Image analysis – Applications – Personnel identification
Reexamination Certificate
2000-10-16
2004-08-17
Bali, Vikkram (Department: 2623)
Image analysis
Applications
Personnel identification
Reexamination Certificate
active
06778686
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to capacitive sensing of topological variations in the structure of an object. The invention particularly relates to a sensing device sensing topological variations in the structure of a finger or a fingertip, and to a so-called fingerprint recognition system.
STATE OF THE ART
Various sensing devices, particularly devices intended for sensing topological variations in the structure of a finger or a fingertip are known, which are based on capacitive sensing. One capacitive sensing device is known from U.S. Pat. No. 5,325,442. This device comprises an array of sensor elements which are connected to a drive circuit. Each sensor element comprises a sense electrode, and the array of sense electrodes is covered by a dielectric material defining a sensing surface. Each sensor element includes a switching device which is connected to its sense electrode which is actively addressable by the drive circuit controlling the operation of the switching device. In this manner, a predetermined potential can be applied to the sense electrode. The sensing device still further includes a sensing circuit for sensing a capacitance produced by individual finger surface portions in combination with respective sense electrodes when a finger is placed over the sensing surface. Active addressing of the sensing elements is enabled through the switching devices in each sensing element, which is intended to simplify the driving of the array. It is an object of the invention described in U.S. Pat. No. 5,325,442 to reduce the number of connections and the number of addressing conductors, as compared to other devices. This device is based on reflective sensing.
It could be said that a drawback of the device of U.S. Pat. No. 5,325,442 is that it offers a relatively low sensitivity, in that only one sensor element at a time can be used for sensing. An additional drawback of this device is that since one and the same element is used for transmitting and sensing, there is a risk that the element, when transmitting, will influence the element when sensing, in an undesired manner, by means of, for example, parasitic capacitances. Another problem with this device might be that sweat remaining on the sensor surface could influence the sensing.
SE-C448 408 also shows a capacitive sensing device which comprises a number of sensor elements arranged in a two-dimensional matrix. The object of the invention, as disclosed in said document, is to provide a device enabling a faster sensing and a device reducing the risk of the sensed pattern being influenced by the object, i.e. the finger, moving during the sensing operation. This device is also based on reflective sensing principles.
Still another sensing device is disclosed in EP-A-0 791 899. This device is based on capacitive sensing using direct sensing principles.
However, all sensing devices which are known so far suffer from drawbacks as far as the sensitivity is concerned, i.e. a higher sensitivity is sometimes needed, and furthermore, the sensor area, which particularly contains silicon, which is expensive, is not used as efficiently as would be desired. Furthermore, known sensing devices suffer from the drawback of being inflexible in use.
SUMMARY OF THE INVENTION
What is needed is therefore a sensing device which can be given the required sensitivity, which is efficient, and which is cost-efficient from a fabrication point of view. A sensing device is also needed which can be made small and still be highly efficient. Particularly, a sensing device for sensing topological variations in the structure of a finger or a fingertip is needed which meets the above-mentioned requirements, as well as a fingertip pattern or a fingerprint recognition device which here means a device comparing stored information about the variations in the topological structure of a finger with the corresponding information of a finger of a user wanting access to something.
In addition, what is needed is a sensing device with increased sensitivity as compared to prior art, with the possibility of adaptively controlling the sensitivity of the device from case to case. Also, in the case of a device with transmitting elements and sensing elements, what is needed is a sensing device in which the sensing elements can be shielded or insulated from the transmitting elements.
A method is also needed through which the topological variations in the structure of an object can be detected in an appropriate way, with the desired sensitivity and also in an easy and cost-efficient manner.
Therefore a capacitive sensing device is provided which is intended for sensing topological variations in the structure of an object. One example of such an object is a finger used in finger(tip) pattern recognition systems etc. to establish whether a user should be given access to something or not. Particular implementations will be described below. The sensing device comprises a sensing surface for receiving an object adjacent thereto and a number of sensor elements which are arranged in two dimensions in a matrix or in an array. The sensing device comprises controlling means for providing control signals to the sensor elements. At least a number of the sensor elements can be controlled or brought to have or to assume one of at least two different functionalities, and the actual functionality of a sensor element is controlled or determined by said control signals. Any of said at least two functionalities can be assumed by any one of the controllable sensor elements, and any other of said at least two functionalities can be assumed by any one of the other controllable sensor elements.
In a particular embodiment, any of said at least two functionalities can be assumed by any one of the controllable sensor elements, and any other of said at least two functionalities can simultaneously be assumed by any one of the other controllable sensor elements.
In addition, in one embodiment, any of said at least two functionalities can be assumed by any number of said controllable sensor elements, and any other of said at least two functionalities can be assumed by any number of the remaining controllable sensor elements.
The present invention also enables any of said at least two functionalities to be able to be assumed by any number of said controllable sensor elements, and any other of said at least two functionalities can simultaneously be assumed by any number of the remaining controllable sensor elements.
The functionalities available for the at least a number of controllable sensor elements which can be brought to take one of at least two different functionalities comprise a driving functionality in which a sensor element acts as a transmitting element and a sensing functionality in which a sensor element acts as a receiving element. This means that the sensor elements, or at least a number of the sensor elements, are bi-directional, which means that they can be selected to act either as a transmitter or as a receiver.
Due to the flexibility of the sensing device of the present invention, the sensitivity of the device can be varied adaptively from case to case, since the number of transmitting elements as well as the number of sensing elements can be varied from case to case. Additionally, since any element can be used as transmitting element, with any of the other elements being used as the corresponding sensing element, the distance between transmitter and receiver (sensor) can be varied at will, thus raising the level of isolation between transmitter and receiver. In addition, since the distance between the transmitting element(s) and the receiving element(s) can be chosen freely, the problem of remaining sweat on the sensor surface can be obviated.
In a further embodiment, at least a number of the controllable sensor elements can be controlled to assume a third functionality. Preferably, all sensor elements are operable in all said three functionalities and can thus be controlled to have any of at least three different functionalities.
Suitably, said third functionality is
Hestnes Njård
Riedijk Frank Robert
Bali Vikkram
Birch & Stewart Kolasch & Birch, LLP
Fingerprint Cards AB
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