Patent Description:
A fingerprint pattern is different for every person and thus widely used in personal identification. In particular, a fingerprint is widely used in various fields, such as finance, criminal investigations, security, etc. as a means for personal authentication.

A fingerprint detecting sensor has been developed to identify an individual by detecting a fingerprint. The fingerprint detecting sensor is a device which contacts a finger of a person and recognizes a fingerprint of the finger, and used as a means for determining whether he/she is a legitimate user or not.

Recently, needs for personal authentication and security enhancement are rapidly increasing in mobile markets, and security-related businesses through mobile systems are being actively proceeding.

Reflecting this trend, studies for commercializing a semiconductor-type single-chip fingerprint sensor are actively conducted in many companies. However, in order to use a fingerprint detecting sensor chip in a mobile terminal, a high sensitive capacitive sensor circuit and other circuits which are insensitive to noise, are required for obtaining a reliable fingerprint image. Further, since a fingerprint detection chip is normally installed in a mobile apparatus, low power is a basic feature of the chip.

Various detecting methods, such as optical methods, thermal sensing methods, and capacitive methods, are known as a method of implementing a fingerprint detecting sensor.

Among them, the principle of a capacitive fingerprint sensor is that a fingerprint image is formed by converting a difference of capacitances formed between an uppermost metal plate and a ridge of a fingerprint and between the uppermost metal plate and a valley of the fingerprint into an electrical signal to compare a size of the electric signal with a size of a reference signal, and then digitalizing and imaging thereof.

As a method of processing a signal sensed by the uppermost metal plate, a charge sharing method, a feedback capacitive sensing method, a sample and hold method, a charge transfer method, etc. may be provided. Among them, the feedback capacitive sensing method has an advantage in that, since a circuit is simple, the size of a sensor electrode, i.e. the uppermost metal plate can be reduced while a high quality image is obtained. However, the fingerprint sensor using the feedback capacitive sensing method has a problem in that the best sensitivity is not provided in signal processing. The reason is that it is difficult to accurately detect a difference of response signals formed by a relationship between the uppermost metal plate and a ridge of a finger and a relationship between the uppermost metal plate and a valley of the finger, due to a thickness of a molding structure formed on the uppermost metal plate. That is, thickness variations of the molding structure disposed between the finger and the uppermost metal plate may limit the operating range of a reference voltage, and act as a decisive factor degrading the quality of the fingerprint image formed by the fingerprint detecting apparatus.

Accordingly, a technology of enabling a feedback capacitive sensing type fingerprint detecting apparatus to obtain an optimal sensitivity level and be insensitive to various changes in a surrounding environment.

<CIT> discloses a capacitance type fingerprint detector. There is a detection electrode that contacts the finger and is mounted above a driving and sensing electrodes, which sense a change in capacitive coupling between them.

<CIT>, <CIT> and <CIT> also disclose different fingerprint detectors.

An objective of the present invention is to solve problems of an existing technology described above.

Another objective of the present invention is to variably optimize a sensitivity level of a feedback capacitive sensing type fingerprint detecting apparatus depending on the circumstances.

Still another objective of the present invention is to suppress an influence of external noise on a fingerprint detecting apparatus.

The above and other objects, features, and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing in detail exemplary embodiments thereof with reference to the accompanying drawings, in which:.

Various embodiments will now be described more fully with reference to the accompanying drawings in which some embodiments are shown. However, since the invention is not limited to the embodiments disclosed hereinafter, the embodiments of the invention should be implemented in various forms. In the drawings, some additional components that have no relationship to explanation of example embodiments of the present invention may be omitted for clarity, and like numerals refer to like elements throughout the specification.

It will be understood that when an element is referred to as being "connected to" or "coupled to" another element, it may be directly connected or coupled to the other element or it may be indirectly connected or coupled to another element with an intervening element therebetween. It will be further understood that the terms "comprises," "comprising," "includes," and/or "including," when used herein, specify the presence of elements and/or components, but do not preclude the presence or addition of one or more elements and/or components unless stated otherwise.

<FIG> is a diagram showing a schematic configuration of a fingerprint detecting apparatus in accordance with an embodiment of the present invention.

Referring to <FIG>, a fingerprint detecting apparatus includes a sensor array <NUM> having a plurality of fingerprint sensor devices <NUM> which form a plurality of columns and rows. Each of the fingerprint sensor devices <NUM> is enabled by a horizontal scanner <NUM> and a vertical scanner <NUM> to output a signal related to detection of a fingerprint. The signal from the fingerprint sensor device <NUM> is output through a buffer <NUM>. One buffer <NUM> is arranged at every column of the fingerprint sensor devices <NUM>. That is, a signal from the fingerprint sensor device <NUM> disposed at one column is output through one buffer <NUM>.

<FIG> is a diagram for describing a configuration of the fingerprint sensor device <NUM> in <FIG> in accordance with a first embodiment of the present invention.

Referring to <FIG>, the fingerprint detecting apparatus includes the sensor array <NUM> and an external electrode (or a bezel, <NUM>). The external electrode <NUM> is isolated from the sensor array <NUM> and disposed therearound. The external electrode <NUM> functions to transmit a driving voltage Vdrv for detection of a fingerprint to a subject (a finger). That is, the driving voltage Vdrv is applied to the external electrode <NUM>, and the driving voltage Vdrv is supplied to a finger of a person through the external electrode <NUM>. Then, as a response thereto, a predetermined signal is output from each fingerprint sensor device <NUM> of the sensor array <NUM>.

Meanwhile, the sensor array <NUM> includes, as described above, the plurality of fingerprint sensor devices <NUM> that form columns and rows. The fingerprint sensor device <NUM> in accordance with the first embodiment of the present invention includes an electrode as a sensing electrode <NUM>. The sensing electrode <NUM> is selectively connected to a first input N1 of an amplifier A. A reference voltage Vref is supplied to a second input of the amplifier A. The first input N1 and the second input of the amplifier A may be an inverting input terminal and a non-inverting input terminal, respectively. A gain controller <NUM> is connected between the first input N1 and an output N2 of the amplifier A. The gain controller <NUM> is an element for varying a gain of the amplifier A, which will be described later in detail.

Meanwhile, an electrostatic discharge (ESD) protection circuit <NUM> may be further formed between the sensing electrode <NUM> and the first input N1 of the amplifier A.

The ESD protection circuit <NUM> is a circuit for preventing an electrostatic discharge, i.e. ESD generated between the sensing electrode <NUM> and the amplifier A, and includes a PMOS transistor PT and an NMOS transistor NT which are connected in series between a power voltage VDD and a ground potential. Each gate of the PMOS transistor PT and NMOS transistor NT is commonly connected to a source thereof.

When a bipolar electrostatic discharge higher than the power voltage VDD occurs between the sensing electrode <NUM> and the first input N1 of the amplifier A, the PMOS transistor PT is turned on and the NMOS transistor NT is turned off. At this time, the maximum potential of a node N3 disposed between the PMOS transistor PT and the NMOS transistor NT is limited to a value of the power voltage VDD plus a threshold voltage of the PMOS transistor PT.

Meanwhile, when a negative electrostatic discharge lower than the ground potential occurs between the sensing electrode <NUM> and the first input N1 of the amplifier A, the NMOS transistor NT is turned on and the PMOS transistor PT is turned off. At this time, the minimum potential of the node N3 between the PMOS transistor PT and the NMOS transistor NT is limited to a value of the ground potential minus a threshold voltage of the NMOS transistor NT.

Accordingly, even when a bipolar electrostatic discharge or a negative electrostatic discharge is input, the electrostatic discharge, i.e., ESD can be prevented since a voltage limited to a value below or above a certain level is transmitted.

Meanwhile, since the above described is only an example of a configuration of the ESD protection circuit <NUM>, the ESD protection circuit <NUM> can be implemented to another conventional configuration and disposed on a different position from the above described. The ESD protection circuit <NUM> may be omitted as well. Connection between the first input N1 of the amplifier A and the sensing electrode <NUM> turns on/off by a first switch S1, and a second switch S2 is connected between both ends of the gain controller <NUM>. In addition, a third switch S3 is connected to the output N2 of the amplifier A. The first switch S1 is a switch that serves for the fingerprint sensor device <NUM> to receive a signal from a finger according to a driving voltage Vdrv, the second switch S2 is a switch that resets data stored in the gain controller <NUM> of the amplifier A. In addition, the third switch S3 is a switch that selectively opens an output of the fingerprint sensor device <NUM>, that is, a switch that selectively controls an output signal of the fingerprint sensor device <NUM> to be transmitted to an external apparatus. Operations of the first to third switches S1 to S3 during detection of a fingerprint will be described later, in detail.

Hereinafter, a configuration of the fingerprint sensor device <NUM> of <FIG> will be described in detail with reference to <FIG> and <FIG>.

<FIG> and <FIG> are respectively a cross-sectional view and a perspective view showing a configuration of the fingerprint sensor device <NUM>. <FIG> only shows a configuration of conductive layers M1 to M4 and a shield layer SL in <FIG> for clarity of the drawing.

Referring to <FIG> and <FIG>, the fingerprint sensor device <NUM> is formed in a structure including a plurality of conductive layers M1 to M4 and a shield layer SL. The conductive layers M1 to M4 may be metal layers to which certain voltages are applied, and the shield layer SL is a metal layer to which a ground potential is applied. Insulating layers I2, I2, <NUM>, and I4 are formed between the conductive layers M1 to M4, and between the conductive layers M1 and M2 and the shield layer SL. The insulating layers I2, I2, <NUM>, and I4 may be formed of a conventional insulating material, such as SiO2, SiN, SiNOX, glass, etc..

A first conductive layer M1 is the uppermost layer to which a sensing electrode <NUM> is disposed.

The sensing electrode <NUM> is connected to the first input N1 of the amplifier A, and the connection is on/off by the first switch S1. A wire connecting the sensing electrode <NUM> and the first input N1 of the amplifier A passes through a shield electrode <NUM> of the shield layer SL, and a first feedback capacitance electrode <NUM> of a second conductive layer M2. For this purpose, via holes V1 and V2 may be formed on the shield electrode <NUM> and the first feedback capacitance electrode <NUM>.

Meanwhile, a shield electrode surrounding a periphery of the sensing electrode <NUM>, i.e. a guard ring G1 is formed in the first conductive layer M1. The guard ring G1 may be connected to the ground potential or another appropriate potential to minimize generation of a parasitic capacitance due to a relationship with an adjacent fingerprint sensor device <NUM>. A second guard ring (not shown) is formed to surround a periphery of the sensing electrode <NUM> and the first guard ring G1. In this case, the first guard ring G1 may be connected to the ground potential. Although the guard ring G1 is described to have a ring shape in this embodiment, but is not limited thereto. The guard ring G1 may be formed in various shapes, such as a circular shape, a non-circular shape, a polygonal shape, etc. and formed as a protection electrode to minimize interference from an adjacent metal.

A protection layer m protecting the sensing electrode <NUM> is formed on the uppermost conductive layer M1. The protection layer m protects the sensing electrode <NUM> from ESD and outer abrasion.

The sensing electrode <NUM> forms a capacitance in relation to a finger F in contact the sensing electrode <NUM>. The finger F is formed of ridges and valleys, and each sensing electrode <NUM> forms a different capacitance when it touches a ridge of the finger F from when it touches a valley of the finger F. When the sensing electrode <NUM> touches a ridge of the finger F, a capacitance Cm corresponding to a thickness of the molding layer m is formed between the sensing electrode <NUM> and the finger F. When the sensing electrode <NUM> touches a valley of the finger F, a capacitance Cm corresponding to a thickness of the molding layer m and a capacitance Cair corresponding to an air layer between the molding layer m and the valley of the finger F are formed between the sensing electrode <NUM> and the finger F. Like this, a capacitance formed between the sensing electrode <NUM> and the finger F is changed depending on which part of a fingerprint is in contact with the sensing electrode <NUM>, and an output signal Vout is changed depending on the capacitance. Accordingly, it is possible to find out features of the ridge and valley through the size of the output signal Vout.

The shield layer SL is formed under the first conductive layer M1 and have the shield electrode <NUM>. The shield electrode <NUM> is connected to the ground potential. As described later, a feedback capacitance of the amplifier A is formed by the gain controller <NUM> consisting of from the second conductive layer M2 to the fourth conductive layer M4, and parasitic capacitances Cp1 and Cp2 may exist between the sensing electrode <NUM> of the first conductive layer M1 and the first feedback capacitance electrode <NUM> of the second conductive layer M2. The first parasitic capacitance Cp1 is a parasitic capacitance formed by a relation between the sensing electrode <NUM> and the shield electrode <NUM>, and the second parasitic capacitance Cp2 is a parasitic capacitance formed by a relation between the shield electrode <NUM> and the first feedback capacitance electrode <NUM>.

First, the first parasitic capacitance Cp1 is described. Since the sensing electrode <NUM> is the closest electrode to the finger F, the first parasitic capacitance Cp1 may be much affected by accessibility to the finger F or other external noises. However, since the shield electrode <NUM> is connected to the ground potential, charges stored in the first parasitic capacitance Cp1 escape to the ground potential. That is, the effect of the first parasitic capacitance Cp1 during detection of a fingerprint is minimized due to the shield electrode <NUM>.

Next, the second parasitic capacitance Cp2 is described. The second parasitic capacitance Cp2 is formed between the shield electrode <NUM> and the first feedback capacitance electrode <NUM>. The shield electrode <NUM> is connected to the ground potential, and the first feedback capacitance electrode <NUM> is connected to the first input N1 of the amplifier A to have a potential of a reference voltage Vref in the ideal case. That is, since a potential difference (a voltage) between the shield electrode <NUM> and the first feedback capacitance electrode <NUM> remains constant, and each area of the shield electrode <NUM> and the first feedback capacitance electrode <NUM>, a distance between the shield electrode <NUM> and the first feedback capacitance electrode <NUM>, and a dielectric constant of the insulating layer I2 disposed between the shield electrode <NUM> and the first feedback capacitance electrode <NUM> are values known by design, the second parasitic capacitance Cp2 is a calculable value. The calculable second parasitic capacitance Cp2 can be easily removed using a separate parasitic capacitance removal circuit, or can be used as a value to be compensated during detection of a fingerprint. Further, through the calculation thereof, the amount of capacitance of the gain controller <NUM> to be explained later can be adjusted by compensating the calculated second parasitic capacitance Cp2.

In summary, a noise due to the first parasitic capacitance Cp1 among the parasitic capacitances between the first conductive layer M1 and the second conductive layer M2 is naturally removed by the shield electrode <NUM>, and a noise due to the second parasitic capacitance Cp2 is easily removed or compensated since it is a calculable value. That is, an effect from the external noises can minimized and the accuracy of detection of a fingerprint can be improved by interposing the shield layer SL between the first conductive layer M1 and the second conductive layer M2.

The second to fourth conductive layers M2 to M4 configure the gain controller <NUM> that determines the amount of feedback capacitance of the amplifier A, which will be described hereinafter, in detail.

The second conductive layer M2 and the third conductive layer M3 include the first feedback capacitance electrode <NUM> and a second feedback capacitance electrode <NUM>. The first feedback capacitance electrode <NUM> is connected to the first input N1 of the amplifier A, and the second feedback capacitance electrode <NUM> is connected to the output N2 of the amplifier A. A plurality of sub-feedback capacitances Cfb_1, Cfb_2, Cfb_3, and Cfb_4 are formed between the first feedback capacitance electrode <NUM> and the second feedback capacitance electrode <NUM>. The second feedback capacitance electrode <NUM> is composed of sub-electrodes 117_1, 117_2, 117_3, and 117_4, and an end of each of the sub-feedback capacitances Cfb_1, Cfb_2, Cfb_3, and Cfb_4 is connected to a respective one of the sub-electrodes 117_1, 117_2, 117_3, and 117_4. The amounts of the sub-feedback capacitances Cfb_1, Cfb_2, Cfb_3, and Cfb_4 are the same or different. For example, when the amount of a first sub-feedback capacitance Cfb_1 is X, the amounts of second to fourth sub-feedback capacitances Cfb_2, Cfb_3, and Cfb_4 may be respectively X2, X3, and X4, but are not limited thereto.

The sub-electrodes 117_1, 117_2, 117_3, and 117_4 configuring the second feedback capacitance electrode <NUM> are formed depending on the number of the sub-feedback capacitances Cfb_1, Cfb_2, Cfb_3, and Cfb_4. In the drawings, four sub-feedback capacitances Cfb_1, Cfb_2, Cfb_3, and Cfb_4 are exemplarily described, however, the number of the sub-feedback capacitances Cfb_1, Cfb_2, Cfb_3, and Cfb_4 may be changed, and accordingly the number of the sub-electrodes 117_1, 117_2, 117_3, and 117_4 configuring the second feedback capacitance electrode <NUM> may be changed. Each of the sub-electrodes 117_1, 117_2, 117_3, and 117_4 is selectively connected to the output N2 of the amplifier A. That is, the sub-electrodes 117_1, 117_2, 117_3, and 117_4 may be selectively connected to the output N2 of the amplifier A by a plurality of fourth switches S4_1, S4_2, S4_3, and S4_4. Accordingly, only some of the sub-feedback capacitances Cfb_1, Cfb_2, Cfb_3, and Cfb_4 are selected, and a composite capacitance of the selected sub-feedback capacitances Cfb_1, Cfb_2, Cfb_3, and Cfb_4 may function as the feedback capacitance of the amplifier A. For example, assuming that the first sub-feedback capacitance Cfb_1 and the second sub-feedback capacitance Cfb_2 are selected, a capacitance in which the two sub-feedback capacitances are combined in parallel functions as the feedback capacitance of the amplifier A.

The output voltage Vout of the amplifier A may vary depending on the amount of a feedback capacitance, and more specifically, may be expressed as follows. Here, Vdrv is the amount of a driving voltage applied to an external electrode (reference numeral <NUM> of <FIG>). In addition, Cdrive is an input capacitance of the amplifier A, i.e. a capacitance in which a capacitance formed between the sensing electrode <NUM> and the finger F, a capacitance formed by the molding layer m, etc. are combined in series.

That is, since the output voltage Vout of the amplifier A is inversely proportional to the amount of a feedback capacitance Cfb determined by the gain controller <NUM>, and the amount of the feedback capacitance varies by the fourth switches S4_1, S4_2, S4_3, and S4_4, the range of the output voltage Vout of the amplifier A may be changed.

For example, when it is necessary to increase fingerprint detection sensitivity (when it is necessary to widen an output voltage range of an amplifier), some of currently connected sub-feedback capacitances Cfb_1, Cfb_2, Cfb_3, and Cfb_4 are disconnected using the fourth switches S4_1, S4_2, S4_3, and S4_4 so as to decrease the amount of the feedback capacitance. On the contrary, when it is necessary to decrease fingerprint detection sensitivity (when it is necessary to narrow an output voltage range of an amplifier), some of currently disconnected sub-feedback capacitances Cfb_1, Cfb_2, Cfb_3, and Cfb_4 are further connected using the fourth switches S4_1, S4_2, S4_3, and S4_4 so as to increase the amount of the feedback capacitance. That is, since the feedback capacitance of the amplifier A varies by the gain controller <NUM>, fingerprint detection sensitivity can be optimized.

The fingerprint detecting apparatus may be installed in various kinds of devices. A power supply voltage, a thickness of a coating layer, etc. may vary according to the kinds of the devices. In addition, they are affected by environmental factors, such as a power supply noise, a package noise, an external noise, etc. in different degrees. According to various embodiments of the present invention, sensitivity can be optimized by adjusting the amount of the feedback capacitance of the amplifier A according to the differences generated by the various factors.

For example, fingerprint detection sensitivity is affected by a thickness of the molding layer m formed on the first conductive layer M1. The sensitivity is increased by decreasing the feedback capacitance of the amplifier A when it is necessary to form a thick molding layer m by design. On the contrary, the sensitivity is optimized by relatively increasing the feedback capacitance of the amplifier A when it is fine to form a thin molding layer.

Meanwhile, the second switch S2 is connected between the first input N1 and the output N2 of the amplifier A. The second switch S2 is a switch for resetting the feedback capacitance of the amplifier A. The second switch S2 is turned on in a preparation step for detection of a fingerprint, and turned off during detection of a fingerprint. The operation of the switches will be described later, in detail.

The second conductive layer M2 includes a guard ring G2 surrounding the first feedback capacitance electrode <NUM>. The guard ring G2 is connected to the ground potential or another appropriate potential to block interference from an adjacent sensing pixel. Although the guard ring G2 is described to have a ring shape in this embodiment, but is not limited thereto. The guard ring G2 may be formed in various shapes, such as a circular shape, a non-circular shape, a polygonal shape, etc. and formed as a protection electrode to minimize interference from an adjacent metal.

A guard ring G3 is formed adjacent to between the sub-electrodes 117_1, 117_2, 117_3, and 117_4 of the second feedback capacitance electrode <NUM>, and to the entire second feedback capacitance electrode <NUM>. The guard ring G3 is connected to the ground potential or another appropriate potential to minimize of generation of a parasitic capacitance due to a relationship between adjacent sub-electrodes 117_1, 117_2, 117_3, and 117_4. In addition, generation of a parasitic capacitance due to a relationship with an adjacent fingerprint sensor device <NUM> can be minimized. A plurality of guard rings G3 may be formed. Although the guard ring G3 is described to have a ring shape in this embodiment, but is not limited thereto. The guard ring G1 may be formed in various shapes, such as a circular shape, a non-circular shape, a polygonal shape, an unconnected wall shape, etc. and formed as a protection electrode to minimize interference from an adjacent metal.

According to an embodiment of the present invention, the guard ring G3 may be formed in the third conductive layer M3, like the sub-electrodes 117_1, 117_2, 117_3, and 117_4 of the second feedback capacitance electrode <NUM>. However, according to another embodiment of the present invention, the guard ring G3 may not be formed at the same level in method as the sub-electrodes 117_1, 117_2, 117_3, and 117_4. In this case, as shown in <FIG>, the guard ring G3 may be formed at a little bit lower level or a little bit higher level than the sub-electrodes 117_1, 117_2, 117_3, and 117_4. When the guard ring G3 is formed at a different level height, a more prominent effect to prevent generation of a parasitic capacitance between the adjacent sub-electrodes 117_1, 117_2, 117_3, and 117_4 can be obtained. According to still another embodiment of the present invention, the guard ring G3 may be omitted.

Meanwhile, the sub-electrodes 117_1, 117_2, 117_3, and 117_4 may be formed at different levels from each other. That is, although the sub-electrodes 117_1, 117_2, 117_3, and 117_4 are described to be formed at the same plane in <FIG> and <FIG>, the sub-electrodes 117_1, 117_2, 117_3, and 117_4 may be formed at different levels from each other according to another embodiment of the present invention.

Meanwhile, the third conductive layer M3, i.e. the sub-electrodes and the guard ring G3 may be formed as part of a metal-insulator-metal (MIM) structure.

By manufacturing the third conductive layer M3 including the plurality of sub-electrodes 117_1, 117_2, 117_3, and 117_4 as part of the MIM structure, the accuracy can be improved, and even when the number of sub-electrodes 117_1, 117_2, 117_3, and 117_4 increases, an influence therebetween, such as short or interference, can be prevented.

The fourth conductive layer M4 is formed under the third conductive layer M3. As described above, the plurality of sub-feedback capacitances Cfb_1, Cfb_2, Cfb_3, and Cfb_4 are selectively connected to the output N2 of the amplifier by the plurality of fourth switches S4_1, S4_2, S4_3, and S4_4. An end of each of the fourth switches S4_1, S4_2, S4_3, and S4_4 is connected to a respective one of the sub-electrodes 117_1, 117_2, 117_3, and 117_4 of the second feedback capacitance electrode <NUM>, and the other end of the fourth switches S4_1, S4_2, S4_3, and S4_4 is connected to the output N2 of the amplifier A through a lowermost electrode <NUM> included in the fourth conductive layer M4. In addition, the fourth conductive layer M4 may further include an electrode for routing an operating power supply of the amplifier A or other signals, an electrode connected to the ground potential, etc. Another electrode (not shown) included in the third conductive layer M3 may function as an electrode included in the fourth conductive layer M4. In this case, the fourth conductive layer M4 may be omitted. When the fourth conductive layer M4 is omitted, the other ends of the fourth switches S4_1, S4_2, S4_3, and S4_4 are directly connected to the output N2 of the amplifier A.

Hereinafter, operations of the first to third switches S1 to S3 included in a fingerprint detecting apparatus in accordance with an embodiment of the present invention will be described.

<FIG> is a timing chart for describing an operation of each switch in a fingerprint detecting apparatus in accordance with an embodiment of the present invention.

In <FIG>, each of the switches S1 to S3 has an on-state represented as being high, and an off-state represented as being low. In addition, regarding the external electrode, a high state refers to a state in which a driving voltage Vdrv is applied to the external electrode <NUM>, and a low state refers to a state in which a driving voltage Vdrv is not applied. According to an embodiment of the present invention, the driving voltage Vdrv may be a pulse signal controlled by a clock signal, and implemented in various forms, such as an AC voltage or DC voltage with a predetermined frequency, etc..

Referring to <FIG>, first, the second switch S2 is in an on-state during a period T1, and the first switch S1 and the third switch S3 are in an off-state. While the second switch S2 is an on-state, the feedback capacitance of the amplifier A is reset. At this time, since the first switch S1 is in an off-state, a current does not flow from the sensing electrode <NUM> to the first input N1 of the amplifier A. Since the plurality of fingerprint sensor devices <NUM> are arranged at very small intervals in the sensor array <NUM>, each of the fingerprint sensor devices <NUM> is affected by a current flowing through an adjacent fingerprint sensor device <NUM>. That is, when the current flows through the adjacent fingerprint sensor device <NUM>, a parasitic capacitance is generated due to a relationship with the adjacent fingerprint sensor device <NUM>, resulting in an adverse effect on the accuracy of detection of a fingerprint. According to the embodiments of the present invention, when it is not necessary to apply a signal to the first input N1 of the amplifier A, for example, in a preparation step for detection of a fingerprint, etc., the first switch S1 is turned off to block a current flow and minimize an influence on the adjacent fingerprint sensor device <NUM>. For example, while the adjacent fingerprint sensor device <NUM> performing an operation of detection of a fingerprint, a first switch S1 of the corresponding fingerprint sensor device <NUM> is controlled to be in an off-state.

When the reset of the feedback capacitance of the amplifier A is completed, a period T2 starts. The period T2 is a period in which the amplifier A receives a response signal through the sensing electrode <NUM> in accordance with application of the driving voltage Vdrv, to form an output voltage. When the period T2 starts, the first switch S1 is switched to an on-state and prepared to receive the response signal in accordance with application of the driving voltage Vdrv. The application of the driving voltage Vdrv through the external electrode <NUM> may be performed at the same time as the first switch S1 is switched to an on-state, or after thereof. During the period T2, the second switch S2 is in an off-state, and a feedback capacitance is formed in the amplifier A. The amount of the feedback capacitance may be changed, as described above, by the plurality of fourth switches S4_1, S4_2, S4_3, and S4_4 included in the gain controller <NUM>. Meanwhile, during the period T2, the third switch S3 is in an off-state as well.

A period T3 is a period in which the output voltage Vout formed by the amplifier A in the period T2 is output for calculation. During the period T3, the third switch S3 connected to the output N2 of the amplifier A is switched to an on-state, and the first switch S1 and the second switch S2 are in an off-state.

The third switch S3 maintains the on-state for an appropriate time in order to sufficiently transmit the response signal in accordance with the driving voltage Vdrv applied through the external electrode <NUM>. For example, the third switch S3 maintains the on-state until a potential of the external electrode <NUM> falls to <NUM> V (or a ground voltage). The period in which the driving voltage Vdrv is applied through the external electrode <NUM>, and the period in which the third switch S3 maintains the on-state may overlap or not, as shown in the drawing.

<FIG> is a diagram for describing a configuration of the fingerprint sensor device <NUM> of <FIG> in accordance with a second embodiment of the present invention.

Referring to <FIG>, a plurality of fingerprint sensor devices <NUM> are arranged to form columns and rows, and configure a sensor array in the second embodiment of the present invention as well. Comparing to the first embodiment described with reference to <FIG>, the external electrode (<NUM>, see <FIG>) is omitted, and a single fingerprint sensor device <NUM> includes a driving voltage applying electrode 111_1 and a sensing electrode 111_2.

According to the second embodiment of the present invention, a driving voltage Vdrv is applied through the driving voltage applying electrode 111_1 of each fingerprint sensor device <NUM>, a response signal from a finger F is input to a first input N1 of an amplifier A through the sensing electrode 111_2. That is, it is understood that the driving voltage applying electrode 111_1 of the fingerprint sensor device <NUM> in the second embodiment functions as the external electrode <NUM> in the first embodiment.

In addition, ESD protection circuits 114_1 and 114_2 may be formed at a path through which a driving voltage Vdrv is applied to the driving voltage applying electrode 111_1 in addition to between the sensing electrode 111_2 and the amplifier A. Other configurations are the same as those described in <FIG>, and descriptions thereof are omitted herein.

<FIG> and <FIG> are cross-sectional view and a perspective view showing a configuration of the fingerprint sensor device <NUM> of <FIG>.

Referring to <FIG> and <FIG>, configurations of the fingerprint sensor device <NUM> in accordance with the second embodiment of the present invention are the same as those of the fingerprint sensor device <NUM> in accordance with the first embodiment of the present invention, except a configuration of a first conductive layer M1.

The first conductive layer M1 includes the driving voltage applying electrode 111_1 and the sensing electrode 111_2. As described above, a driving voltage Vdrv is applied to the driving voltage applying electrode 111_1, and the sensing electrode 111_2 transmit a response signal from the finger F in accordance with application of the driving voltage Vdrv to the first input N1 of the amplifier A. That is, the sensing electrode 111_2 is connected to the first input N1 of the amplifier A, and the connection is turned on/off by a first switch S1. Operations of first to third switches S1 to S3 are the same as described with reference to <FIG>. A guard ring G1 is formed in a periphery of the driving voltage applying electrode 111_1 and a periphery of the sensing electrode 111_2. Since the guard ring G1 is formed between the driving voltage applying electrode 111_1 and the sensing electrode 111_2 as well, generation of a parasitic capacitance due to the relationship between the driving voltage applying electrode 111_1 and the sensing electrode 111_2 can be suppressed.

Descriptions of second to fifth conductive layers M2 to M5 are the same as described in the first embodiment of the present invent, and thus omitted herein.

In a feedback capacitive sensing type fingerprint detecting apparatus in accordance with the embodiments of the present invention, since a feedback capacitance of an amplifier is variable, fingerprint detecting sensibility can be variably optimized depending on the circumstances.

Claim 1:
A fingerprint detecting apparatus, comprising:
a sensor array (<NUM>) comprising a plurality of fingerprint sensor devices (<NUM>) arranged in columns and rows, wherein each of the fingerprint sensor devices (<NUM>) comprises a conductive layer (M1) with a driving voltage applying electrode (111_1) and a sensing electrode (111_2) formed in the conductive layer (M1);
a first guard ring (G1) formed about a periphery of the driving voltage applying electrode (111_1) and a periphery of the sensing electrode (111_2), the first guard ring being formed, in the conductive layer, between the driving voltage applying electrode and the sensing electrode;
a second guard ring surrounding the sensing electrode (111_2) and the first guard ring (G1); and
an amplifier (A) configured to receive a response signal and generate an output signal,
wherein a driving voltage (Vdrv) is applied to a subject through the driving voltage applying electrode (111_1) and the response signal is input to the amplifier (A) through the sensing electrode (111_2).