JP2003123059A - Fingerprint authentication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sufficient individual authentication performance even under an on-vehicle environment. SOLUTION: A fingerprint authentication system 10 is provided with an image pickup means (CCD 17) for picking up a fingerprint image and generating and outputting the fingerprint image signals, an analog/digital conversion means (AD 23e) for converting the fingerprint image signals to digital signals, a power supply voltage detection means (power supply voltage sensor 23b) for detecting a power supply voltage supplied to the fingerprint authentication system, a temperature detection means (temperature sensor 20) for detecting an operation temperature of the image pickup means itself or a surrounding ambient temperature, a correction value output means (CPU 23h) for generating and outputting a correction value for the fingerprint image signals on the basis of a power supply voltage detected by the power supply voltage detection means and a temperature detected by the temperature detection means, and a correction means (AMP 23d) for correcting the fingerprint image signals by using the correction value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called fingerprint authentication system for performing personal authentication by "fingerprint" which is a biological characteristic of a human body that cannot be arbitrarily changed.

[0002]

2. Description of the Related Art Fingerprint authentication, which is one of biometric authentications, is a personal authentication method that uses a fingerprint unique to an individual, and has much higher security than a password method or an ID card method. It is a technology. Fingerprint authentication systems using this technology are used in entrance / exit management systems for specific areas in business establishments, home security, payment systems on the Internet, etc., or usage authentication systems for various business applications running on computers. There is.

FIG. 10 is a simplified block diagram of a conventional fingerprint authentication system 1. Generally, the fingerprint authentication system 1 includes an image reading device 2 and a fingerprint matching device 3, and uses a matching result of the fingerprint matching device 3, that is, a personal authentication result,
Whether or not to use the various systems described above, or whether or not to enter or leave the system, etc.
Although the figure shows the fingerprint authentication system 1 of the type in which the image reading device 2 and the fingerprint collation device 3 are separated, an integrated type may be used.

The image reading device 2 is a compact, lightweight, low power consumption image pickup device such as a CCD (Charge Cou
pled Device) type and MOS (Metal-Oxide Semiconducto)
r) type and other two-dimensional solid-state imaging device, and the surface light source (LED:
By illuminating the fingertip of the authentication subject 4 placed on the reading surface (front surface) of the device with light from a light emitting diode, and receiving the reflected light from the fingertip by the photoelectric conversion element array of the device. The fingerprint image is read and the fingerprint image is output to the fingerprint matching device 3.

The fingerprint collation device 3 extracts a feature point (fingerprint end point or branch point) of a fingerprint from a fingerprint image read by the image reading device 2, and the feature point is registered in advance. It is determined whether or not it matches the feature point information of the registered registrant, and the person-to-be-authenticated 4 is authenticated, and the collation result (personal authentication result) is entered / exited to / from a specific area, such as an office. It is output to a management system, home security, a payment system on the Internet, or a usage authentication system for various business applications running on a computer.

As described above, the conventional fingerprint authentication system 1
Due to its excellent safety, is already used in various applications as described above, but it is also considered to be applied to other applications, such as a vehicle antitheft device. In recent years, the number of vehicle theft damages has been increasing, and for example, the anti-theft measures such as so-called immobilizers that allow engine start by electronic ID key verification have been taken. However, none of them can be said to be the ultimate in "personal authentication", and a society that tries to implement more reliable anti-theft measures by installing the fingerprint authentication system 1 that has excellent effects as personal authentication in a vehicle. There is a specific demand.

[0007]

However, when the conventional fingerprint authentication system 1 is mounted on a vehicle as it is,
There is a problem in that the operation of the image reading apparatus 2 cannot withstand the severe operating environment and sufficient personal authentication performance cannot be obtained.

There are various causes, but according to the study by the present inventors, it has been found that the following representative causes cause the deterioration of the personal authentication performance. (1) The light amount of the surface light source changes under the influence of "environmental temperature" and "battery power supply voltage". (2) The brightness level of the image signal output from the two-dimensional solid-state imaging device changes under the influence of variations in "environmental temperature" and "battery power supply voltage". (3) The image signal output from the two-dimensional solid-state imaging device is converted into a digital signal by the AD converter.
The reference potential (clamp potential) of the D converter changes under the influence of "environmental temperature" and "battery power supply voltage".

Therefore, the present invention is based on the above causes (1) to (3).
Pays attention to the fact that both are caused by fluctuations in "environmental temperature" and "battery power supply voltage", and detects fluctuations in "environmental temperature" and "battery power supply voltage" in real time, and It is an object of the present invention to make it possible to obtain sufficient personal authentication performance even in an in-vehicle environment by performing necessary corrections on image signals output from the device.

[0010]

A fingerprint authentication system according to the present invention comprises an image pickup means for picking up a fingerprint image and generating and outputting the fingerprint image signal, and an analog-digital converting means for converting the fingerprint image signal into a digital signal. A fingerprint authentication system comprising: a power supply voltage detecting means for detecting a power supply voltage supplied to the fingerprint authentication system; a temperature detecting means for detecting an operating temperature or an ambient environment temperature of the image pickup means itself; A correction value output unit that generates and outputs a correction value for the fingerprint image signal based on the power supply voltage value detected by the power supply voltage detection unit and the temperature value detected by the temperature detection unit, and a fingerprint using the correction value. And a correction means for correcting the image signal.

According to the present invention, in a high temperature environment (for example, in a car under hot weather where the temperature may reach 70 ° C. or higher), the power supply voltage becomes unstable (fluctuation of the battery power supply voltage). Therefore, it is intended to prevent the accuracy and quality of image reading from being degraded.

The "imaging means" may be a CCD type imaging device or a MOS type imaging device. Further, the "analog / digital conversion means" may be a so-called AD converter that digitally converts and outputs an analog input voltage range based on a predetermined clamp potential. Further, the "power supply voltage detecting means" and the "temperature detecting means" may both be resistance voltage dividing circuits that resistance-divide the power supply voltage and output the same. In this case, the "temperature detecting means" has a predetermined temperature coefficient. And a voltage drop component of the resistance element is output as a temperature value.

According to the present invention, the power supply voltage detection means detects at least the power supply voltage supplied to the image pickup means, and the temperature detection means detects the operating temperature of the image pickup means itself or the ambient environment temperature. Then, a correction value for the fingerprint image signal is generated and output based on the power supply voltage value detected by the power supply voltage detection means and the temperature value detected by the temperature detection means, and the fingerprint image signal is generated using this correction value. Will be corrected.

That is, since the fingerprint image signal photographed by the image pickup means is corrected on the basis of the fluctuation of the power supply voltage and the fluctuation of the ambient temperature under the vehicle environment, the influence of these fluctuation factors can be suppressed. It is possible to improve the accuracy and quality of image reading. As a result, it is possible to realize a fingerprint authentication system capable of obtaining sufficient personal authentication performance even in an in-vehicle environment.

According to a more preferable configuration of the present invention, the correction value output means uses the power supply voltage value and the temperature value as input parameters, and the correction value output means outputs the correction value to the analog-digital conversion means in correspondence with the input parameters. It is supposed to have a correspondence table (for example, a lookup table) that outputs the correction value of the clamp potential of the fingerprint image signal.

With such a configuration, it is necessary to experimentally or empirically obtain the optimum correction value corresponding to various combinations of the power supply voltage and the ambient temperature and store it in the look-up table in advance. Thus, it is possible to easily and quickly generate and output the required correction value without using a complicated model formula or the like.

Further, in a more preferable configuration of the present invention, the correction means is an amplifier circuit inserted in a stage preceding the analog-digital conversion means, and the clamp potential of the fingerprint image signal is adjusted according to the correction value. It is said that.

With such a configuration, the clamp potential of the fingerprint image signal input to the analog-to-digital conversion means is adaptively adjusted with respect to the power supply voltage and the environmental temperature. Regardless of fluctuations
The digital conversion operation in the analog-digital conversion means can be optimized.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. It should be noted that the identification of various details in the following description or examples and examples of numerical values, character strings, and other symbols are merely references for clarifying the idea of the present invention, and may be used by all or a part of them. Obviously, the inventive idea is not limited. Also,
Well-known techniques, well-known procedures, well-known architectures, well-known circuit configurations, etc. (hereinafter, “well-known matters”) will not be described in detail, but this is also for the purpose of simplifying the explanation. It is not intended to exclude all or part of it. Such a well-known matter can be known to those skilled in the art at the time of filing the present invention, and is naturally included in the following description.

FIG. 1 is a conceptual configuration diagram of an optical system of a fingerprint authentication system 10 according to this embodiment. The fingerprint authentication system 10 shown in the figure is different from the fingerprint authentication system 1 in the related art (FIG. 10) described at the beginning, and is exemplified by a type in which components corresponding to the image reading device 2 and the fingerprint collation device 3 are integrated. However, it is not limited to this. It may be a separate type as in the prior art.

In FIG. 1, reference numeral 11 denotes a case, and a prism 12 is fixed so as to close an opening of a front end side slope 11a of the case 11. Further, a surface light source 13 that irradiates light to the prism 12 is fixed to the bottom surface 11b on the front end side of the case 11, and is further arranged inwardly of the prism 12 in the case 11 to provide a surface light source. Illuminated from 13 and the inclined surface (reading surface) 12a of the prism 12
A plurality of optical system components (first lens 14, diaphragm 15 and second lens 16) for forming an image of the light flux reflected inwardly,
Two as "imaging means" described in the gist of the invention, which is provided on the rear end side of the case 11 and receives the light guided through the optical system component at or near the imaging position and outputs the image signal Pa. A three-dimensional solid-state imaging device (for example, a CCD type imaging device, and abbreviated as “CCD” hereinafter) 17;
A ring-shaped guide member 18 arranged at an outer peripheral position (an inner peripheral position of the opening) on the inclined surface 12a of the prism 12,
A contact sensor 19 for detecting the contact of the finger Y with the guide member 18 and outputting a finger detection signal S _CONTACT is provided, and the operating temperature of the CCD 17 or the ambient environment temperature of the CCD 17 is detected to output a temperature signal S _TEMP . Output temperature sensor 2
0, battery 2 for supplying power to fingerprint authentication system 10
1 and a control unit 23 that controls each unit of the fingerprint authentication system 10.

Here, the prism 12 is made of transparent or translucent synthetic resin or glass that transmits light. In this case, as shown in FIG. 1, the side surface has an isosceles right triangle shape (that is, a right angle prism). ). In this prism 12, a part of the inclined surface 12a is exposed from the inside of the guide member 18 to the outer surface, and a part of the inclined surface 12a constitutes a reading surface 12a of the fingerprint of the finger Y. is there.

The surface light source 13 is composed of a light emitting element such as an LED, and is turned on or off by a control signal CONd output from the control section 23 to be in a light emitting state or a non-light emitting state.

In the figure, CONa is the CCD 17
Is a control signal (or a drive signal group) for controlling the image pickup operation of the control signal CONa.
It shall be generated by the control unit 23.

FIG. 2 is a conceptual block diagram of an electric signal system of the fingerprint authentication system 10 in this embodiment. In the example shown in the figure, the CCD 17, the contact sensor 19, the temperature sensor 20, and the surface light source 13 are integrated into the controller 23, but the invention is not limited to this. For example, the CDS 23c described below may be included in the configuration of the CCD 17.

In FIG. 2, the control unit 23 includes a constant power supply unit 2
3a, power supply voltage sensor 23b, correlated double sampling section (hereinafter "CDS") 23c, signal amplification section (hereinafter "AM").
P ") 23d, analog-digital converter (hereinafter referred to as" A "
D ") 23e, input interface 23f, electrically rewritable nonvolatile information storage unit (hereinafter referred to as" EEPRO ").
M ”) 23g, information processing unit (hereinafter“ CPU ”) 23h,
Read-only non-volatile information storage unit (hereinafter "ROM") 2
3i, a volatile information storage unit (hereinafter “RAM”) 23j, an output interface 23k, and the like, and the functions and operations of these units are as follows.

<Constant Power Supply Unit 23a> The voltage from the battery 21 (battery voltage) is converted into a constant voltage value, and the constant voltage is output to each unit of the control unit 23. Here, the battery voltage is generally DC 12V or DC 24V, while the voltage value required by each unit of the control unit 23 is a lower voltage (for example, DC 5V). Hereinafter, the constant voltage unit 23c converts the voltage from the battery 21 into DC5V and outputs it, and this output voltage (DC5V) is referred to as "power supply voltage Vdd".

<Power Supply Voltage Sensor 23b> The power supply voltage sensor 23b detects the power supply voltage (here, the power supply voltage Vdd) supplied to the fingerprint authentication system 10, and detects the power supply voltage Vd.
It outputs a voltage signal S _VOLT that is proportional to dd. A detailed description of the power supply voltage sensor 23b will be given later.

<CDS 23c> FIG. 3A shows the CCD 1
7 is an output signal waveform diagram of FIG. In this figure, T _R is C
The reset period of CD17, T _O is the first half period of charge accumulation in CCD 17 (also called floating period), T _S is CC
In the second half period of charge accumulation in D17, the signal level V _S in the second half period T _S of CCD charge accumulation is extracted as the image signal Pa. Here, since V _S includes reset noise of the output amplifier (floating diffusion amplifier) of the CCD 17 (KTC noise is also present but reset noise is dominant), S / N is improved. to signal that samples the potential level of the floating period T _O, the difference between the potential (V _S) of the sampled voltage and CCD charge storage latter period T _S, the true CCD output signal (image signal Pb) The operation is performed. This signal manipulation is called correlated double sampling.

<AMP23d> The AMP23d is the CDS
23c and AD23e, the reference potential (clamping potential) of the image signal Pb extracted from the CDS 23c.
Is increased or decreased according to the control signal CONb. Hereinafter, an image signal whose clamp potential is controlled will be referred to as an image signal Pc.

FIG. 3B is a block diagram of an example of the AMP 23d. In this figure, the AMP 23d is a resistor 23d.
_1 to 23d_3, capacitors 23d_4, 23d_
5, transistor 23d_6, and diode 23d
_7, the collector of the transistor 23d_6 is connected to the power supply voltage Vdd, the emitter of the transistor 23d_6 is connected to the ground potential via the resistor 23d_3, and the base of the transistor 23d_6 is connected to V via the resistor 23d_1.
The control signal CONb is applied to the base of the transistor 23d_6 via the resistor 23d_2 and the diode 23d_7, and the image signal Pb extracted from the CDS 23c is applied to the capacitor 23d_4. Image signal P from the emitter of the transistor 23d_6 to the base of the transistor 23d_6 via
It is configured to take out c.

In such a configuration, the image signal Pb extracted from the CDS 23c is capacitively coupled, that is,
Since it is added to the base of the transistor 23d_6 via the DC component blocking capacitor 23d_4, the resistance 23
Ignoring the presence of d_1, 23d_2, diode 23d_7 and capacitor 23d_5, transistor 23
The image signal Pb at the base of d_6 has an AC waveform that swings in the positive and negative directions with 0 V as the reference potential (FIG. 4).
See (a). However, the illustrated waveform is a sine wave for convenience. ).

Now, the resistor 23d_2 and the diode 23d
If only the presence of _7 is ignored, that is, the control signal C
When ONb is set to a predetermined potential and the diode 23d_7 is turned off, the reference potential is the capacitor 23d_7.
5 charging potential (that is, power supply voltage Vdd → resistor 23d
_1 → capacitor 23d_5 → charging potential generated by a closed circuit of the ground potential), and the voltage rises to approximately Vdd (see FIG. 4B).

When the control signal CONb is set to a negative potential in this state, the diode 23d_7 is turned on and the charging potential of the capacitor 23d_5 is discharged toward this negative potential, so that the negative potential of the control signal CONb is changed. The discharge time constant of the capacitor 23d_5 (resistor 23d
It is given by the product of the resistance value of d_2, the forward resistance value of the diode 23d_7 and the capacitance value of the capacitor 23d_5)
The reference potential can be lowered to a level corresponding to the negative potential by making the length sufficiently larger than the above.

That is, in FIG. 4A, the reference potential is 0V.
Waveform diagram of the image signal Pc when it is assumed to be equivalent, FIG.
[FIG. 6] is a waveform diagram of the image signal Pc when the reference potential is equivalent to Vdd. By changing the potential of the control signal CONb,
By switching between turning on and off the diode 23d_7, either one of the waveforms can be obtained.

By variably controlling the length of the negative potential of the control signal CONb, the waveform shown in FIG. 4A and the waveform shown in FIG. 4B can be continuously changed. it can. For example, the length of the negative potential is set to the capacitor 23d_5.
If the discharge time constant is about half, the above reference potential becomes 0
It can be V or more and Vdd or less. Figure 4 (c) shows
FIG. 9 is a waveform diagram (so-called PWM waveform) of the control signal CONb, in which the ratio of the length of the negative logic period L _{N and} the length of the positive logic period L _P of the control signal CONb is variably set to set the reference potential of the image signal Pc. Can be arbitrarily set between 0V and Vdd.

<AD23e> FIG. 5A shows the AD23e.
3 is a conceptual diagram of input / output characteristics of the. AD23e is intended for converting analog potential input (image signals Pc) of the digital voltage (image signal Pd of), the E input voltage range _L to E _H (E _L is the lowest potential, E _(H is the highest potential)
When the output voltage range it is an (highest potential corresponding to D _L is the lowest potential corresponding to E _L, D _H is E _H) D _L ~D _H.

These voltage ranges are so-called dynamic ranges, and potentials outside this range are not subject to normal digital conversion. Therefore, the image signal Pc input to the AD 23e must be within this dynamic range. That is, the lowest potential of the image signal Pc must be E _L or higher and the highest potential of the image signal Pc must be E _H or lower. This is because if the condition is not satisfied, the information of the white level or the black level of the image signal Pc is lost and a good fingerprint image cannot be obtained.

In particular, for example, for in-vehicle use,
When used in an environment where the temperature is often high, the above conditions may not be satisfied due to changes in the battery voltage and changes in the environmental temperature, which has been an obstacle to application to the in-vehicle fingerprint authentication system. In the present embodiment, in order to solve this inconvenience, a sensor (temperature sensor 20 or power supply voltage sensor 23b) for detecting a change in battery voltage or a change in environmental temperature is provided and detection from these sensors is provided. The operating point (reference potential: clamp potential) of the AMP 23d is adaptively controlled based on the signal.

<Input Interface 23f> The input interface 23f takes in signals from the temperature sensor 20, the power supply voltage sensor 23b, the contact sensor 19 and the AD 23e and outputs them to the CPU 23h.

<Temperature sensor 20 and power supply voltage sensor 23
b> FIG. 5B is an example configuration diagram of the temperature sensor 20, FIG.
(C) is an example configuration diagram of a power supply voltage sensor 23b,
Both are common in that the potential difference between the power supply voltage Vdd and the ground potential is taken out by resistance voltage division. That is, the temperature sensor 20 has a resistor 20 between Vdd and the ground potential.
a and 20b are connected in series and the temperature signal S
It is common that the _TEMP is taken out and the power supply voltage sensor 23b is also connected in series with the resistors 23b_1 and 23b_2 between Vdd and the ground potential and takes out the voltage signal S _VOLT from the connection point. The difference is that one of them is composed of an element having temperature dependence. Hereinafter, for convenience of explanation, it is assumed that the resistor 20a on the upper side in the drawing is an element having temperature dependence and that the resistance value linearly decreases as the temperature rises.

In such a configuration, the voltage signal S _VOLT
Changes in proportion to the fluctuation of the power supply voltage Vdd, and the temperature signal S _TEMP changes in proportion to the fluctuation of the power supply voltage Vdd and also in proportion to the fluctuation of the temperature. Although the temperature signal S _TEMP includes both the power supply fluctuation component and the temperature fluctuation component, the true temperature fluctuation component can be extracted by removing the power supply voltage fluctuation component given by the voltage signal S _VOLT from the temperature signal S _TEMP. it can. This removing operation is executed by a control program described later, but in the following description, for simplification, the temperature signal S _TEMP includes only a true temperature fluctuation component.

<EEPROM 23g> EEPROM 23
g is collation information for fingerprint collation, that is, in advance,
The fingerprint information (feature point information) of the person to be collated (hereinafter referred to as “the person”) read by using the fingerprint authentication system 10 or another fingerprint information reading system is held. The held fingerprint information may be for one person, or may be for all persons who may drive a vehicle equipped with the fingerprint authentication system 10.

<CPU 23h> The CPU 23h controls the overall operation of the fingerprint authentication system 10 according to a control program described later.

<ROM 23i> The ROM 23i stores and holds the above control program and also stores and holds look-up tables (V_Low, V_Mid, V_Hi) described later.

FIG. 6 is a conceptual diagram of the memory map of the ROM 23i, in which 23i_1 is a control program storage area and 2
3i_2 is a lookup table V_L for low power supply voltage
ow storage area, 23i_3 is a storage area for the medium power supply voltage lookup table V_Mid, and 23i_4 is a storage area for the high power supply voltage lookup table V_Hi. In addition, there are three types of power supply voltage (low, medium, high).
Although the lookup table corresponding to each of the above is taken as an example, it is needless to say that the lookup table is not limited to this, and for example, two or four or more types may be used.

<RAM23j> RAM23j is a CPU
It is used as a work area of 23h, the above control program is loaded into this RAM 23j, and the CPU 23
executed by h.

<Output Interface 23k> The output interface 23k outputs various control signals obtained as a result of execution of the control program by the CPU 23h, that is, a control signal CON for controlling the image pickup operation of the CCD 17.
a, a control signal CONb for controlling the reference potential in the AMP 23d, a sampling clock signal CONc for the AD 23e, a control signal CONd for ON / OFF controlling the surface light source 13, and the like.

Next, the operation will be described. FIG. 7 shows the ROM 2
Look-up table V_Low for low power supply voltage and look-up table V_ for medium power supply voltage stored in 3i
Mid and lookup table V for high power supply voltage
It is a figure which shows the example of _Hi. These three look-up tables (V_Low, V_Mid, V_Hi)
_Are selectively used according to the magnitude of the detection output (voltage signal S _VOLT ) of the power supply voltage sensor 23b. For example, when the magnitude of the voltage signal S _VOLT is within a predetermined low voltage range, the lookup table V for the low power supply voltage is used.
_Low is selected, or the magnitude of the voltage signal S _VOLT is within a predetermined medium voltage range, the lookup table V_Mid for the medium power supply voltage is selected, or the magnitude of the voltage signal S _VOLT is If it is within the predetermined high voltage range, the lookup table V for the high power supply voltage
_Hi is selected.

These three look-up tables (V_
Low, V_Mid, V_Hi) each have a correction value storage area divided into a plurality of temperature sections,
A correction value (or a control value) for controlling the reference potential of the AMP 23d is stored in these storage areas. The CPU 23h has three look-up tables (V_Low, V_Mid, V_Hi) according to the magnitude of the detection output (voltage signal S _VOLT ) of the power supply voltage sensor 23b.
_Is selected and the temperature category of the selection table is specified according to the magnitude of the detection output (temperature signal S _TEMP ) of the temperature sensor 20, and the correction value is looked up from the correction value storage area of the temperature category, The ratio between the negative logic period L _N and the positive logic period L _P of the control signal CONb is set according to the lookup value thus corrected.

Here, the lookup table (V
The temperature classification of _Low, V_Mid, V_Hi) is "-
"Less than 30 degrees", "-30 degrees to less than -20 degrees", "-
20 degrees or more and less than -10 degrees "," -10 degrees or more and less than 0 degrees "," 0 degrees or more and less than 10 degrees "," 10 degrees or more to 20 degrees "
"Less than", "20 degrees or more and less than 30 degrees", "30 degrees or more and less than 40 degrees", "40 degrees or more and less than 50 degrees", "50
There are 11 divisions in increments of 10 degrees such as "greater than or equal to 60 degrees and less than 60 degrees" and "more than 60 degrees", but this is an example. It may be finely chopped or roughly 10 degrees or more.

In the temperature category shown in the example, the room temperature of the installation environment (generally, the interior of the vehicle) of the fingerprint authentication system 10 for in-vehicle use can be said to be approximately "20 degrees to less than 30 degrees". Hereinafter, the temperature in this temperature range is referred to as "normal temperature". Further, the power supply voltage Vdd shows the highest voltage (that is, the high voltage range) when the battery is in a fully charged state, the internal voltage drop is small, and the load power consumption is zero, and conversely, the battery is almost discharged. It shows the lowest voltage (that is, low voltage range) when the load power consumption is large in the state or when the internal voltage drop is large or the air conditioner etc. is turned on. The voltage between the range and the low voltage range (ie, the medium voltage range) is shown. Therefore, hereinafter, the power supply voltage Vdd when it is in the middle voltage range is referred to as a “normal voltage”.

When the voltage signal S _VOLT corresponds to "normal voltage" and the temperature signal S _TEMP corresponds to "normal temperature", the temperature classification "20 degrees or more ... Correction value "6" from less than 30 degrees
5 "is taken out. The meaning of the correction value" 65 "is, for example, to set the ratio between the negative logic period L _N and the positive logic period L _P of the control signal CONb to" 65: 1 ".
Charging period “1” of the capacitor 23d_5 of the AMP 23d
On the other hand, the ratio of the discharge period is "65".

On the other hand, the lookup table V_Mid
For example, the correction value for the temperature category "60 degrees or more" is "5.
0 ", which is similar to the above, in that the ratio of the discharge period to the charge period" 1 "of the capacitor 23d_5 of the AMP 23d is" 50 ".

Comparing the two, the proportion of the discharge period in the case of the temperature classification "60 degrees or more" is small. As described above, the capacitor 23d_ of the AMP 23d
The potential of 5 rises as the negative logic period L _N of the control signal CONb becomes shorter (or its ratio becomes smaller) (approaching the level of FIG. 4B), so that the look-up table V_Mid is eventually used. For example, the higher the temperature is, the higher the reference potential (clamp potential) of the AMP 23d can be increased.

This also applies to other lookup tables (V_Low, V_Hi). This is because each of them stores the correction value that becomes smaller as the temperature becomes higher. The correction values stored in the three look-up tables (V_Low, V_Mid, V_Hi) are merely for convenience of description. In essence, various power supply voltage values and temperatures are combined to experimentally or empirically find a correction value for obtaining an appropriate reference potential of the AMP 23d for each combination, and the correction values are looked up in a look-up table ( V_Low, V_Mi
d, V_Hi) may be written in each correction value storage area.

Further, in the above description, the correction value for each preset temperature section is taken out, but the present invention is not limited to this mode. For example, a correction value for each of the representative temperature points is stored, and a correction value that does not correspond to the representative temperature point is obtained by linear interpolation calculation using the correction values of a plurality of representative temperature points close to the temperature. May be.

FIG. 8 is an operation flowchart of the fingerprint authentication system in this embodiment. In this flowchart, after performing clamp control (step S11; clamp control will be described later) that is a process peculiar to this embodiment, a background image is captured (step S12). This is repeated endlessly until the result of the device detection (step S13) becomes YES.
The background image is a background image before the fingerprint is read.

When the fingerprint authentication system 10 is mounted on a vehicle (that is, when it is mounted on a vehicle),
As shown in FIG. 1, a legitimate driver (driver who has registered fingerprint information in the fingerprint authentication system, that is, “the person”)
When the finger Y is placed on the inclined surface (reading surface) 12a of the prism 12, the contact sensor 19 outputs a finger detection signal S _CONTACT , and the result of the finger placement detection (step S13) is YE.
It becomes S.

When the finger placement is detected, the clamp control, which is a process peculiar to the present embodiment, is performed again (step S14; the clamp control will be described later), and a fingerprint image is taken (step S15). After that, remove the background image component taken earlier from this fingerprint image,
Obtain a pure fingerprint image that does not include a background image (step S
16). Then, information on the characteristic points (end points, branch points, etc.) of the fingerprint is extracted from the fingerprint image (step S17), and E
When it is compared with the collation information stored in the EPROM 23g and the similarity is found at a certain ratio or more, the fingerprint is determined to be the fingerprint of the person (step S18), and the collation result is, for example, an engine starting device of the vehicle. (Step S19).

FIG. 9 is a flowchart of the clamp control (step 11 and step S14) which is a process peculiar to this embodiment. In this clamp control, first, the detection output (voltage signal S _VOLT ) of the power supply voltage sensor 23b and the detection output (temperature signal S _TEMP ) of the temperature sensor 20 are read (steps S21 and S22), and then the voltage signal S _{One of} the three look-up tables (V_Low, V_Mid, V_Hi) is selected according to the size of _VOLT , and the temperature division of the selected look-up table is selected according to the size of the temperature signal S _TEMP. The correction value (control value) stored in the temperature category is taken out (step S23). Then, the ratio of the negative logic period L _N and the positive logic period L _P of the control signal CONb is set by using the extracted correction value, so that the AMP 23d
The magnitude of the reference potential (clamp potential) is variably set according to the power supply voltage and the temperature value at that time.

Therefore, according to this clamp control,
Depending on the value of the power supply voltage and the temperature at that time, the AMP 23d
Since the size of the reference potential (clamping potential) is adaptively variably set, when used in a harsh environment such as an in-vehicle application, for example, (1) the light amount of the surface light source 13 is “environmental temperature” or “battery”. Power supply voltage ", or (2) the brightness level of the image signal output from the CCD 17 is" environmental temperature "or" battery power supply voltage ".
Change under the influence of fluctuations in, or (3) A
Even when the reference potential (clamping potential) of D23e changes under the influence of "environmental temperature" or "battery power supply voltage", those influences are adaptively controlled by the reference potential (clamping potential) of AD23e. Can be eliminated or suppressed. As a result, it is possible to improve the image quality of the fingerprint image, and thereby improve the certainty of the personal authentication, which is a special effect not found in the related art at the beginning.

In this embodiment, the temperature sensor 20
Is arranged in the immediate vicinity of the CCD 17 to detect the ambient temperature of the CCD 17, but the invention is not limited to this. The point is that the operating temperature of the CCD 17 itself or the ambient temperature can be detected, and for example, an internal mounting type of the CCD 17 or a substrate embedded type temperature sensor of the CCD 17 may be used. Alternatively, the temperature correlation value may be detected using another physical quantity (for example, the output voltage of the redundant photoelectric conversion element of the CCD 17) that changes in correlation with the operating temperature of the CCD 17 itself or the ambient environment temperature. .

[0064]

According to the present invention, the fingerprint image signal photographed by the image pickup means is corrected on the basis of the fluctuation of the power supply voltage and the fluctuation of the environmental temperature under the on-vehicle environment.
The influence of these fluctuation factors can be suppressed, and the accuracy and quality of image reading can be improved. As a result, it is possible to realize a fingerprint authentication system capable of obtaining sufficient personal authentication performance even in an in-vehicle environment.

Further, according to a more preferable configuration of the present invention, the correction value output means uses the power supply voltage value and the temperature value as input parameters, and the analog-to-digital conversion means corresponding to the input parameters. Since it has a correspondence table (for example, a look-up table) for outputting the correction value of the clamp potential of the fingerprint image signal with respect to, the optimum correction corresponding to various combinations of the power supply voltage and the environmental temperature is performed in advance. By experimentally or empirically finding the value and storing it in a lookup table, you can use it without using complicated model expressions.
It is possible to easily and quickly generate and output the required correction value.

Further, according to a more preferable configuration of the present invention, the correction means is an amplifier circuit inserted in the preceding stage of the analog-digital conversion means, and the clamp potential of the fingerprint image signal is adjusted according to the correction value. Since the clamp potential of the fingerprint image signal input to the analog-to-digital conversion means is adaptively adjusted with respect to the power supply voltage and the environmental temperature, it is possible to prevent the fluctuation of the power supply voltage and the environmental temperature. Therefore, the digital conversion operation in the analog-digital conversion means can be optimized.

[Brief description of drawings]

FIG. 1 is a conceptual configuration diagram of an optical system of a fingerprint authentication system 10 according to the present embodiment.

FIG. 2 is a conceptual configuration diagram of an electric signal system of the fingerprint authentication system 10 according to the present embodiment.

FIG. 3 is a waveform diagram of the output signal of the CCD 17 and the AMP 23d.
It is an example block diagram.

FIG. 4 is an image signal Pc when the reference potential is 0V.
5 is a waveform chart of the image signal Pc and a waveform chart of the control signal CONb when the reference potential is equivalent to Vdd.

FIG. 5 is a conceptual diagram of input / output characteristics of AD23e, temperature sensor 2
0 is an example configuration diagram and a power supply voltage sensor 23b is an example configuration diagram.

FIG. 6 is a conceptual diagram of a memory map of a ROM 23i.

FIG. 7 is a diagram showing an actual example of a lookup table stored in a ROM 23i.

FIG. 8 is a diagram showing an operation flowchart of the fingerprint authentication system in the present embodiment.

FIG. 9 is a diagram showing a flowchart of clamp control, which is a process peculiar to this embodiment.

FIG. 10 is a simplified configuration diagram of a conventional fingerprint authentication system 1.

[Explanation of symbols]

V_Low lookup table (correspondence table) V_Mid lookup table (correspondence table) V_Hi lookup table (correspondence table) 10 Fingerprint authentication system 17 CCD (imaging means) 20 Temperature sensor (temperature detection means) 23b Power supply voltage sensor (power supply voltage detection means) 23d AMP (correction means, amplification circuit) 23e AD (Analog to Digital Converter) 23h CPU (correction value output means)

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Seiji Ogura             1726 Naruto, Kitaharayama-cho, Owariasahi-shi             City Misato 1-1109 F-term (reference) 4C038 FF01 FF05 FG01                 5B047 AA25 AB02 BA02 BB04 BC04                       BC11 BC14 CB02 CB03 DB01                       DB06

Claims (3)

[Claims] 1. A fingerprint authentication system comprising an image pickup means for picking up a fingerprint image and generating and outputting the fingerprint image signal, and an analog-digital converting means for converting the fingerprint image signal into a digital signal, wherein the fingerprint A power supply voltage detection means for detecting a power supply voltage supplied to the authentication system, a temperature detection means for detecting an operating temperature of the image pickup means itself or an ambient environment temperature, and a power supply voltage value detected by the power supply voltage detection means. A correction value output unit that generates and outputs a correction value for the fingerprint image signal based on the temperature value detected by the temperature detection unit; and a correction unit that corrects the fingerprint image signal using the correction value. A fingerprint authentication system characterized by. 2. The correction value output means uses the power supply voltage value and the temperature value as input parameters, and corrects the clamp potential of the fingerprint image signal to the analog-digital conversion means in accordance with the input parameters. The fingerprint authentication system according to claim 1, further comprising a correspondence table that outputs a value. 3. The correction means is an amplifier circuit inserted in the preceding stage of the analog-digital conversion means, and adjusts the clamp potential of the fingerprint image signal according to the correction value. The fingerprint authentication system according to claim 2.