JPH025190A - Finger print sensor - Google Patents

Abstract

PURPOSE:To rapidly inspect an organism by providing a finger print sensor with an lighting means, a speckle photodetecting means and an organism signal detecting means consisting of a level detecting circuit and a speckle detecting circuit so that a finger coming in contact with an input face is an organism or not can be identified. CONSTITUTION:A laser beam made incident from a laser diode 13 into a replica 10 is diffused in the replica and made incident form a projected line part in contact with the input face into a glass 14. Since the coherence of the laser beam is not lost in the replica, a finger print image including a speckle can be observed by an image pickup element. On the contrary, capillaries 15 are distributed in an organic finger 11 up to the terminal of the finger and blood always flows into the capillaries 15, so that the laser beam made incident from the side of the finger 11 is disturbed at its diffusion direction by the movement of hemoglobin and the speckle on the input face disappears. Consequently, an organism can be inspected independently of the movement of a CPU for controlling a collating hardware, the number of control softwares can be reduced and the collating time can be shortened.

Description

[Detailed Description of the Invention] [Summary] Regarding fingerprint sensors, which are used as a means of identifying individuals when entering a computer room or using a terminal, the purpose of this invention is to detect a living body in a short time by touching the input surface with a finger. In a type of fingerprint sensor, speckle light consists of an illumination means that illuminates the side surface of the finger that is in contact with the input surface using a laser diode, etc., and a light receiving means that is placed at a position facing the laser diode or below the input surface. The device includes a detection means and a biological signal detection means consisting of a level detection circuit and a speckle detection circuit, and is configured to be able to identify whether or not a finger touching the input surface is a living body.

[Industrial Application Field] The present invention relates to a fingerprint sensor used as an identification means when entering a computer room or using a terminal.

In recent years, as computers have been introduced into a wide range of social systems, system security has become a focus of interest among those concerned. ID cards and passwords, which have been used until now as a means of verifying identity when entering a computer room or using a terminal, are questionable from a security perspective because if someone else uses them, they cannot be distinguished from the user. It has been raised.

Fingerprints, on the other hand, are "the same for everyone" and remain unchanged throughout life.
Because of these three major characteristics, it is considered the most powerful means of identity verification, and much research and development is being conducted on simple personal verification systems using fingerprints.

[Conventional technology]

FIG. 5 is a diagram showing an example of a conventional fingerprint sensor. This is constructed by providing a hologram 2 on a transparent flat plate 1, and separately providing an illumination laser beam #3 and a side image element 4. When the finger 5 is brought into contact with the transparent flat plate 1, the light reflected from the convex portions of the fingerprint becomes scattered light and travels in all directions inside the transparent flat plate 1, whereas the scattered light reflected from the concave portions of the fingerprint is caused by air. Therefore, it can only advance within a certain range of incident angles. Utilizing this principle, the light 6 reflected from the convex portion of the fingerprint is propagated through the transparent flat plate 1 under total internal reflection conditions, this light is guided to the outside by the hologram 2, and the fingerprint is detected by the image sensor 4. There is.

However, such fingerprint sensors obtain contrast 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 replica of a fingerprint made from an elastic material such as silicone rubber is used. If a fingerprint sensor is pressed against a surface manually, a fingerprint image similar to that of a living body is obtained, which is a drawback.For this reason, fingerprint sensors are equipped with a living body detection function to ensure security. A new model is being developed.

A conventional living body detection method uses software to determine temporal changes in sensor output when an image is optically captured by pressing a fingertip against a glass input surface. That is, as shown in Figure 6, sweating from the fingertips causes
The optical contact between the convex part of the fingerprint and the glass improves, and the sensor output increases over time to determine whether the fingerprint is a living body or not.

[Problem H to be solved by the invention] In the above-mentioned living body detection method that uses software to determine temporal changes in sensor output, it is necessary to repeat software routines such as image capture, A/D conversion, and comparison with the previous output. During this time, the CPU cannot enter into the fingerprint matching process, resulting in a problem that the required time becomes longer.

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

[Means to solve the problem]

FIG. 1 is a diagram for explaining the present invention in detail.

Generally, when a rough surface is illuminated with coherent light such as a laser, the reflected light interferes with each other in front of the rough surface, generating noise light called speckle.

It is known that if the rough surface is slightly vibrated at this time, the interference conditions will collapse and the speckles will disappear.

FIG. 1(a) shows a case where a replica IO of a fingertip made of silicone rubber or the like is placed on the human power surface 12 instead of a finger. In this case, from the laser diode 13 to the replica 10
The laser light incident on the replica is diffused inside the replica and enters the inside of the glass 14 from the ridge portion that came into contact with the manual surface. At this time, since the coherency of the laser light is not lost inside the replica, a fingerprint image containing speckles is observed on the imaging device. On the other hand, FIG. 1(b) shows a case where a living body's finger 11 is placed on the human force surface 12.

In this case, in the finger 11 of a living body, capillaries 15 are distributed all the way to the end of the fingertip, and there is a constant flow of blood.

Therefore, the direction of diffusion of the laser light incident from the side surface of the finger 11 is disturbed mainly by the movement of hemoglobin, so that speckles on the input surface disappear.

[For production]

If the speckle detection means detects speckles from a finger that has touched the input surface, the biological signal detection means detects that the finger is not a living body, and if no speckles are detected from the finger that has touched the input surface, The biological signal detection means detects that it is a living body.

[Example] This example consists of a living body detection optical system and speckle detection means.

FIGS. 2(a) and 2(b) are diagrams showing two examples of living body detection optical systems. (a) In the case shown in the figure, a laser diode 13 is placed near the side of the finger 11 to be detected, and a condensing lens 16
And a light receiving element 17 is arranged below the input surface 12. Also, what is shown in figure (b) is the finger 1 on the human force surface 12.
1, a laser diode 13 is placed on one side, and a condensing lens 16 and a light-receiving element 17 are placed on the other side.The light-receiving element 17 can detect the presence or absence of speckle light in both cases.

Note that although the above example is an example applied to a holographic fingerprint sensor, it can also be applied to a prism type fingerprint sensor. Furthermore, when using another optical system, it is necessary to change the algorithm of the speckle detection means as described later.

FIG. 3 is a block diagram showing speckle detection means according to an embodiment of the present invention, and the speckle detection means 20 includes a level detection circuit 21 and a speckle detection circuit 22. The level detection circuit 21 is composed of an amplifier 23 and an analog comparator 24, and compares the output signal of the light receiving element 17 with the dark value, and outputs an "r finger detection signal" when an output of a certain value or more is obtained. On the other hand, the speckle detection circuit 22 includes a bandpass filter 25, an analog comparator 2G,
It is composed of 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 is then connected to an AND gate 27 via a band pass filter 25 and an analog comparator 26. The finger detection signal is also connected to the one-shot multi 29, which opens the gate for a certain period of time after the finger touches the input surface, as shown in the timing chart of FIG. If the number of speckle pulses that have passed through the gate during this period is greater than or equal to a certain value, it is determined that the replica has made contact, and if the number of speckle pulses is less than or equal to a certain value, it is determined that there is a living body and a living body detection signal is output.

In this way, in the holographic fingerprint sensor, the sensor output is low until the finger touches the input surface.

After the level detection circuit 21 detects the finger contact,
When a speckle detection signal is output from the speckle detection circuit 22, it is determined that the replica has been pressed. Note that when a fingerprint sensor optical system of another type is used, a slight change may be made to the output algorithm of the "finger detection signal" of the level detection circuit.

Furthermore, in this embodiment, the speckle light receiving element is arranged independently from the fingerprint image bottle imaging element, but the same purpose can be achieved by separating the speckle light signal component from the fingerprint image image sensor output. Needless to say, it is important to accomplish the task.

(Effects of the Invention) As explained above, according to the present invention, it is possible to perform living body detection independently of the movement of the CPU that controls the verification hardware, reducing the amount of control software and shortening the verification time. It becomes possible.

[Brief explanation of the drawing]

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

Claims (1)

[Scope of Claims] 1. In a fingerprint sensor of the type in which a finger is brought into contact with an input surface, illumination means illuminates the side surface of the finger (11) in contact with the input surface (12) using a laser diode (13) or the like; speckle light detection means consisting of a light receiving means disposed at a position facing the laser diode (13) or below the input surface (12); a level detection circuit (21); and a speckle detection circuit (22).
1. A fingerprint sensor, comprising: a biological signal detecting means, and capable of identifying whether or not a finger in contact with an input surface (12) is a living body.