JP2747489B2 - Fingerprint sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Overview] Regarding a fingerprint sensor used as an identification means when entering a computer room or using a terminal, a finger is brought into contact with an input surface for the purpose of detecting a living body in a short time. System fingerprint sensor,
A speckle light detecting means including an illuminating means for irradiating the side surface of the finger in contact with the input surface with a laser diode or the like, a light receiving means arranged at a position facing the laser diode or below the input surface, and a level detecting circuit And a biological signal detecting means comprising a speckle detecting circuit, so that it is possible to identify whether or not the finger touching the input surface is a living body.

[Industrial applications]

The present invention relates to a fingerprint sensor used as personal identification means when entering a computer room or using a terminal according to the present invention.

In recent years, with the introduction of computers into a wide range of social systems, stakeholders have been interested in system security. ID cards and passwords that have been used as a means of verifying identity when entering a computer room or using a terminal cannot be distinguished from others when used by another person, and questions are raised in terms of ensuring security. Has been raised.

Fingerprints, on the other hand, are considered to be the most powerful means of identity verification because they have two major characteristics: "everyone is unidentified" and "lifelong invariant". Is being done.

[Conventional technology]

FIG. 5 is a diagram showing an example of a conventional fingerprint sensor. This is configured by providing a hologram 2 on a transparent flat plate 1 and separately providing an illumination laser light source 3 and an image pickup device 4. When the finger 5 is brought into contact with the transparent flat plate 1, the reflected light at the convex portion of the fingerprint becomes scattered light and travels in all directions in the transparent flat plate 1, whereas the scattered light reflected at the concave portion of the fingerprint contains air. Therefore, it can only advance within a certain incident angle range. Utilizing this principle, light 6 reflected from the convex portion of the fingerprint is propagated in the transparent flat plate 1 under the condition of total reflection, this light is guided outside by the hologram 2, and the fingerprint is detected by the image pickup device 4. I have.

However, in such a fingerprint sensor, contrast is obtained by utilizing the difference in the amount of reflected light due to contact / non-contact between the skin and the glass on the input surface, so a fingerprint replica made of an elastic material such as silicon rubber is used. When a finger is pressed against the input surface, a fingerprint image similar to that obtained by pressing a finger of a living body is obtained. Therefore, a fingerprint sensor having a living body detection function has been developed to ensure security.

As a conventional living body detection method, when a fingertip is pressed against glass on an input surface to optically capture an image, a method of judging a temporal change of a sensor output by software is used. That is, as shown in FIG. 6, sweating from the fingertip improves the optical contact between the convex portion of the fingerprint and the glass, and the sensor output increases with time to determine whether the subject is a living body. is there.

[Problems to be solved by the invention]

In the above-mentioned biometric detection method that determines the temporal change of the sensor output by software, it is necessary to repeat software routines such as image capture, A / D conversion, and comparison with the previous output. Because you can not enter
There was a problem that the required time was long.

An object of the present invention is to provide a fingerprint sensor that can perform living body detection in a short time.

[Means for Solving the Problems] FIG. 1 is a diagram for explaining the principle of the present invention.

Generally, when a rough surface is illuminated with coherent light such as a laser, reflected lights interfere with each other in front of the rough surface, and noise light called "speckle" is generated. At this time, it is known that if the rough surface is slightly vibrated, the interference condition is broken and the speckle disappears. FIG. 1A shows a case where a replica 10 of a fingertip imitated with silicon rubber or the like is placed on the input surface 12 instead of the finger. In this case, a laser diode
The laser light that has entered the replica 10 from 13 diffuses inside the replica, and enters the inside of the glass 14 from the ridge contacting the input surface. At this time, since the coherency of the laser beam is not lost inside the replica, a fingerprint image including speckles is observed in the imaging device. In contrast, the first
FIG. 2B shows a case where the finger 11 of the living body is placed on the input surface 12.
In this case, in the finger 11 of the living body, the capillaries 15 are distributed all the way to the end of the fingertip, and there is a constant blood flow. Therefore, the laser beam incident from the side surface of the finger 11 is disturbed in the diffusion direction mainly by the movement of hemoglobin, and speckles on the input surface disappear.

[Action]

When detecting speckles from a finger touching the input surface by the speckle detecting means, detecting that it is not a living body by the biological signal detecting means, and not detecting speckles from the finger touching the input surface, The biological signal detecting means detects that the object is a living body.

〔Example〕

This embodiment includes a living body detection optical system and speckle detection means.

FIGS. 2A and 2B are diagrams showing two examples of a living body detection optical system. 1A shows a laser diode 13 arranged near the side of a finger 11 to be detected, and a condenser lens 16 and a light receiving element 17 arranged below an input surface 12. FIG. FIG. 2 (b) shows a laser diode 13 disposed on one side of a finger 11 on an input surface 12 and a condenser lens 16 and a light receiving element 17 disposed on the other side. The presence or absence of light can be detected.

Although the above example is an example applied to a holographic fingerprint sensor, it can also be applied to a prism type fingerprint sensor. When another optical system is used, it is necessary to change the algorithm of the speckle detecting means as described later.

FIG. 3 is a block diagram showing speckle detecting means according to the embodiment of the present invention. The speckle detecting means 20 includes a level detecting circuit 21 and a speckle detecting circuit 22. The level detection circuit 21 includes an amplifier 23 and an analog comparator 24. The analog comparator 24 compares a value obtained by amplifying the output signal of the light receiving element 17 with the amplifier 23 with a threshold value. When it is obtained, a "finger detection signal" is output. On the other hand, the speckle detection circuit 22 includes a band pass filter 25, an analog comparator 26, an AND gate 27, a digital counter 28, a one-shot multi 29, a digital comparator 30, and the like. The output signal of the light receiving element 17 passes only a signal (speckle) of a predetermined frequency band by the band-pass filter 25, and is then compared with a threshold by the analog comparator 26, and a speckle signal having a level higher than the threshold is sent to the AND gate 27. Sent. On the other hand, the finger detection signal from the level detection circuit 21 is input to the one-shot multi 29. As shown in the timing chart of FIG. 4, the one-shot multi 29 opens the AND gate 27 for a fixed time after the finger touches the input surface. During this time, the digital counter 28 counts the number of speckles that have passed through the AND gate 27, and the digital comparator 30 compares the count with a threshold value. If so, it is determined that the subject is a living body, and a living body detection signal is output.

As described above, in the holographic fingerprint sensor, the sensor output is low until the finger touches the input surface. Therefore, when the speckle detection signal is output from the speckle detection circuit 22 after the level detection circuit 21 detects the contact of the finger, it is determined that the replica has been pressed. When a fingerprint sensor optical system of another system is used, the output algorithm of the "finger detection signal" of the level detection circuit may be slightly changed.

In this embodiment, the light receiving element for speckle light is arranged independently of the image sensor for fingerprint image. However, the same object and problem can be obtained even if the signal component due to speckle light is separated from the image sensor output for fingerprint image. Needless to say, it can be achieved.

〔The invention's effect〕

As described above, according to the present invention, living body detection can be performed independently of the movement of the CPU that controls the matching hardware, and the amount of control software and the matching time can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the principle of the present invention, FIG. 2 is a diagram illustrating a living body detection optical system according to an embodiment of the present invention, FIG. 3 is a block diagram illustrating speckle detecting means according to the embodiment of the present invention, FIG. 5 is a timing chart of a speckle detection circuit, FIG. 5 is a diagram showing a conventional fingerprint sensor, and FIG. 6 is a diagram showing a change in the output of the fingerprint sensor due to sweating of a fingertip. In the figure, 10 is a replica, 11 is a living finger, 12 is an input surface, 13 is a laser diode, 14 is glass, and 15 is a blood vessel.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Fumio Yamagishi 1015 Uedanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Prefecture Inside Fujitsu Limited (72) Inventor Hiroyuki Ikeda 1015 Kamikodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Fujitsu Limited ( 56) References JP-A-1-281583 (JP, A)

Claims (1)

(57) [Claims] 1. A fingerprint sensor in which a finger is brought into contact with an input surface, wherein illumination means for irradiating a side surface of the finger (11) brought into contact with the input surface (12) with a laser diode (13); 13) light emitted from 13) is reflected in front of the input surface (12), and a plurality of reflected lights interfere with each other to detect speckle light generated as noise. Alternatively, a speckle light detecting means including light receiving means disposed below the input surface (12), and a level detecting circuit (21) for outputting a finger detection signal when an output signal of the light receiving means becomes a certain value or more. And a biological signal detecting means comprising a speckle detecting circuit (22) for detecting the number of speckles within a predetermined time, and discriminates whether or not the finger touching the input surface (12) is a living body. Specially made that possible Fingerprint sensor to be.