KR20160044972A - Fingerprint detecting apparatus canceling offset and control method thereof - Google Patents

Abstract

An objective of the present invention is to prevent acquisition of a dark or a light fingerprint and allow an entire image of a fingerprint in a single fingerprint image to have uniform quality. According to an embodiment of the present invention, a fingerprint detecting apparatus comprises: a plurality of sensor pads to output response signals from fingers for a drive signal; a reference voltage providing unit to provide a reference voltage; and an offset adjustment unit to adjust an average voltage level of the response signals from the sensor pads based on the reference voltage.

Description

FIELD OF THE INVENTION [0001] The present invention relates to an offset-

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a fingerprint detecting device and a driving method thereof, and more particularly to a fingerprint detecting device for obtaining a fingerprint image of a constant quality by removing an offset of an output signal, ≪ / RTI >

Since fingerprints vary from person to person, they are widely used in the field of personal identification. In particular, fingerprints are widely used in various fields such as finance, crime investigation and security as personal authentication means.

A fingerprint recognition sensor has been developed to recognize these fingerprints and identify them. The fingerprint recognition sensor is a device for recognizing a fingerprint of a finger by contacting a finger of a person, and is used as a means for determining whether or not the user is a legitimate user.

Various recognition methods such as an optical method, a thermal sensing method, and a capacitive sensing method are known as a method of implementing a fingerprint recognition sensor. Among them, the capacitive type fingerprint recognition sensor acquires the shape of the fingerprint (fingerprint pattern) by detecting a change in capacitance depending on the shape of the ridge and the ridge of the finger when the finger surface of the person touches the conductive detection pattern.

In recent years, various additional functions utilizing personal information such as finance and security have been provided not only in communication functions such as telephone and text message transmission service through portable devices, but also in the necessity of locking devices of portable devices. . In order to improve the locking effect of such a portable device, a terminal equipped with a locking device through fingerprint recognition is being developed in earnest.

1 is a view showing the structure of a basic fingerprint recognition sensor.

In order to detect a change in capacitance due to ridges and ridges of a fingerprint in a capacitive fingerprint recognition sensor, a drive signal (V _drv ) is applied to the bezel 10 surrounding the recognition sensor as shown in FIG. 1, The voltage output through the sensor pad 20 constituting the finger and sensor array was sensed and compared with the output voltage when the finger was not in contact.

Equation (1) is a formula for obtaining the voltage magnitude according to the ridges and ridges of the fingerprint in the fingerprint recognition sensing structure of FIG.

Referring to Equation (1), V _out is the output voltage, V _ref is the reference voltage, and C _FB means the capacitance of the feedback capacitor. V _drv is the driving voltage and C _finger is the capacitance formed when the finger touches the sensor pad.

In the conventional fingerprint recognition sensor, even when the same finger fingerprint is brought into contact with the sensor pad 20, the offsets generated in the fingerprint recognition element serving as the basic unit constituting the fingerprint recognition sensor are different from each other, The quality of the final fingerprint image is deteriorated. That is, even when the same fingerprint is in contact with the sensor pad 20, the voltage value of the sensor pad 20 corresponding to each part of the fingerprint continuously changes due to the offset.

Therefore, in order to prevent such a problem, there has been a need for a method of constantly converting the voltage level obtained by removing the offset included in the value of the output voltage as described above.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems of the prior art.

The object of the present invention is to prevent the dark or faint fingerprints from being obtained by adjusting the offset of the voltage value occurring in the sensor array and to ensure that the entire image of the fingerprint has a constant quality even in one fingerprint image.

According to an aspect of the present invention, there is provided a display device including: a plurality of sensor pads for outputting response signals from a finger to a driving signal; A reference voltage supplier for providing a reference voltage; And an offset adjusting section for adjusting an average voltage level of a response signal from each sensor pad based on the reference voltage.

The fingerprint detecting apparatus may further include a switch for initializing a reference voltage node to which the reference voltage providing unit is connected and a response signal input node to which a response signal from the plurality of sensor pads is inputted to the same voltage.

Wherein the reference voltage supply unit includes: a transistor having an input voltage applied to a drain electrode and a gate electrode connected to a reference voltage node to which the reference voltage is applied; And a resistor having one end connected to the source electrode of the transistor and the other end connected to the reference voltage node.

The fingerprint detection device includes: a sensing circuit that outputs a response signal from each of the plurality of sensor pads; A sample and hold unit for sampling the response signal; An offset canceling unit that includes the reference voltage providing unit and the offset adjusting unit and removes an offset between the sampled response signals; And an analog-to-digital converter for converting the offset-removed signal into a digital signal.

Wherein the offset adjustment unit includes: a transistor having a reference voltage node to which the reference voltage is applied and a drain electrode connected to each other, and a gate electrode connected to the input node; A first capacitor connecting an input terminal to which a response signal from the sensor pad is input and a response signal input node; And a second capacitor connecting the reference voltage node and the response signal input node.

The fingerprint detection device may further include an amplifier for amplifying an output signal from the offset adjustment unit.

According to another aspect of the present invention, there is provided a method of operating a fingerprint detection apparatus including a plurality of sensor pads for outputting response signals from a finger in response to application of a driving signal, step; Comparing the magnitude of the response signal from the plurality of sensor pads with the reference voltage to determine an offset adjustment value; And adjusting an average voltage level of a response signal from the plurality of sensor pads to the reference voltage based on the offset adjustment value.

According to the embodiment of the present invention, by adjusting the response signal from the plurality of sensor pads to a certain level of voltage, a fingerprint image of constant quality can be obtained.

According to another embodiment of the present invention, the offset-adjusted output value can be amplified so that the difference between the signal obtained from the ridges of the fingerprint and the ridge can be greatly amplified without noise.

According to the fingerprint detection apparatus of the present invention, the fingerprint authentication rate for the same fingerprint can be further improved by obtaining a fingerprint image of a constant quality.

It should be understood that the effects of the present invention are not limited to the above effects and include all effects that can be deduced from the detailed description of the present invention or the configuration of the invention described in the claims.

1 is a view showing the structure of a basic fingerprint recognition sensor.
2 is a block diagram schematically showing the entire configuration of a fingerprint detecting apparatus according to an embodiment of the present invention.
FIG. 3 is a diagram illustrating a response signal differentiated by the influence of an offset generated for each sensor pad according to an operation environment of the fingerprint detection device, according to an embodiment of the present invention.
4 is a diagram illustrating an embodiment of an offset removal unit according to an embodiment of the present invention.
FIG. 5 is a diagram illustrating a form in which an amplifier is added to an offset removing unit according to an embodiment of the present invention. FIG.
FIG. 6 is a diagram schematically illustrating a state where an offset of a response signal in various states is removed and amplified according to an embodiment of the present invention. Referring to FIG.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification.

Throughout the specification, when a part is referred to as being "connected" to another part, it includes not only "directly connected" but also "indirectly connected" . Also, when an element is referred to as "comprising ", it means that it can include other elements, not excluding other elements unless specifically stated otherwise.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

2 is a block diagram schematically showing the entire configuration of a fingerprint detecting apparatus according to an embodiment of the present invention.

2, the fingerprint detection apparatus according to one embodiment includes a bezel 110, a sensor pad 120, a sensor array 130, a sensing circuit 140, a sample and hold unit 150, 160, and an ADC 170.

The bezel 110 is a rim surrounding the fingerprint detection device. According to an embodiment, a drive signal is applied to the finger through the bezel, and the plurality of sensor pads 120 receive a response signal to the drive signal from the finger . According to another embodiment, a ground terminal is connected to the bezel 110 so that noise from the periphery does not affect the sensor pads, and the sensor pads 120 transmit drive signals to fingers touching the fingerprint detection device And then receive the response signal.

The bezel 110 may be formed of various materials such as plastic, metal, and the like, and may be configured to protrude from at least a part of the edge of the sensor for performing fingerprint detection. In some electronic devices, the bezel 110 does not exist, and other components in the fingerprint detection device may perform the role of transmitting driving signals to the plurality of sensor pads 120. [

The sensor pad 120 according to an embodiment is a basic unit for recognizing a change in capacitance due to ridges and ridges of the fingerprint fingerprint. At least one sensor pad 120 is connected to the sensing circuit 140, It is possible to sense a response signal from the sensor.

The plurality of sensor pads 120 may be circular, rectangular, or rhombic, but may be other shapes or may be polygonal shapes in a uniform shape. The sensor pads 120 may be arranged in the form of a matrix of adjacent polygons.

The capacitance formed between the finger and the sensor pad 120 may have a different value depending on which part of the finger is touched to the sensor pad 120 when the finger of the person is brought into contact with the fingerprint detection device.

Specifically, the capacitances formed by the valleys and the ridges of the fingerprint fingerprint are different, and the fingerprint detection device obtains the fingerprint image through the difference in capacitance.

The sensor array 130 according to an exemplary embodiment may include a plurality of sensor pads 120 arranged in a plurality of rows and columns and may output a response signal output from the plurality of sensor pads 120 to a sensing circuit (140).

The sensing circuit 140 according to an exemplary embodiment of the present invention is a circuit to which an output signal from the sensor pads 120 is inputted and transmits the output signal to the sample and hold unit 150. According to one embodiment, the sensing circuit 140 may include at least one amplifier and at least one impedance element to amplify and output the response signal based on the gain and impedance magnitude of the amplifier.

One sensing circuit 140 may be provided for each sensor pad 120 constituting the fingerprint detecting device according to one embodiment. Alternatively, a plurality of sensor pads 120 may be provided to one sensing circuit 140 according to another embodiment. An output signal from the group may be input.

The sample and hold unit 150 samples data of a response signal output from the sensing circuit 140, holds the sampled data, and stores the sampled data. The sampling period of the sample and hold unit 150 is controlled by a predetermined clock signal.

The offset removing unit 160 adjusts the offset of the output data of the sample and hold unit 150. The offset eliminator 160 includes a reference voltage supplier 161 for providing a reference voltage of a constant level and a reference voltage supplier 161 for supplying a response signal obtained from the sample and hold unit 150 to the reference voltage supplier 161 And an offset adjusting unit 162 for adjusting the reference voltage level to a predetermined reference voltage level.

The reference voltage supply unit 161 adjusts the voltage input from the voltage supply circuit in the fingerprint detection device to a predetermined level to provide a reference voltage for offset elimination.

For example, when the voltage supply circuit in the fingerprint detection device supplies 5V to the offset removal section 160, the voltage of 5V inputted is 4.8V or 5.1 V, < / RTI > When the average voltage level of the response signal obtained from the sample and hold unit 150 is higher than the reference voltage when the reference voltage is 5 V, the reference voltage providing unit 161 lowers the average voltage level of the response signal, The average voltage level of the response signal can be stabilized by performing a negative feedback function.

As described above, the offset removing unit 160 removes the offset included in the unstable average voltage level change of the response signal, which is indicated by the operation state of the fingerprint detecting device, based on the reference voltage, so that the quality of the fingerprint image acquired by the fingerprint detecting device Can be improved.

The offset adjuster 162 may adjust the average voltage level of the response signal from each sensor pad 120 based on the reference voltage provided by the reference voltage supplier 161. [

The signal average voltage level of the response signal output from each sensor pad 120 by the sensor pad 120, the sensor array 130, the sensing circuit 140, etc., It can be changed continuously.

The operating environment of each sensor pad 120 itself is determined by the position of the sensor pad 120 in the sensor array 130, the difference in design of the sensor pad 120 caused by the process design, Which may be different. Accordingly, the offset of the response signal output from each sensor pad 120 becomes different, and the offset may not be uniform over time even in one sensor pad 120. FIG.

The offset adjusting unit 162 adjusts an offset generated in the above-described manner in real time to remove an offset by adjusting an average voltage level of a response signal in each sensor pad 120 to a reference voltage.

According to the above description, since the operation of the offset removal unit 160 can remove the offset generated according to the operation of the sensor pad 120 when the same fingerprint is in contact with the fingerprint detection device, It is also possible to eliminate a change in offset due to characteristics and external environment.

The ADC (Analog to Digital Converter) 170 can perform a function of digitizing the sensing data of the analog form. The data converted into digital form through the ADC 170 is stored in the memory of the fingerprint detection device, and the fingerprint detection device can acquire the fingerprint image through the corresponding data converted into the digital form.

The fingerprint detection apparatus according to an exemplary embodiment may include a driver, and the driver may include a fingerprint information processing unit, a memory, a controller, and the like, and may be implemented with one or more integrated circuit (IC) chips.

The memory can store data converted into digital form through the ADC 170 and predetermined data or real-time received data used for fingerprint position detection, area calculation of the fingerprint, division of ridges and ridges of fingerprint images, and the like.

The fingerprint information processing unit can generate necessary information by calculating the contact of the fingerprint, the area of the fingerprint touched, and the ridge and ridge division of the fingerprint through the voltage value of the digital format data stored in the memory.

The control unit may include a micro control unit (MCU), and performs a unique function in the sample and hold unit 150, the offset removal unit 160, the ADC 170, the fingerprint information processing unit, Off of the switch included in the offset removal unit 160, and the like. The control unit can perform the determined signal processing through the firmware.

FIG. 3 illustrates a response signal differentiated by the influence of an offset generated for each sensor pad 120 according to an operation environment of the fingerprint detection device, according to an embodiment of the present invention.

The parasitic capacitance C _p in FIG. 3 means a capacitance attached to the sensor pad 120, which is a kind of parasitic capacitance formed by the sensor pad 120, the signal wiring constituting the fingerprint detection device, and the like. The parasitic capacitance C _p may include any parasitic capacitance generated by the bezel 110, the sensor array 130, or the periphery.

The air capacitance C _air in FIG. 3 is a capacitance formed between the finger pad fingerprint and the sensor pad 120. Since the electrostatic capacitance increases as the distance decreases, the air capacitance C _air decreases as the distance between the fingerprint valley and the sensor pad 120 increases.

Assume that FIG. 3 (a) is an average fingerprint recognition situation. The sum of the capacitance C _ridge and the parasitic capacitance C _p formed between the ridge of the finger fingerprint and the sensor pad 120 is the sum of the valley of the fingerprint finger and the sensor pad 120 (C _air ) and the parasitic capacitance (C _p ), which are formed between the first and second electrodes.

In the above Equation 1, C _finger is an electrostatic capacitance formed when a finger touches the sensor pad 120, and is divided into C _{finger_ridge} and C _{finger_valley} values depending on which portion of the ridge of the finger is in contact. In equation (1), the output voltage, V _out, is a different output, such as V _ridge and V _valley , depending on which of C _{finger_ridge} and C _{finger_valley} values are applied to C _finger .

That is, the fingerprint detection apparatus can discriminate the difference when the ridge and the ridge contact the sensor pad 120 through the difference between the V _ridge and the V _valley .

The difference between the electrostatic capacity formed between the ridges of the fingerprint and the sensor pad 120 and the capacitance formed between the fingerprint of the fingerprint and the sensor pad 120 is determined by the state of the fingerprint, The external environment or the environment of each sensor pad 120 (e.g., the position of the sensor pads, the difference between the sensor pads generated by the process design), and the like, The average level of the voltage value may be different.

For example, the difference between V _ridge and V _valley remains 0.2V, but in some cases, each value can be 1.0V and 0.8V (average level 0.9V), while in other cases 0.6V and 0.4V Average level 0.5V), the difference may be to maintain 0.2V. A problem may occur such that a part of the fingerprint image acquired by the fingerprint detection device becomes darker or blurred depending on the average level difference of the voltages, that is, the offset. That is, a pixel variation of each sensor pad 120 itself occurs according to an operation environment of the sensor array 130 or a design process, and an offset change of a response signal occurs. As a result, The output fingerprint image may appear to be fluctuated (a fluctuated fingerprint image).

As shown in FIG. 3 (b), the voltage levels obtained by the sensor pads 120 also vary according to the pixel variation according to the operating environment of each sensor pad 120 itself. If the fingerprint image having a constant average voltage level of the output signal is extracted or amplified as it is, not only the noise can be efficiently removed but also the quality of the outputted fingerprint image may be deteriorated.

Thus, in order to keep the voltage level acquired by the fingerprint detection device in accordance with the capacitance change between the fingerprint fingerprint and the sensor pad 120 constant under the different operating environment of the fingerprint detection device, the average voltage level obtained from the sensor pad 120 The offset eliminator 160 is required to remove the offset of the reference voltage and to output a signal having a constant reference voltage.

4 is a diagram illustrating an embodiment of an offset removal unit 160 according to an embodiment of the present invention.

Referring to FIG. 4, the offset removing unit 160 may include a reference voltage providing unit 161 and an offset adjusting unit 162.

According to an embodiment, the reference voltage providing unit 161 may include a second transistor M2 and a resistor R1, and the offset adjusting unit 162 may include a first transistor M1, And capacitors C1 and C2.

The first and second transistors M1 and M2 in the present invention may be a field effect transistor and may include a gate, a source, and a drain electrode.

Offset look at the arrangement of the removal unit 160, a reference voltage supply unit a second drain electrode of the transistor (M2) there can be applied the input voltage (V _DD), the input voltage (V _DD) in 161 is the fingerprint detection And can be controlled by a control unit of the apparatus. A resistor R1 may be connected to the source electrode of the second transistor M2 and the other of the resistor may be connected to the second node N2 and the reference voltage node together with the gate electrode of the second transistor M2. have.

The drain electrode of the first transistor M1 in the offset adjustment unit 162 is connected to the second node N2 and the reference voltage node is connected to the reference voltage supply unit 161 May be maintained at the provided reference voltage Vref and vary according to the input value Vin of the offset eliminator 160 to have the output value Vout of the offset eliminator 160. [ The source electrode of the first transistor M1 is connected to the ground potential and the gate electrode of the first transistor M1 may be connected to the first and second capacitors C1 and C2 through a first node N1 .

The response signal from the sample and hold unit 150 becomes the input value Vin of the offset removal unit 160 and is supplied to the first node C1 through the first capacitor C1, (N1, response signal input node).

The second capacitor C2 is connected between the first node N1 (the response signal input node) through which the input value Vin is inputted through the first capacitor C1 and the output value Vout which is the final output of the offset eliminator 160, And a second node N2 (a reference voltage node).

Hereinafter, the reference voltage supplier 161 and the offset adjuster 162 constituting the offset eliminator 160 will be described.

The second transistor M2 in the reference voltage supplier 161 is controlled such that the input voltage V _DD input from the drain electrode maintains a constant reference voltage Vref formed through the second transistor M2 and the resistor R1 . For example, when the reference voltage Vref is decreased, the gate voltage of the second transistor M2 is also decreased. As a result, the drain current is decreased, and the amount of voltage drop in the resistor R1 is reduced. Vref may be increased to maintain the reference voltage Vref.

On the contrary, when the reference voltage Vref increases, the gate voltage of the second transistor M2 also increases to increase the drain current, so that the voltage drop in the resistor R1 increases and the reference voltage Vref decreases again can do.

The second transistor M2 in the reference voltage supplier 161 operates as a variable resistor so that the reference voltage Vref changes according to the operating environment of the fingerprint detecting device and the difference between the sensor pads 120 itself Can be prevented.

The offset adjusting unit 162 includes a first transistor M1 and first and second capacitors C1 and C2. The offset adjusting unit 162 may cause the input value Vin of the offset removing unit 160 to be positioned at the reference voltage Vref level value provided by the reference voltage providing unit 161 so that the offset of the output voltage Vout Can be adjusted.

The operation of the offset adjusting unit 162 will be described. For example, the first and second nodes N1 and N2 (response signal input node, reference voltage node) before the offset removing unit 160 performs the initial operation are the same It can be set to a potential. As the first and second nodes N1 and N2 (response signal input node, reference voltage node) have the same potential, there may not be a charged amount of charge in the second capacitor C2.

 According to one embodiment, in order to equalize the potentials of the first and second nodes (N1, N2: response signal input node, reference voltage node), there is a switch such as S1 in the drawing, May be short-circuited before performing the initial operation, and may be switched to an open state upon operation of the offset eliminator 160. The switch S1 can be turned on / off by the control unit in the fingerprint detection device.

When the input value Vin of the offset eliminator 160 is applied in the above state, the first and second capacitors C1 and C2 are charged through the difference between the input value Vin and the reference voltage Vref And the first transistor M1 can output a voltage value that causes the amount of change of the input value Vin to change by using the reference voltage Vref as an average value.

More specifically, the input value Vin applied to the offset removal unit 160 from the sample and hold unit 150 is compared with the reference voltage Vref, which is the initial voltage of the first node N1 (response signal input node) And the voltage of the first node N1 (response signal input node) changes due to the charge. Since the first node N1 and the response signal input node are connected to the gate electrode of the first transistor M1, the current value of the drain electrode changes as the gate electrode voltage of the first transistor M1 changes, The voltage value changed by the voltage Vref of the second node N2 (reference voltage node) may become the output value Vout of the offset eliminator 160 due to the influence. However, since the reference voltage supply unit 161 including the second transistor M2 and the resistor R1 is intended to maintain a constant voltage at the second node N2 (reference voltage node), only the change amount of the input value Vin The effect is obtained that the difference between the input value Vin and the reference voltage Vref, that is, the offset of the output voltage Vout, is removed.

The output value Vout thus output is transferred from the offset eliminator 160 to the ADC 170 and converted into digital data by the ADC 170 to be used for acquiring a fingerprint image.

As described above, the quality of the fingerprint image acquired by the fingerprint detection device can be improved through the offset removal unit 160. In particular, as the average level of the input value Vin of the offset eliminator 160 is adjusted to the reference voltage Vref, the quality of the obtained fingerprint image can be improved.

It is ideal that each sensor pad 120 in the fingerprint detection device should be produced with the same specifications and show the same performance. However, the position of the sensor pad 120 in the sensor array 130, An offset may occur in the output signal of the sensor pad due to the difference, the operation status of the fingerprint detection device, and the external environment. If such an offset is not removed, the quality of the fingerprint image may be deteriorated, such that some of the fingerprint image may be acquired blurred and some of the fingerprint image may be obtained darkly, and if the output is amplified without the offset being removed, A noise image that is not related to the fingerprint may be included in the fingerprint image that is acquired because the noise is not efficiently removed.

Thus, by adjusting the average voltage level of the response signal to the reference voltage through the offset eliminator 160 of the present invention, even if the fingerprint detection device operates under any circumstances, pixel variation of the image.

5 is a diagram illustrating an embodiment in which an amplifier is added to the offset eliminator 160 according to an embodiment of the present invention.

According to the embodiment of FIG. 5, an amplifier may be added to the output of the offset eliminator 160 to amplify the output voltage from which the offset from the reference voltage is removed. The amplifier can amplify and output the input, and perform the role of lowering the output resistance in addition to the function of amplifying the signal. According to another embodiment, the amplifier may be replaced by other elements such as a plurality of buffers capable of signal amplification or signal anchoring.

According to one embodiment, the offset in the offset eliminator 160 is removed and the response signal output based on the constant reference voltage is amplified, so that only the difference in voltage depending on the ridge and ridge of the fingerprint of the finger is amplified The fingerprint image can be obtained by detecting a change in the electrostatic capacity, thereby obtaining an image having a clear difference between the ridge and ridge portions of the fingerprint.

According to one embodiment, a plurality of amplifiers may be constituted by being connected in series. For example, by using a two-stage amplifier with two amplifiers connected, a larger voltage gain can be obtained and noise can be reduced than when using one amplifier.

FIG. 6 is a diagram schematically illustrating a state where an offset of a response signal in various states is removed and amplified according to an embodiment of the present invention. Referring to FIG.

Referring to FIG. 6A, response signals to the same input between the sensor pads 120 may form different offsets according to changes in the operating environment between the sensor pads 120.

Referring to FIG. 6 (b), the response signals are adjusted in offset from the offset eliminator 160 through the sample and hold unit 150, with respect to the reference voltage. According to one embodiment, the average of the voltage of the response signal may be the reference voltage, and the offset may be adjusted so that the start voltage of the response signal applied to the offset removal unit 160 becomes the reference voltage.

More specifically, the offset adjuster in the offset eliminator 160 compares the reference voltage level provided in the reference voltage supply and the voltage level of the response signal from the plurality of sensor pads 120, If it is lower than the reference voltage, the voltage of the response signal is raised by the corresponding difference, and in the opposite case, the voltage of the response signal is lowered.

Referring to FIG. 6 (c), the response signal in which the voltage offset is adjusted may be amplified by the amplifier included in the offset eliminator 160, so that the difference in the response signal can be more emphasized.

The offset signal is adjusted through the offset removing unit 160 and the amplified response signal is converted into a digital signal through the ADC 170. The fingerprint detecting apparatus combines the converted digital signals to obtain a fingerprint image. Through the adjustment of the response signal, the obtained fingerprint image may be an image of a constant quality with a minimum offset due to a change in the operating environment of each sensor pad 120, Can be clearly distinguished. Further, by acquiring an image of a constant quality, the authentication of the user performed through the fingerprint detection device is performed quickly, and thus the time required for the user to touch the fingerprint detection device can be shortened.

It will be understood by those skilled in the art that the foregoing description of the present invention is for illustrative purposes only and that those of ordinary skill in the art can readily understand that various changes and modifications may be made without departing from the spirit or essential characteristics of the present invention. will be. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. For example, each component described as a single entity may be distributed and implemented, and components described as being distributed may also be implemented in a combined form.

The scope of the present invention is defined by the appended claims, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included within the scope of the present invention.

110: Bezel
120: Sensor pad
130: sensor array
140: sensing circuit
150: sample and hold section
160: Offset removal
161: Reference voltage supply
162:
170: ADC

Claims (7)

A plurality of sensor pads for outputting response signals from the finger to the driving signal;
A reference voltage supplier for providing a reference voltage; And
And an offset adjusting section for adjusting an average voltage level of a response signal from each sensor pad based on the reference voltage.
The method according to claim 1,
A reference voltage node to which the reference voltage providing unit is connected and a response signal input node to which a response signal from the plurality of sensor pads is inputted to the same voltage.
The method according to claim 1,
Wherein the reference voltage supply unit includes:
A drain electrode to which an input voltage is applied, and a gate electrode connected to a reference voltage node to which the reference voltage is applied; And
Wherein one end of the resistor is connected to the source electrode of the transistor, and the other end of the resistor is connected to the reference voltage node.
The method according to claim 1,
A sensing circuit for outputting a response signal from each of the plurality of sensor pads;
A sample and hold unit for sampling the response signal;
An offset canceling unit that includes the reference voltage providing unit and the offset adjusting unit and removes an offset between the sampled response signals; And
And an analog-to-digital converter for converting the offset-removed signal into a digital signal.
The method according to claim 1,
Wherein the offset adjusting unit comprises:
A transistor having a reference voltage node to which the reference voltage is applied and a drain electrode connected to each other, and a gate electrode connected to the input node;
A first capacitor connecting an input terminal to which a response signal from the sensor pad is input and a response signal input node; And
And a second capacitor for connecting the reference voltage node and the response signal input node.
The method according to claim 1,
And an amplifier for amplifying an output signal from the offset adjustment unit.
And a plurality of sensor pads for outputting a response signal from a finger in accordance with application of a driving signal,
Providing a reference voltage;
Comparing the magnitude of the response signal from the plurality of sensor pads with the reference voltage to determine an offset adjustment value; And
And adjusting an average voltage level of a response signal from the plurality of sensor pads to the reference voltage based on the offset adjustment value.

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