JPH0381171B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a drive circuit for a matrix electrode for detecting a fingerprint pattern using a pressure-sensitive conductive material.

(Prior Art) Conventionally, matrix electrodes have been used to measure the distribution of pressure acting on a surface or to detect the pressed state of a key on a keyboard switch. The present invention also proposes a pressure detection method using such a matrix electrode in place of the conventional optical detection method for detecting fingerprint patterns in Japanese Patent Application No. 62-35489.

Figure 9 shows a drive circuit for a conventional fingerprint pattern detection matrix electrode using a _pressure -sensitive conductive material _.
It was shown as The matrix electrodes are a plurality of (three in the illustrated example) parallel line electrodes KD ₁ , KD ₂ , KD ₃ , which are driven by the matrix driver 1 .
... and multiple (three in the illustrated example) parallel line electrodes KR ₁ connected to the matrix receiver 2,
KR ₂ , KR ₃ , ... are arranged so as to cross each other with a pressure-sensitive conductive material in between. A pressure-sensitive conductive material has a resistance characteristic in which the resistance value changes as shown in Figure 10 depending on the strength of the pressure applied to it, so when pressure is applied near the intersection of the line electrodes, the resistance of that part changes. The value decreases and the line electrodes KD ₁ , KD ₂ , KD ₃ ,...
Line electrode KR ₁ of the drive signal outputted through ,
Since the level of the signal received by the matrix receiver 2 via KR ₂ , KR ₃ , . . . becomes the highest, it is possible to determine which intersection is pressurized.
For example, when pressure is applied to the intersection point A shown with diagonal lines, the resistance value R ₁ at that point is the smallest, so the line electrode is connected to the matrix driver 1.
The drive signal output via KD ₂ is connected to line electrode KD _1.
It can be determined that the intersection area A is pressurized based on the signal level when the signal flows into the matrix receiver 2 via the .

However, in such a matrix electrode,
Intersection area B, C, and D are pressurized and intersection area A
If we consider the case where is not pressurized, the resistance values R ₂ , R ₃ , and R ₄ near the intersection points B, C, and D will decrease, similar to the case where the intersection point A is pressurized. , line electrode from matrix driver 1
The drive signal outputted via KD ₂ is inputted to the matrix receiver 2 through the line electrode KR ₂ via the resistance value R ₂ , so that pressurization at the intersection point B is determined, and the drive signal is transferred from the matrix driver 1 to the line electrode KD _{3 .} The drive signal outputted through the resistor _R3 passes through the line electrode _KR2 , and is also input to the matrix receiver ₂ through the line electrode KR1 via the resistor _R4 , so the intersection points C and D Pressure is determined. As long as this is the case, it is possible to accurately determine the pressurizing point. However, regarding intersection point A,
Because it is not pressurized, even if the drive signal is output from the matrix driver 1 via the line electrode KD ₂ , it will not be input to the matrix receiver 2 via the line electrode KR ₁ , but it will be input via the line electrode KD ₂ . The drive signal to be output is as shown by the broken line in the figure.
Once connected to the line electrode via the resistance _R2 at the intersection point B
KR ₂ , then flows to line electrode KD ₃ via resistance R ₃ at intersection point C, then flows to line electrode KR ₁ via resistance R ₄ at intersection point D, and is input to matrix receiver 2. This detour signal causes the intersection area A to be erroneously determined as if it were pressurized.

Therefore, in order to prevent such misjudgment due to signal wraparound, as shown in FIG. 11, diodes D ₁ to D ₉ for preventing wraparound are connected to resistors r ₁ to r ₉ at each intersection point between the intersecting line electrodes. A method of connecting in series has been proposed (for example, in
No. 234418). With this circuit configuration, for example, for the above loop signal, diode _D4
Since the flow is in the opposite direction to the flow of the drive signal, it is possible to prevent the signal from going around, and it is possible to accurately determine whether or not the intersection is pressurized just by the resistance value between the line electrodes at the intersection. .

A matrix electrode drive circuit that uses diodes to prevent signal wraparound in this way requires a number of wraparound prevention diodes equal to the number of matrix intersection points, and a circuit for forming or inserting the diodes is required. Although space is required, when the unevenness of fingerprints becomes extremely fine, such as 4 lines per 1 mm, as in the case of fingerprint detection, it is necessary to provide an extremely large number of intersection points, and each intersection point must be designed to prevent wraparound. Providing a diode for this would make the product difficult due to space considerations. Further, along with this, the matrix circuit also requires a substrate such as a semiconductor wafer, which increases the cost. It is thought that approximately 90,000 intersection points of matrix electrodes are required to detect a fingerprint pattern, so the number of diodes to prevent wraparound would also be 90,000, making mass production difficult and almost impossible.

(Objective and Structure of the Invention) The present invention has been made in view of the above points, and it is possible to prevent signal loop-around by devising a driving method without providing a diode for preventing signal loop-around, and to install many line electrodes in a small space. In order to achieve this purpose, multiple drive line electrodes connected to a driver circuit that outputs drive signals and a receiver circuit sequentially select A driver circuit sequentially applies drive signals to the drive line electrodes and maintains line electrodes to which no drive signal is applied at a constant potential with low impedance. It was configured as follows.

(Example) The present invention will be explained below based on the drawings.

FIG. 1 is a block diagram of an embodiment of a driving circuit for a matrix electrode for fingerprint pattern detection according to the present invention. The matrix electrode illustrated here is incorporated into a fingerprint input board used for detecting fingerprint patterns, and 10 is the fingerprint input board, whose structure is shown in Fig. 2. Press the finger F whose fingerprint you want to detect on the screen as shown by the chain line. This fingerprint input board 10 has line electrodes KD ₁ , KD ₂ ,
KD ₃ , . . . and KR ₁ , KR ₂ , KR ₃ , . . . are arranged so as to be electrically insulated and orthogonal to each other. Reference numeral 11 is a data driver similar to the matrix driver ₁ explained in FIG.
It is sequentially sent as a drive signal to KD ₂ , KD ₃ , . . . at predetermined time intervals. 13a, 13b, 13c, . . . are C-MOS inverters connected to the line electrodes KD ₁ , KD ₂ , KD ₃ , . . . , and 14 is a data receiver similar to the matrix receiver 2 shown in FIG. The signals of KR ₁ , KR ₂ , KR ₃ , ... are selected and received in sequence and are output in time series as fingerprint signals. Reference numeral 15 denotes a low-noise amplifier that amplifies the fingerprint signal output from the data receiver 14, and the fingerprint signal amplified by this amplifier 15 is then subjected to necessary processing for registration, discrimination, etc.

Now, the fingerprint input board 10 has a plurality of line electrodes on the bottom surface of an insulating substrate 10a made of alumina, glass, or epoxy, as shown in the cross-sectional structure in FIG.
KR ₁ , KR ₂ , KR ₃ , ... (one of them, KR ₁ is shown as an example in the figure) are formed by vapor deposition, etc., and a plurality of line electrodes KD ₁ , KD ₂ , KD ₃ , ... are formed on the upper surface. are formed in a similar manner.

On the other hand, on the upper surface of the insulating substrate 10a, as shown in FIG. 3, line electrodes KR ₁ ,
Line electrodes KD ₁ , KD 2 , KD ₃ , KD 1 , KD 2 , KD 3 , KD 1 , KD ₂ , KD ₃ , etc. along KR ₂ , KR 3 , … have wide lands LR on the upper surface.
... are formed slightly apart from each land LR and the line electrodes KR ₁ , KR ₂ , KR ₃ , ... on the lower surface.
and are electrically connected to each other through the insulating substrate 10a near the intersection of both line electrodes. In addition, line electrodes formed on the upper surface of the insulating substrate 10a
Lands LD are also formed at positions KD ₁ , KD ₂ , KD ₃ , . . . corresponding to the lands LR.
In addition, in Figure 3, lands LR and LD are shown for example so that they can be distinguished for each crossing point of the line electrodes.
They are indicated by reference numbers such as LR ₁₁ , LD ₁₁ .

Returning to FIG. 2 again, on the insulating substrate 10a on which the line electrodes are formed, the land is placed on the insulating plate 10b made of ABS resin or alumina.
LR or LD spacing (this spacing is
A pressure-sensitive conductive material 10c having a diameter of approximately 30 .mu.m and a pressure plate 10c embedded therein is placed, which is equal to the distance between the intersection points of the line electrodes formed on the upper and lower surfaces of the holder, for example, about 50 .mu.m. The pressure-sensitive conductive material 10c is formed to be approximately several tens of micrometers higher than the surface of the insulating plate 10b, and when a finger is pressed against the top surface of this pressing plate during fingerprint detection, the convex part or ridge of the fingerprint on the fingertip is The pressure-sensitive conductive material 10c is contracted before the insulating substrate 10b. FIG. 4 is a top view of the fingerprint input board 10.

Next, the circuit operation of the drive signal shown in FIG. 1 will be explained.

The data driver 11 receives an AC signal with a frequency of about 1 MHz output from the oscillator 12 and sequentially sends it to C-MOS inverters 13a, 13b, 13c, . . . . A C-MOS inverter has a structure as shown in FIG. 5, for example, and when the output is at the "L" level, the resistance to the ground is less than 0.01Ω, so it can almost be considered to be at ground potential. The signals output from the C-MOS inverters 13a, 13b, and 13c are drive signals delayed by a certain period of time as shown in FIG. 6, and when a drive signal is output to a certain line electrode (for example, line electrode KD ₁ ), are other line electrodes (e.g. line electrodes KD ₂ and KD ₃ )
The potential of is almost the ground potential.

Now, when I put my finger on the fingerprint input board 10 and pressed it to detect a fingerprint pattern, the intersection point A shown in FIG. 7 was not pressed, and the other intersection points B, C, and D were the ridges of the fingerprint. Suppose that it is pressurized by . Now, in order to determine the pressurized state of the intersection point A, suppose that the data driver 11 outputs a drive signal as shown in FIG. 6 to the line electrode KD ₂ and the data receiver 14 selects the line electrode KR ₁ . The drive signal flowing through the line electrode KD ₂ is connected to the resistors R ₂ and R ₃ of the pressurized intersection points B and C.
It flows through the line electrode KD ₃ , which is at ground potential, as shown by the broken line in the figure, and does not wrap around the line electrode KR ₁ . Although the intersection point D is also pressurized, the line electrode KD ₃ is at ground potential, so there is no wraparound to the line electrode KR ₁ . line electrode
The drive signal of KD ₂ flows into the line electrode KR ₁ only through the path passing through the resistance R ₁ at the intersection point A.
This determines that the intersection point A is not pressurized.

Now, if we consider the magnitude of the signal input to the data receiver 14 via the line electrode _KR1 ,
It is considered that resistors R ₁ , R ₄ , and R ₅ as shown in FIG. 8A are connected to all the intersections having electrodes on one side of the intersections of the matrix electrodes connected to the line electrode KR ₁ , Electrically, the equivalent circuit is as shown in FIG. 8B. As a result, the signal input to the data receiver 14 via the line electrode KR ₁ is attenuated, and for example, the resistors R ₁ , R ₄ ,
If R is ₅ , it will be attenuated to 1/3. Similarly, for n line electrodes, the attenuation is 1/n.

The fingerprint signal thus obtained from the data receiver 14 is amplified by the low-noise amplifier 15 to a level suitable for the next processing.
For safety reasons, an amplification factor of about 2n is sufficient. For example, if the line electrodes are 300×300 matrix electrodes, the amplification factor of the amplifier 15 may be about 300×2=600.

As an example, if a matrix electrode with 300 x 300 line electrodes is used, the number of intersection points will be 90,000, and if a drive signal consisting of four clocks with a frequency of 1 MHz is output to one intersection point, all intersection points will be is 4μmsec×90000=0.36 seconds,
Fingerprint patterns can be detected in about 0.5 seconds.

When a fingerprint pattern is detected using the matrix electrode drive circuit according to the present invention, it is sufficient to determine whether or not the pressure-sensitive conductive material near each intersection point has been pressed based on the ridges of the fingerprint, and the strength of the pressing force is sufficient. Since there is no need to detect the height of the fingerprint pattern, when the fingerprint data is subsequently processed, it can be determined that the intersections where there is no signal even after amplification are the valleys of the fingerprint pattern, and the other intersections are the peaks of the fingerprint pattern.

In the above embodiment, an alternating current signal from an oscillator was used to measure the pressure surface distribution, but it goes without saying that a direct current signal may also be used. However, the level of the signal input to the data receiver is relatively low, and this tends to be the case as the number of line electrodes increases. Therefore, AC signals are preferable in terms of ease of signal amplification and S/N ratio.

Furthermore, in the above embodiment, when applying a drive signal from the data driver to the line electrodes, the drive signal is always applied to one line electrode and the other line electrodes are maintained at ground potential. The same thing may be done for the line electrode connected to the data receiver instead of the line electrode connected to the data receiver.

Further, among the line electrodes connected to the data driver, the line electrodes to which no drive signal is applied are set to the ground potential, but the line electrodes are not limited to the ground potential, but may be any other potential as long as they are at a constant potential.

(Effects of the Invention) As explained above, in the present invention, a plurality of drive line electrodes connected to a driver circuit that outputs a drive signal and a plurality of selection line electrodes that are sequentially selected by a receiver circuit are connected to a driver circuit that outputs a drive signal. The line electrodes are arranged to intersect with each other, and the driver circuit sequentially applies a drive signal to the drive line electrodes, and the line electrodes to which no drive signal is applied are maintained at a constant potential with low impedance. It is possible to prevent wraparound without using diodes, FETs, or other elements. This eliminates the need for space to install elements such as diodes and FETs, which were conventionally used to prevent signal loop-around, making it possible to reduce circuit space or increase circuit density by that amount, making it possible to use devices such as fingerprint pattern detection. This makes it possible to realize extremely high-density matrix electrodes.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of a drive circuit for a matrix electrode for fingerprint pattern detection according to the present invention, FIG. 2 is a partial cross-sectional view of a fingerprint input board, and FIG. 3 is a diagram of a matrix electrode used in the fingerprint input board. FIG. 4 is a plan view of the fingerprint input board, FIG. 5 is a specific example of the C-MOS inverter used in the matrix electrode drive circuit shown in FIG. 1, and FIG. 6 is a perspective view showing the positional relationship of the line electrodes. An example of a drive signal applied to an electrode, FIG. 7 is a matrix circuit for explaining prevention of signal loop-around in a drive circuit for a matrix electrode for fingerprint pattern detection according to the present invention, and FIG.
Figure A is a circuit diagram explaining the level of the fingerprint signal obtained in the present invention, B is an equivalent circuit of the circuit shown in A, and Figure 9 explains the occurrence of signal wraparound in the conventional drive circuit of the matrix electrode for fingerprint pattern detection. An example of this is shown in Figure 10, which shows the resistance characteristics of a pressure-sensitive conductive material.
FIG. 1 is a diagram illustrating prevention of signal loop-around in the conventional matrix electrode drive circuit shown in FIG. 9. 10...Fingerprint input board, 10c...Pressure-sensitive conductive material, 11...Data driver circuit, 13a, 13
b, 13c...C-MOS inverter, 14...
Data receiver, 15...amplifier.

Claims (1)

[Claims] 1. A plurality of drive line electrodes arranged in parallel, and a plurality of selection electrodes electrically insulated from the drive line electrodes and arranged in parallel to intersect with the drive line electrodes. The line electrode is arranged near the intersection of the driving line electrode and the selection line electrode, and electrically connects the driving line electrode and the selection line electrode through a resistance value that corresponds to the strength of the pressing force. a plurality of pressure-sensitive conductive members to be connected; a driver circuit that sequentially outputs a drive signal to the drive line electrodes and maintains line electrodes to which no drive signals are output at a constant potential; and a driver circuit that sequentially selects the selection line electrodes. 1. A drive circuit for a matrix electrode for fingerprint pattern detection, comprising a receiver circuit for outputting a pressure signal. 2. A plurality of driving line electrodes arranged in parallel, a plurality of selection line electrodes electrically insulated from the driving line electrodes and arranged in parallel so as to intersect with the driving line electrodes, and the driving line electrodes arranged in parallel. A plurality of pressure sensitive electrodes are arranged near the intersection of the drive line electrode and the selection line electrode and electrically connect the drive line electrode and the selection line electrode through a resistance value that corresponds to the strength of the pressing force. A conductive member, a driver circuit that sequentially outputs a drive signal to the drive line electrodes, and a receiver circuit that sequentially selects the selection line electrodes and maintains unselected line electrodes at a constant potential. A drive circuit for matrix electrodes for fingerprint pattern detection.