JP2004355367A - Fingerprint detection circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fingerprint detection circuit that can be powered only when a finger is placed on a fingerprint sensor. <P>SOLUTION: The fingerprint detection circuit comprises a two-dimensional array sensor and a detection circuit. The fingerprint detection circuit includes a scanning means for scanning a part of the outputs of the two-dimensional array sensor; a counting means for counting the number of pulses outputted from the scanning means; a determining means for outputting a determination signal when the count of pulses by the counting means exceeds a predetermined threshold; and a power supply control means for turning on the power supply to the detection circuit when the determination signal is outputted. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a fingerprint detection circuit for detecting a fingerprint.
[0002]
[Prior art]
As a conventional fingerprint collation device, a fingerprint detection element that captures fingerprint information of a finger as image information when a subject's finger is touched, a control unit that controls turning on and off an operation power supply of the fingerprint detection element, The control means starts the operation power supply of the fingerprint detection element immediately before the finger comes into contact with the fingerprint detection element, and shuts off the operation power supply immediately after the end of the fingerprint information capture, thereby saving power. The following is known (for example, Patent Document 1).
[0003]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2001-056582
[Problems to be solved by the invention]
However, in the fingerprint matching device disclosed in Patent Document 1, a leaf spring is installed around the fingerprint sensor, and when the finger is placed on the fingerprint sensor, the finger touches the leaf spring, and the leaf spring is used. In addition, since the power supply is controlled, even if something other than a finger touches the leaf spring, the power is turned on, which is not preferable in terms of low power consumption.
[0005]
The present invention has been made in view of such circumstances, and in order to achieve low power consumption when a sensor for detecting a fingerprint is mounted on a mobile device or the like, only when a finger is placed on the fingerprint sensor. It is an object of the present invention to provide a fingerprint detection circuit capable of turning on power.
[0006]
[Means for Solving the Problems]
The present invention is a fingerprint detection circuit comprising a two-dimensional array sensor and a detection circuit, wherein the scanning means scans a part of the output of the two-dimensional array sensor, and counts the number of output pulses from the scanning means. A counting unit, a determining unit that outputs a determination signal when a count value of the pulse by the counting unit exceeds a predetermined threshold, and a power supply that is supplied to the detection circuit when the determination signal is output. Power supply control means for turning on the power supply.
According to this configuration, it is determined whether or not a finger has been touched using a part of the output of the sensor, and power is supplied to the detection circuit only when it is determined that the finger has been touched. Low power consumption can be realized without operation.
[0007]
The present invention is characterized in that the scanning means scans the output of one or more sensor rows that are continuous in one of a vertical direction and a horizontal direction among the sensors constituting the two-dimensional array.
According to this configuration, since the output of one or more sensor rows that are continuous in any one of the vertical and horizontal directions is scanned, it is possible to efficiently detect peaks and valleys of continuous fingerprints, The output accuracy of the determination signal can be improved.
[0008]
Further, the invention is characterized in that the scanning means scans an output of a sensor array including a sensor near the center of the two-dimensional array.
According to this configuration, since the output of the sensor array including the sensor near the center is scanned, it is possible to improve the possibility of detecting a large amount of data at the peaks and valleys of the fingerprint.
[0009]
Further, the invention is characterized in that the determination means outputs a determination signal when the count value changes from a value below the threshold value to a value exceeding the threshold value.
According to this configuration, since the determination signal is output when the count value changes from a value equal to or less than the threshold value to a value exceeding the threshold value, the fingerprint image data is collected even when the finger is kept pressed. Further, power consumption can be further reduced without performing unnecessary operations.
[0010]
Further, according to the present invention, the power supply control means may turn off a power supply to the detection circuit when a signal indicating that scanning of all the sensors constituting the two-dimensional array sensor is completed is input. It is characterized by.
According to this configuration, when a signal indicating that the scanning of the sensor has been completed is input, the power supply to the detection circuit is turned off. And power consumption can be reduced.
[0011]
Further, according to the present invention, the scanning unit uses a part of the detection circuit, and the power supply control unit controls ON / OFF of power supply to a circuit of the detection circuit other than the scanning unit. Is performed.
According to this configuration, the scanning unit uses a part of the detection circuit, and the power supply control unit performs ON / OFF control of power supply to a circuit of the detection circuit other than the scanning unit. Therefore, a newly provided circuit can be realized with a simple configuration.
[0012]
Further, the invention is characterized in that the two-dimensional array sensor is a pressure-sensitive capacitance detection type sensor.
[0013]
According to another aspect of the present invention, there is provided an electronic apparatus including the fingerprint detection circuit.
[0014]
Further, the invention is characterized in that the electronic device activates a fingerprint detection application based on the determination signal.
According to this configuration, since the fingerprint detection application is started based on the determination signal, the load on the CPU provided in the electronic device can be reduced, and the power consumption of the fingerprint detection circuit can be reduced. In addition, power consumption can be further reduced.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a fingerprint detection circuit according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the embodiment. In this figure, reference numeral 1 denotes a two-dimensional array sensor of a pressure-sensitive capacitance detection type, which is constituted by 256 × 256 elements. This sensor detects peaks and valleys of a fingerprint by a change in a gap between a film and a substrate, and has a multi-value output value. In the following description, for the sake of simplicity, the arrangement of sensors in the horizontal direction of the two-dimensional array sensor 1 is referred to as “row”, and the arrangement of sensors in the vertical direction is referred to as “column”. Reference numeral 2 denotes a selector for selecting a “column” of the two-dimensional array sensor 1, and selects the column while switching from column 0 to column 255 in order. Reference numerals 30 to 3f denote 16 multiplexers (MUX) for selecting, multiplexing, and outputting "rows" of the two-dimensional array sensor 1. To each multiplexer, sensor outputs for 16 rows are input every 16 rows. That is, the output of the row corresponding to the value of the remainder (Mod (16) = 1 to 15) obtained by dividing 0 to 255 by 16 is input. Therefore, 16 rows of 15 rows, 31 rows, 47 rows, 63 rows, ..., 239 rows, and 255 rows are input to the multiplexer 3f. Reference numerals 40 to 4f denote amplifiers (AMP) for converting the outputs (capacities) of the multiplexers 30 to 3f into voltages. Reference numerals 50 to 5f denote sample and hold circuits (S / H) for holding the respective outputs of the amplifiers 40 to 4f. Reference numeral 6 denotes a multiplexer that multiplexes 16 outputs from the sample and hold circuits 50 to 5f into one signal. Reference numeral 7 denotes an AD converter that performs AD conversion on a signal output from the multiplexer 6. Digital data of a fingerprint image is obtained from the output of the AD converter. Reference numeral 8 denotes an interface (I / F) for transferring an AD-converted signal (digital data of a fingerprint image) to the fingerprint recognition processing.
[0016]
Reference numeral 9 denotes a timing controller that outputs a timing signal for scanning the output of the two-dimensional array sensor 1 to another circuit. Reference numeral 10 denotes a setting unit that sets a threshold value of a pulse count and a reference voltage of a comparator in order to determine whether a finger is placed on the two-dimensional array sensor 1. Reference numeral 11 denotes a comparator for comparing the output voltage of only one of the 16 amplifiers (here, the amplifier 4f) with the reference voltage provided by the setting unit 10. Reference numeral 12 denotes a counter that counts the number of pulses output from the comparator 11, and outputs a determination signal when a value exceeds a threshold value provided from the setting unit 10. Reference numeral 13 denotes a power supply control unit that performs ON / OFF control of the power supply to the detection circuit based on the determination signal output from the counter 12. The power supply control unit 13 controls the ON / OFF control of the power supply. The detection circuits include multiplexers 30 to 3e, amplifiers 40 to 4e, sample and hold circuits 50 to 5f, a multiplexer 6 and an AD converter 7, excluding the multiplexer 3f and the amplifier 4f. (A part surrounded by a broken line in FIG. 1).
[0017]
Next, with reference to FIG. 2, the operation of power supply ON / OFF control will be described. FIG. 2 is a flowchart showing the operation of ON / OFF control of power supply. First, when the power supply of the device provided with the fingerprint detection circuit shown in FIG. 1 is turned on, the setting unit 10 outputs a reference voltage to the comparator 11 in order to initialize the fingerprint detection circuit. I do. The setting unit 10 outputs a threshold value of the count value to the counter 12 (Step S1). This threshold value is about 50 to 100 when a 256 × 256 element array sensor is used and the output is multi-valued. At this time, the power control unit 13 outputs a power-off control signal to the detection circuit to be controlled to be turned on / off. As a result, power is not supplied to the detection circuit to be controlled for power ON / OFF at this time.
[0018]
Next, the counter 12 resets the count value according to the scanning start timing signal output from the timing controller 9 (Step S2). The selector 2 and the multiplexer 3f start a scanning operation. At this time, since power is not supplied to the detection circuit to be controlled to be turned on / off, only the amplifier 4f outputs a signal. The output of the amplifier 4f is compared with a reference voltage by the comparator 11, and when the output of the amplifier 4f is higher than the reference voltage, a signal of a comparison result is output from the comparator 11. Then, the counter 12 starts counting the number of pulses output from the comparator 11 (Step S3).
[0019]
Since the output of each element of the two-dimensional array sensor 1 is large at the peaks of the fingerprint and small at the valleys, the output between the amplifier output voltage when the sensor output is large and the amplifier output voltage when the sensor output is small. Is used as the reference voltage to be input to the comparator 11, only the output of the element touched by the peak of the fingerprint can be input from the comparator 11 to the counter 12. Since the output of the element touched by the valley is not output from the comparator 11, the pulse corresponding to the peak of the fingerprint is input to the counter 12.
[0020]
Next, the timing controller 9 outputs a signal of a scan end timing when the scanning (scanning for one frame) of all the sensors connected to the multiplexer 3f of the two-dimensional array sensor 1 is completed. Until this signal is input, that is, until the scanning is completed (step S4), the counter 12 continues the pulse counting, and the count value at the time when the scanning is completed is set to the threshold value given by the setting unit 10. Is determined (step S5). If not, the determination signal is not output, and the count value is reset according to the new scanning start timing. On the other hand, if the count value has exceeded the threshold value, the counter 12 outputs a determination signal to the power control unit 13 (Step S6). In response to this, the power control unit 13 outputs a power ON control signal to the power ON / OFF control target detection circuit (step S7). As a result, power is supplied to the power ON / OFF control target detection circuit, and scanning (scanning for one frame) of all the sensors of the two-dimensional array sensor 1 is performed according to the new scanning start timing. Digital data of the fingerprint image is transferred to the interface 8.
[0021]
Next, when the signal of the scan end timing is input from the timing controller 9, the power control unit 13 outputs a power-off control signal to the detection circuit to be controlled to be turned on / off (Step S <b> 8, S9). As a result, power is not supplied again to the detection circuit to be controlled.
[0022]
Here, an operation of determining a finger and an object other than the finger based on the output of the comparator 11 will be described with reference to FIGS. As shown in FIG. 3, when a finger touches the two-dimensional array sensor 1, the output of the amplifier 4 f (the output of 16 rows of 15 rows, 31 rows,. ) Is input and compared with the reference voltage, so that the comparator 11 outputs a large number (50 to 100) of pulses having a short pulse width corresponding to the peaks and valleys of the fingerprint. On the other hand, as shown in FIG. 4, when an object other than a finger touches the two-dimensional array sensor 1, the comparator 11 outputs a small number of pulses having a long pulse width corresponding to the size of the object. As described above, since the number of pulses is different between the case of the finger and the case of the non-finger, it is possible to consider that the finger touches the two-dimensional array sensor 1 by using an appropriate threshold value.
[0023]
In this way, it is determined whether or not a finger has been touched using only a circuit that can obtain an output of only a part of the sensor, and power is supplied to the entire fingerprint detection circuit only when it is determined that the finger has been touched. Since power is supplied, low power consumption can be realized without performing unnecessary operations. In particular, since an analog circuit such as an amplifier or an AD converter which consumes a large amount of power is stopped as much as possible and it is determined that a finger is touched with only a simple circuit, power can be used efficiently.
[0024]
Next, another embodiment will be described with reference to FIGS. FIG. 5 is a block diagram illustrating a configuration of a fingerprint detection circuit according to another embodiment. The fingerprint detecting circuit shown in FIG. 5 differs from the fingerprint detecting circuit shown in FIG. 1 in that a register 14 for storing a binary variable FON indicating whether or not the count value of the counter 12 has exceeded a threshold value is newly provided. It is a point. The flowchart shown in FIG. 6 differs from the flowchart shown in FIG. 2 in that steps S10 to S12 are newly added.
[0025]
In the operation illustrated in FIG. 2, when the finger is kept pressed, the ON / OFF control of the power ON / OFF control target detection circuit is repeatedly performed even after the fingerprint image data is collected. In order to further reduce power consumption, the fingerprint detection circuit illustrated in FIG. 5 performs an operation of keeping the detection circuit to be controlled to be turned on / off after collecting fingerprint image data even when a finger is kept pressed. It will be realized.
[0026]
First, when the power supply of the device provided with the fingerprint detection circuit shown in FIG. 5 is turned on, the setting unit 10 outputs a threshold value of the count value to the counter 12 in order to initialize the fingerprint detection circuit. Then, the value of FON of the register 14 is set to 0. (Step S1). Hereinafter, the same operation as in FIG. 2 is performed until step S5. If the count value does not exceed the threshold value in step S5, the value of FON is set to 0 (step S12), and the count value is reset according to a new scan start timing. On the other hand, if the count value exceeds the threshold value, it is determined whether the value of FON is 0 or 1 (step S10). If FON is not 0, it is determined that the finger has been kept pressed since the previous scan. Then, the count value is reset according to the new scanning start timing. On the other hand, if FON = 0, the value of FON is set to 1 (step S11), and the process proceeds to step S6. Hereinafter, the same operation as that of FIG. 2 is performed.
[0027]
As described above, even if the finger is kept pressed, the detection circuit to be controlled to be turned on / off can be maintained OFF after the fingerprint image data is collected. Can be realized.
[0028]
Next, an example in which the fingerprint detection circuit shown in FIGS. 1 and 5 is mounted on an electronic device will be described with reference to FIG. FIG. 7 is an explanatory diagram showing a state in which the fingerprint detection circuit shown in FIGS. As shown in this figure, if the two-dimensional array sensor 1 is provided on the operation surface of the mobile phone terminal, it can be applied to the authentication of payment when performing electronic commerce and the like. In addition, when the electronic device is implemented in this way, if the application for fingerprint detection is activated based on the determination signal output from the counter 12, the load on the CPU provided in the mobile phone terminal can be reduced. Therefore, in addition to reducing the power consumption of the fingerprint detection circuit, the power consumption can be further reduced. Also, it is conceivable to supply power to the fingerprint detection circuit when the fingerprint detection application starts, but in this case, if the time until the user tries to touch the finger according to the instruction of the application is long, the fingerprint is not printed. This is not preferable because the detection circuit consumes useless power. However, according to the present invention, when power is supplied to the fingerprint detection circuit, the time during which power is supplied to the fingerprint detection circuit can be set only to the time from when a finger touches to when a fingerprint image is read. As a result, power is consumed efficiently, resulting in power saving.
[0029]
In the above description, the sensor output of only 16 of the 256 rows is used to determine whether a finger has been touched. However, if the vicinity of the center of the two-dimensional array is included, one row is used. It may be determined whether or not a finger has touched using only the output. In this case, the threshold value of the count value may be reduced according to the number of sensor rows. In the above description, scanning in the horizontal direction (row direction) has been described as an example, but scanning may be performed in the vertical direction (column direction).
[0030]
【The invention's effect】
As described above, according to the present invention, it is determined whether or not a finger has been touched using only a circuit capable of obtaining an output of only a part of a sensor, and only when it is determined that a finger has been touched. Since power is supplied to the entire fingerprint detection circuit in this manner, it is possible to achieve an effect that low power consumption can be realized without performing unnecessary operations. In particular, since an analog circuit such as an amplifier or an AD converter which consumes a large amount of power is stopped as much as possible and it is determined that a finger is touched with only a simple circuit, power can be used efficiently.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an embodiment of the present invention.
FIG. 2 is a flowchart showing the operation of the circuit shown in FIG.
FIG. 3 is an explanatory diagram showing an operation of finger detection.
FIG. 4 is an explanatory diagram illustrating an operation of detecting an object other than a finger.
FIG. 5 is a block diagram showing a configuration of another embodiment of the present invention.
6 is a flowchart showing the operation of the circuit shown in FIG.
FIG. 7 is an explanatory diagram showing a state where the circuit shown in FIG. 1 is provided in an electronic device.
[Explanation of symbols]
1 ... two-dimensional array sensor (256 x 256 elements)
2. Selector 30 to 3f Multiplexer (MUX)
40-4f ... Amplifier (AMP)
50 to 5f ... Sample hold circuit (S / H)
6 Multiplexer (MUX)
7 AD converter 8 Interface (I / F)
9 timing controller 10 setting unit 11 comparator 12 counter 13 power control unit 14 register

Claims (9)

A fingerprint detection circuit comprising a two-dimensional array sensor and a detection circuit,
Scanning means for scanning a part of the output of the two-dimensional array sensor;
Counting means for counting the number of output pulses from the scanning means,
Determining means for outputting a determination signal when the count value of the pulse by the counting means exceeds a predetermined threshold,
A fingerprint control circuit for turning on power supplied to the detection circuit when the determination signal is output. 2. The fingerprint detection device according to claim 1, wherein the scanning unit scans an output of one or more sensor arrays, which are continuous in one of a vertical direction and a horizontal direction, of the sensors constituting the two-dimensional array. 3. circuit. 3. The fingerprint detection circuit according to claim 2, wherein the scanning unit scans an output of a sensor array including a sensor near a center of the two-dimensional array. 4. The fingerprint detection circuit according to claim 2, wherein the determination unit outputs a determination signal when the count value changes from a value lower than the threshold value to a value exceeding the threshold value. The power supply control unit turns off power supplied to the detection circuit when a signal indicating that scanning of all sensors constituting the two-dimensional array sensor has been completed is input. 5. The fingerprint detection circuit according to any one of 1 to 4. The scanning means uses a part of the detection circuit,
6. The fingerprint detection circuit according to claim 1, wherein the power supply control unit performs ON / OFF control of power supply to a circuit of the detection circuit other than the scanning unit. . 7. The fingerprint detection circuit according to claim 1, wherein the two-dimensional array sensor is a pressure-sensitive capacitance detection type sensor. An electronic device comprising the fingerprint detection circuit according to claim 1. The electronic device according to claim 8, wherein the electronic device activates a fingerprint detection application based on the determination signal.

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