as follows. In addition, you may combine each following aspect suitably.

(1) Modification 1
The reset transistor 57 may be a p-channel transistor. In this case, the ground potential Gnd is applied to the gate electrode of the reset transistor 57 during the reset operation, and the power supply potential Vdd is applied during the read operation. In the formulas (1) to (11) described in the embodiment, “Vdd” is changed to “−Vdd” and “V _A ” is changed to “−V _A ”. The optimum electrostatic capacitance C _R derived is the same as that in the embodiment (for example, the equation (9)).

(2) Modification 2
In the embodiment, the configuration in which the potential of the connection point N is reset to the reset potential V _A by the reset transistor 57 is illustrated, but the reset transistor 57 is not necessarily a necessary element. That is, for example, if the charge at the connection point N immediately before the read operation is so small that the detection accuracy is not affected, the configuration in which the reset transistor 57 and the potential supply line 62 are omitted (the configuration in which the reset operation is not executed) is also possible. Good. Also in this configuration, as in the embodiment, the electrostatic capacitance C _R of the reference capacitive element 52 is set to a value larger than the capacitance value C _R0 in FIG. 6, and more preferably a value greater than the capacitance value C _{R1 in} FIG. It is said. In other words, the electrostatic capacitance C _R of the reference capacitive element 52 is set so that the difference value ΔV _B is larger than the numerical value ΔV ₀ , and more preferably set to be equal to or larger than the difference value ΔV ₁ .

(3) Modification 3
The embodiment exemplifies a configuration in which the behavior of the reset transistor 57 of the unit circuit U located in the jth column is controlled according to the potential of the column line 13 in the previous column ((j−1) th column). However, the configuration for controlling the reset transistor 57 is not limited to this. For example, the gate electrode of the reset transistor 57 of the unit circuit U located in the j-th column is connected to the column line 13 of the next column (the (j + 1) -th column), and reset according to the potential of the column line 13 The transistor 57 may be controlled. A configuration in which the column line 13 is also used for controlling the reset transistor 57 is not necessarily required, and the reset transistor 57 may be controlled by an element separate from the column line 13. For example, a configuration in which a wiring arranged for each column of the unit circuit U is connected to the gate electrode of the resetting transistor 57 and the resetting transistor 57 is controlled according to the potential of this wiring is also adopted. As described above, the reset transistor 57 is a switching element that switches between conduction and non-conduction between the connection point N between the detection electrode 51 and the reference capacitance element 52 and the potential supply line 62 to which the reset potential V _A is applied. It does not matter whether the configuration for controlling the operation is sufficient.

(4) Modification 4
In the embodiment, a configuration in which a plurality of unit circuits U are arranged in a matrix is illustrated, but a configuration in which these unit circuits are arranged in a straight line may be used. Further, the configuration of each unit circuit U is not limited to the configuration of FIG. For example, in the embodiment, the configuration in which the second electrode 522 of the reference capacitive element 52 is connected to the column line 13 is illustrated, but the second electrode 522 may be connected to another part to which a constant potential is applied. Good. Further, the column line 13 and the column selection transistor 54 may be omitted. In this configuration, when the power supply potential Vdd is applied to the row line 11 [i], the row selection transistors 55 of the n unit circuits U belonging to the i-th row are turned on. Detection signals are output simultaneously to each of the output lines 15 [1] to 15 [n].

It is a block diagram which shows the structure of the detection apparatus which concerns on embodiment of this invention. It is a circuit diagram which shows the structure of each unit circuit. It is a timing chart which shows the waveform of the potential applied to each column line. It is a circuit diagram which shows the electric potential and electrostatic capacitance of each part in the unit circuit at the time of reset operation. It is a circuit diagram which shows the electric potential and electrostatic capacitance of each part in the unit circuit at the time of read-out operation. It is a graph which shows the relationship between the electrostatic capacitance C _R of the reference capacitance element and the difference value ΔV _B. It is a graph which shows the relationship between the capacity | capacitance of a transistor for reset, and gate potential. It is a circuit diagram for demonstrating the principle which detects the shape of the surface of a target object.

Explanation of symbols

D ... detection device, U ... unit circuit, 10 ... sensor array section, 20 ... row selection circuit, 30 ... column selection circuit, 40 ... detection circuit, 11 ... row line, 13 ... column line , 15... Output line, 50... Detection capacitor, 51... Detection electrode, 52 .. reference capacitance element, 53... Amplification transistor, 54. ... Reset transistor, 61 ... Power supply line, 62 ... Potential supply line.

Claims (6)

The detection electrode when the detection object is opposed to an object in contact with the detection surface, and a reference capacitive element having one electrode connected to the detection electrode, and the object is in contact with the detection surface And a device for detecting the shape of the surface of the object according to the potential of the connection point between the reference capacitance element and
When the convex portion of the object in contact with the detection surface is opposed to the detection electrode, the capacitance of the detection capacitor constituted by the detection electrode and the object is C _XR , When the capacitance of the detection capacitor formed by the detection electrode and the target object is C _XV when the concave portion of the target object that is in contact with the detection electrode is static, The capacitance _CR is

The detection apparatus characterized by satisfy | filling. When the capacitance parasitic to the wiring that conducts to the connection point is C _S , the capacitance C _R of the reference capacitance element is:

The detection device according to claim 1, wherein: Conduction and non-conduction between the first terminal connected to the connection point between the detection electrode and the reference capacitive element and the second terminal connected to the potential supply line to which the reset potential V _A is applied is the control terminal. A detection device that includes a reset transistor that switches according to a potential, and that performs a reset operation that turns on the reset transistor and a read operation that turns off the reset transistor;
A first potential that is one of a power supply potential Vdd and a ground potential is applied to the control terminal, and a second potential that is the other of the power supply potential Vdd and the ground potential is applied to the first terminal and the second terminal. The capacitance of the resetting transistor that has become conductive due to is set to C _SW, and the capacitance between the control terminal and the first terminal during the reset operation is set to b · C _SW (where 0 ≦ b ≦ 1), the capacitance between the control terminal and the first terminal during the reading operation when the concave portion of the object in contact with the detection surface faces the detection electrode is represented by B _V · C _SW When the electrostatic capacity C _R of the reference capacitive element is

The detection device according to claim 2, wherein: Detection device according to claim 3 the capacitance C _R of the reference capacitor element from claim 1, characterized in that less than the electrostatic capacitance C _XR. The detection electrode when the detection object is opposed to an object in contact with the detection surface, and a reference capacitive element having one electrode connected to the detection electrode, and the object is in contact with the detection surface And a device for detecting the shape of the surface of the object according to the potential of the connection point between the reference capacitance element and
In the first state in which the convex portion of the object in contact with the detection surface opposes the detection electrode, the capacitance of the detection capacitor constituted by the detection electrode and the object is C _XR , When the capacitance of the detection capacitor constituted by the detection electrode and the target object is C _XV in the second state in which the concave portion of the target object contacting the detection surface faces the detection electrode,
Difference [Delta] V _B and the potential V _BV of the connecting point in the second state the potential V _BR at the node in the first state, the capacitance C _R of the reference capacitive element,

And then to be larger than the number of time the detection device, characterized in that the capacitance C _R of the reference capacitor element is determined. When the capacitance parasitic to the wiring conducted to the connection point is C _S , the difference value ΔV _B is the capacitance C _R of the reference capacitance element.

The detection device according to claim 5, wherein a capacitance C _R of the reference capacitance element is determined so as to be equal to or greater than a numerical value of the reference capacitance element.

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