JP2005156347A - Capacity detection circuit, its detection method and fingerprint sensor using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a capacity detection circuit and a detection method provided with a function for collecting independently both offset and sensitivity, capable of acquiring a stable detection value even when a measured value is fluctuated by initial dispersion or flaws or contaminations generated during use of a sensor or a detection circuit. <P>SOLUTION: This capacity detection circuit, which is a capacity detection circuit wherein row wires cross a plurality of column wires and a capacity change at the crossing part between a column wire and a row wire is detected as a voltage value, has a column wire driving means for driving the column wires, a capacity detection means connected to the row wires, for converting a current value corresponding to the capacity of the crossing part with the driving column wire into a measured voltage value and outputting the result, and a correction means for determining a correction factor from the plurality of measured voltage values and correcting the measured voltages by the correction factor. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a capacitance detection circuit and a detection method for detecting a minute capacitance, and a fingerprint sensor using the same.

  Conventionally, as the most promising fingerprint sensor in biometrics (biometric authentication technology), column wiring and row wiring are respectively formed on the surface of two films at predetermined intervals, and this film is interposed via an insulating film or the like. Thus, pressure-sensitive capacitive sensors have been developed that are arranged to face each other at a predetermined interval. In this pressure-sensitive capacitive sensor, when the finger is placed, the film shape changes corresponding to the unevenness of the fingerprint, the distance between the column wiring and the row wiring changes depending on the location, and the fingerprint shape changes between the column wiring and the row wiring. It is detected as the capacity of the intersection. In this pressure-sensitive capacitance sensor, it is necessary to detect a minute capacitance that is less than several hundred fF (femtofarad) at each intersection where the column wiring and the row wiring intersect.

Therefore, in the capacitance detection circuit, since the capacitance of the intersection is very small, not only is it required to have high sensitivity, but also variations in the initial sensitivity of the sensor due to manufacturing errors, circuit offset components, In addition, it is necessary to perform a process for suppressing the influence of the fluctuation of the capacitance value caused by the flaws and dirt adhering to the use.
As a conventional technique corresponding to the above-described problem, if the detection application is a fingerprint sensor, a signal in a non-detection state where a finger is not placed is detected, and this measurement value is used as two-dimensional correction data.

And when detecting a fingerprint, the method of correcting the measurement data in a detection state using the said correction data is proposed (for example, nonpatent literature 1). The specific correction method differs depending on the detection method of the fingerprint sensor, but in general, the two-dimensional data as correction data is subtracted from the two-dimensional data measured in the detection state, so that the dirt or dirt in the measurement data is reduced. An offset component due to a scratch or the like can be corrected.
IEICE Transactions C Vol.J86-C No.7 pp.665-673 (July 2003)

The conventional fingerprint detection circuit described above corrects the initial state as an offset component.
However, the above conventional detection circuit can correct the initial variation of the sensor, but corrects the fluctuation component over time during use such as dirt and scratches attached later as an offset component. I can't.
For this reason, this conventional detection circuit has a drawback that it is difficult to cope with variations in detection sensitivity and fluctuations after use, and cannot be applied to a fingerprint sensor or the like whose sensitivity is likely to fluctuate.

  The present invention has been made in view of the above circumstances, and its purpose is to provide an initial correction function for both the offset and the sensitivity so that the initial variation of the sensor and the detection circuit, and in use. It is an object of the present invention to provide a capacitance detection circuit, a detection method, and a fingerprint sensor that can obtain a stable detection value even if there is a change in measurement value due to scratches or dirt occurring in the sensor.

The capacitance detection circuit of the present invention is a capacitance detection circuit that detects a change in capacitance at a crossing portion of a column wiring and a row wiring as a voltage value by intersecting a row wiring with a plurality of column wirings, and drives the column wiring A column wiring driving means for converting, a capacitance detection means for converting a current value corresponding to a capacitance at an intersection of the driven column wiring connected to the row wiring to a measurement voltage value, and a plurality of the measurement voltages Correction means for obtaining a correction coefficient from the value and correcting the measured voltage with the correction coefficient.
As a result, the capacitance detection circuit of the present invention can obtain a correction coefficient for correcting the measurement voltage from a plurality of measurement voltage values, so that the offset component in the initial state and dirt or scratches attached later can be used. Since it is possible to independently obtain the correction coefficient for the time-dependent fluctuation component in, the fluctuation component that changes over time can also be corrected independently, and the measured voltage is corrected with high accuracy. be able to.

  In the capacitance detection circuit of the present invention, the correction unit drives the column wiring with a plurality of voltage values, and performs an operation for obtaining a correction coefficient based on the plurality of measured voltage values. Thus, it is possible to independently obtain correction coefficients for temporally varying components such as dirt and scratches attached later.

  In the capacitance detection circuit of the present invention, the correction means performs an operation for obtaining a correction coefficient from a plurality of measurement voltage values obtained by changing the number of column wirings to be driven. It is possible to independently obtain a correction coefficient for a temporal variation component such as dirt or scratches.

  In the capacitance detection circuit of the present invention, since the correction means obtains correction values for the offset and sensitivity from the plurality of measured voltage values, the offset component in the initial state and the time-lapse of dirt or scratches attached later. Since it is possible to independently obtain the correction coefficient for each fluctuation component, fluctuation components that change over time can be corrected independently, and the measured voltage can be corrected with high accuracy. .

  In the capacitance detection circuit of the present invention, the correction means determines whether or not the capacitance is being detected based on the measured voltage value, and calculates the correction value when it is determined that the detection is not being performed. Since the calculation is performed periodically, the correction coefficient used to correct the fluctuation component that changes over time can be adjusted for each predetermined period, and correction corresponding to the fluctuation component can be performed. Can be requested.

  Since the fingerprint sensor according to the present invention includes the capacitance detection circuit described above, the measurement voltage is effectively corrected as described above in response to a change in the measurement environment over time. And detection with high accuracy.

  The capacitance detection method of the present invention is a capacitance detection method in which a row wiring intersects a plurality of column wirings, and a capacitance change at the intersection of the column wiring and the row wiring is detected as a voltage value, and the column wiring is driven. A column wiring driving process, a capacitance detection process for converting a current value corresponding to a capacitance at an intersection of the driven column wiring connected to the row wiring to a measured voltage value, and a plurality of the measured voltages A correction coefficient is obtained from the value, and the correction voltage is corrected by the correction coefficient.

  As described above, according to the capacitance detection circuit of the present invention, by obtaining a plurality of measurement voltage values, a correction coefficient for correcting the measurement voltage can be obtained from the calculation using these measurement voltage values. It is possible to independently obtain the correction coefficient for the offset component of the state and the time-dependent fluctuation component such as dirt and scratches attached later. Therefore, the measured voltage can be corrected with high accuracy.

  A capacitance detection circuit according to the present invention is a capacitance detection circuit that detects a change in capacitance at a crossing of a column wiring and a row wiring as a voltage value by intersecting a row wiring with a plurality of column wirings. A column wiring driving unit (column wiring driving means) to be driven and a capacitance detection unit (connected to the row wiring and corresponding to the capacitance at the intersection with the driven column wiring are converted into measurement voltage values and output. (Capacitance detection means) and a calculation control section, and a correction value calculation section (correction value calculation means) for obtaining a correction coefficient from a plurality of measurement voltage values and correcting the measurement voltage with the correction coefficient.

  1 is recorded on a computer-readable recording medium, and the program recorded on the recording medium is read into a computer system and executed to execute capacity detection. Processing may be performed. Here, the “computer system” includes an OS and hardware such as peripheral devices. The “computer system” includes a WWW system having a homepage providing environment (or display environment). The “computer-readable recording medium” refers to a storage device such as a flexible medium, a magneto-optical disk, a portable medium such as a ROM and a CD-ROM, and a hard disk incorporated in a computer system. Further, the “computer-readable recording medium” refers to a volatile memory (RAM) in a computer system that becomes a server or a client when a program is transmitted via a network such as the Internet or a communication line such as a telephone line. In addition, those holding programs for a certain period of time are also included.

  The program may be transmitted from a computer system storing the program in a storage device or the like to another computer system via a transmission medium or by a transmission wave in the transmission medium. Here, the “transmission medium” for transmitting the program refers to a medium having a function of transmitting information, such as a network (communication network) such as the Internet or a communication line (communication line) such as a telephone line. The program may be for realizing a part of the functions described above. Furthermore, what can implement | achieve the function mentioned above in combination with the program already recorded on the computer system, and what is called a difference file (difference program) may be sufficient.

Hereinafter, a capacitance 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 a configuration example of the embodiment.
The drive control unit 1 controls the voltage of a driving pulse for driving the column wiring by the column wiring driving unit 5, that is, the driving voltage of the column wiring.
The column wiring driving unit 5 generates a driving pulse of the driving voltage and drives each column wiring in the sensor unit 4 in which the column wiring and the row wiring intersect to form a sensor.
In the sensor unit 4, the column wirings of the column wiring group 2 and the row wirings of the row wiring group 3 intersect in a matrix, and each intersection forms a sensor element (sensor element 55 in FIG. 4).

  2A is a plan view of the sensor unit 4, and FIG. 2B is a cross-sectional view. As shown in FIG. 2A, for example, each column wiring of the column wiring group 2 and each row wiring of the row wiring group 3 arranged at a pitch of 50 μm intersect each other. As shown in FIG. 2B, a row wiring group 3 composed of a plurality of row wirings is arranged on a substrate 50, an insulating film 51 is laminated on the surface, and only a gap 52 is formed on the surface of the insulating film 51. The film 54 is disposed with a space therebetween, and the column wiring group 2 including a plurality of column wirings is attached to the lower surface of the film 54. A sensor element 55 is formed as a capacitive element having a predetermined capacitance through the gap 52 and the insulating film 51 at the intersection of the row wiring of the row wiring group 3 and the column wiring of the column wiring group 2.

When the finger 56 is put on the sensor unit 4 described above, the film 54 and the column wiring of the column wiring group 2 are deformed due to the unevenness of the finger 56 as shown in FIG. The capacitance of the sensor element 55 formed at the intersection between the column wiring group 2 and the row wiring group 3 changes.
FIG. 4 is a conceptual diagram showing a matrix of capacitive elements (sensor elements) between the column wirings and the row wirings of the sensor unit 4. The sensor unit 4 is composed of matrix-like sensor elements 55, 55..., And the column wiring drive unit 5 and the capacitance detection circuit 100 are connected to each other. The column wiring driving unit 5 outputs a driving pulse train to the column wiring group 2, that is, sequentially outputs a predetermined driving pulse (driving signal) to the column wirings of the column wiring group 2 of the sensor unit 4.

1, the capacitance detection circuit 100 includes a charge amplifier circuit 6, a sample hold circuit 7, a selector circuit 8, an A / D converter 9, a measurement value calculation unit 10, a timing control circuit 11, and a correction value calculation unit 12. Have.
The charge amplifier circuit 6 is provided in each row wiring in the row wiring group 3 of the sensor unit 4, and enters and exits according to the capacitance of the intersection (sensor element) (based on the charge / discharge current). Current corresponding to the amount of change) is detected, the current is amplified and converted into a voltage (IV conversion) and output as a detection signal (measurement voltage).

The sample hold circuit 7 is provided for each charge amplifier circuit 6 and samples the measurement voltage of the detection signal by inputting the sampling hold signal, and temporarily holds it as voltage information.
The selector circuit 8 switches the voltage information held in each of the sample and hold circuits 7 sequentially, for example, in the row arrangement order, and outputs the voltage information to the A / D converter 9 for each row wiring unit.
The A / D converter 9 converts the measurement voltage, which is analog voltage information input in time series, into measurement data of a digital value at the timing of the A / D clock input from the measurement value calculation unit 10. And output to the measured value calculation unit 10.

Further, when processing at a high speed, the A / D converter 9 is provided in each charge amplifier circuit 6 without providing the sample hold circuit 7, and the analog measurement voltage is converted into digital measurement data. You may do it.
The correction value calculator 12 obtains an offset value (offset component) of initial variation and a sensitivity correction coefficient that is a fluctuation component from the digitized measurement voltage value.

In the digitized measurement data, the measurement value calculation unit 10 corrects the measurement data at the time of charging the sensor element at the intersection and the measurement data at the time of discharging with the correction coefficient and the offset value, and at the time of charging after the correction. And the calculation process which removes the offset component by feedthrough by the difference calculation of the measurement data at the time of discharge is performed.
When the timing control circuit 11 receives a start signal indicating that the capacitance detection is started from the measurement value calculation unit 10, the drive control unit 1, the column wiring drive unit 5, the charge amplifier circuit 6, the sample hold circuit 7, Then, a clock and a control signal are output to the selector circuit 8 and the like, and the operation timing of the entire capacitance detection circuit 100 is controlled.

Further, as shown in FIG. 5, the drive control unit 1 includes a voltage control circuit 1a and a drive voltage regulator 1b. In a normal capacitance measurement state, the drive voltage of the drive pulse for the column wiring is a predetermined value. It has become.
However, during the detection operation for obtaining the correction coefficient and the offset value, the voltage control circuit 1a outputs a request signal for requesting a change in the drive voltage to the drive voltage regulator 1b as necessary, and the drive voltage regulator 1b receives the request signal. Is supplied to the column wiring drive unit 5.

Then, the drive control unit 1 supplies the drive voltage to the column wiring drive unit 5, and the column wiring drive unit 5 outputs a drive pulse to each column wiring by the supplied predetermined drive voltage.
The column wiring drive unit 5 is composed of a single pulse generation circuit 22, a shift register 23, driver circuits 51,.
The single pulse generation circuit 22 is synchronized with the clock input from the timing control circuit 11 and is input to the register 231 of the shift register 23 every time the number of clocks corresponding to the number of stages of the shift register 23, that is, the number of registers is input. On the other hand, a single pulse of “1” is supplied.

The shift register 23 sequentially shifts the single pulse input to the register 23 1 to the register adjacent in the right direction every time the clock is input from the timing control circuit 11.
That is, in the shift register 23, a data “1” shift operation is performed every time a clock is input in the order of the registers 23 1 → 23 2 → 234 →... → 2313 → 2314 →.
.., 2314,... Are connected to driver circuits 51, 52, 53,... 514,. The circuit is activated, and the drive pulse of the drive voltage supplied from the drive voltage regulator 1b is output to the corresponding column wiring.

The outputs of the registers 231, 232, 233,..., 2314,. Here, when the data to be shifted is “1” (drive data), the drive signal is output to the corresponding driver circuit, and when the data is “0”, the drive signal is not output.
In the case of FIG. 5, the driver circuit 51 outputs a drive pulse to the column wiring C1, and none of the other driver circuits 52, 53,.
The outputs of the driver circuits 51, 52, 53,..., 514,... Are connected to the column wirings C1, C2, C3,.
That is, in each register of the shift register 23, the drive data is shifted in time series, so that the column wiring is sequentially driven correspondingly.

  Next, the configuration of the charge amplifier circuit 6 will be described with reference to FIG. FIG. 6 is a conceptual diagram showing a configuration example of the charge amplifier circuit 6. As shown in this figure, the charge amplifier circuit 6 includes an operational amplifier 121 and a feedback capacitor connected between the inverting input terminal and the output terminal of the operational amplifier 121. Cf and an analog switch 124 for discharging the charge of the feedback capacitor Cf. The non-inverting input terminal of the operational amplifier 121 is connected to the reference potential. In FIG. 6, Cp is a parasitic capacitance of the operational amplifier 121, Cs is a capacitance of the sensor element at the intersection (the sum of multiplexed sensor elements), and Cy is a sensor element with respect to a column wiring that is not detected. Total capacity.

Next, the operation of the charge amplifier circuit 6 will be described in detail. First, when the reset signal is output from the timing control circuit 11 at time td1 slightly before time t1 shown in FIG. 10, the analog switch 124 (MOS transistor, FIG. 6) is turned on, and the feedback capacitor Cf is discharged. The output OUT of the operational amplifier 121 is short-circuited with the inverting input terminal and becomes a reference potential. In addition, the row wiring connected to the inverting input terminal of the operational amplifier 121 also becomes the reference potential.
Next, when this reset signal is turned off, the output voltage of the operational amplifier 121 slightly rises due to feedthrough due to the gate parasitic capacitance of the analog switch 124 (see the symbol Fd after time td1 in FIG. 10A).

  When the drive pulse rises (inputs) at time t1, the drive pulse is applied to the inverting input terminal of the operational amplifier 121 via the sensor element (capacitance Cs) at the intersection of the column wiring and the row wiring. Due to the current flowing based on the voltage value of the drive pulse, the voltage value of the output OUT of the operational amplifier 121 gradually decreases as shown in FIG.

Next, at time td2, the timing control circuit 11 outputs a sample hold signal (S / H signal) to the sample hold circuit 7. Thereby, the sample hold circuit 7 holds the measurement voltage Va output from the output OUT of the operational amplifier 121 in the charge amplifier circuit 6 at the time when the sample hold signal is input.
Next, at time td3, the timing control circuit 11 outputs a reset signal to the charge amplifier circuit 6 again. As a result, the output OUT of the operational amplifier 121 and the inverting input terminal are short-circuited, the feedback capacitor Cf is discharged, and the output OUT of the operational amplifier 121 returns to the reference potential. When the reset signal is turned off, the output voltage of the operational amplifier 121 slightly increases due to the feedthrough due to the gate parasitic capacitance of the analog switch 124 as in the case described above (reference Fd after time td3 in FIG. 10A). reference).

Next, at time td4, when the drive pulse in the drive pulse train P1 falls, the column wiring driven by the drive pulse and the sensor element (capacitance Cs) at the intersection of the row wiring are based on the voltage of the drive pulse. As a result, the output OUT of the operational amplifier 121 gradually rises.
Next, at time td5, the timing control circuit 11 outputs a sample hold signal to the sample hold circuit 7. Thereby, the sample hold circuit 7 holds (holds) the measurement voltage Vb of the output OUT of the operational amplifier 121 at the time when the sample hold signal is input.
Next, at time td6, the timing control circuit 11 outputs a reset signal to the charge amplifier circuit 6. As a result, the output OUT of the operational amplifier 121 and the inverting input terminal in the charge pump circuit 6 are short-circuited, the feedback capacitor Cf is discharged, and the output OUT of the operational amplifier 121 returns to the reference potential. Thereafter, the above operation is repeated.

In the measurement described above, the offset Vk due to the feedthrough current of the analog switch 124 is generated in the + direction regardless of whether the output OUT drops from the reference potential or rises. As in this embodiment, when the capacitance Cs to be detected is tens to hundreds of femtofarads, the offset due to this feedthrough cannot be ignored. In the above measurement,
-Va0 = -Va + Vk
Is a voltage proportional to the detection target capacitance Cs, but the measured voltage is Va, and this voltage Va includes an error Vk due to an offset.
Va = Va0 + Vk

Therefore, in this embodiment, the voltage Vb at the time of discharging the detection target capacitor Cs is also measured. Here, the voltage Vb0 = Vb-Vk
Is a voltage proportional to the capacitance Cs, and the measured voltage is Vb = Vb0 + Vk
It becomes. These measurement voltages Va and Vb are sequentially held by the sample hold circuit 7, and then the held voltage is A / D converted by the A / D converter 9 for each of the measurement voltages Va and Vb. Stored in the internal memory. And in the measured value calculation unit 10,
d = Vb-Va = (Vb0 + Vk)-(Vk + Va0) = Vb0-Va0
As a result, measurement data d that does not include an offset error, that is, measurement data d (measurement data D0a, D0b, Dma, Dmb, etc. to be used later) corresponding to the multiplexed capacitance value is obtained.

  As described above, the measurement value calculation unit 10 obtains the difference between the output signals of the charge amplifier circuit 6 when the potential of the column wiring is raised and when the drive line rises and falls. The capacitance value of the sensor element can be measured in a state where there is no influence of feedthrough. Further, by providing the selector, the charge amplifier circuit 6 that requires measurement time can be measured in parallel in each column wiring, and the measurement speed of the entire sensor can be increased.

Next, calculation processing for obtaining the correction coefficient and offset value in the correction value calculation unit 12 will be described.
FIG. 7 shows a conceptual diagram of a conventional correction method in order to explain the present invention in an easy-to-understand manner in comparison with the conventional example.
In the conventional example, in an initial state where a detection target such as a finger is not placed, a detection value is obtained at a predetermined position of the sensor unit (points a and b in FIG. 7A), and this is used to correct an offset. As a standard.

In this method, correction is performed in accordance with the state where there is no detection target (the state of FIG. 7B is corrected to FIG. 7C), so that the offset value is removed in the stationary state, and the desired correction operation is performed. To do. That is, the detected value is corrected so that the measured voltages at the points a and b are equal.
However, in this correction, the sensitivity gradient is not corrected, and only the correction of the offset value due to the initial variation or the like is performed.
For this reason, when there is a detection target (a finger or the like is placed), the sensitivity (capacity / measurement voltage relationship, that is, the relationship between the sensitivity gradient ka and kb) is not corrected, and thus the sensitivity variation Due to the influence, an error occurs in the detected value (measured voltage) (FIG. 7D).

Next, the principle of correction using the correction value for the offset value and the correction coefficient for the sensitivity according to the first embodiment of the present invention will be described with reference to FIG.
The electric charge Q generated in the intersection capacitance C when the column wiring is driven with the driving voltage V is represented by Q = CV as shown in FIG.
Therefore, even when there is no detection target, the amount of charge with respect to the capacitance value can be changed by changing the drive voltage when the capacitance at the intersection has a certain value.

For example, as shown in FIG. 8B, if the voltage of the drive pulse is M times the predetermined drive voltage, the amount of change in the detected value should be M times correspondingly.
Therefore, during the operation period for obtaining the correction coefficient and the offset value, first, the measurement data DOa is obtained with the normal drive voltage, and then the measurement data Dma (M · D0a) is obtained by multiplying the drive voltage by M times. (The slope ka is also M times M · ka.)
Here, assuming that the drive voltage is constant, it is equivalent to the fact that the virtual capacity when the drive voltage is multiplied by M is apparently M times the actual capacity value.
Therefore, as shown in FIG. 8C, even when there is no detection target, it is possible to obtain the same change in detection value as when the capacitance is changed substantially.
Then, the relationship of the detection value (measurement voltage) to the capacitance value change at each intersection, that is, the sensitivity gradient ka (hereinafter referred to as sensitivity) can be obtained.

Next, with reference to FIG. 9, a specific measurement operation for the sensitivity correction coefficient and the offset correction value will be described.
A flow for obtaining the offset value and the sensitivity correction value from the measurement data DOa and Dma corresponding to the drive voltage will be described. Here, the measurement data DOa and Dma are obtained by converting the measured voltage into digital values by the AD converter 9, and the following calculation processing of the correction value of the offset value and the correction coefficient of the sensitivity is the correction value calculation. This is performed by the unit 12.
First, an average value or a predetermined set value of the measurement data DOa of the entire sensor unit 4 is used as reference data D0, and a correction value α for the offset value of the capacitance at this intersection is obtained for each intersection.
α = DOa−D0

Next, a difference Δa between the measurement data DOa and the measurement data Dma is obtained. This difference Δa is the amount of change in the detected value when the detection capacity becomes M times, and thus corresponds to the sensitivity of each intersection as described above.
For this reason, an average value or a predetermined set value of the difference Δa is set as a reference difference Δa0, and the sensitivity correction coefficient β of the intersection is calculated for each intersection.
Here, the difference Δa is
Δa = Dma−D0a
Therefore, the correction coefficient β is
β = Δa0 / Δa = Δa0 / (Dma−D0a)
As required.

As described above, the correction value calculation unit 12 calculates the correction value α for correcting the offset value and the correction coefficient β for correcting the sensitivity.
And the measured value calculating part 10 correct | amends the measurement data Di corresponding to the capacity | capacitance of each intersection part based on the following formula | equation. The correction data Dc for each intersection is
Dc = ((Di-α-D0) × β) + D0
This is obtained as a corrected result by

For example, as a numerical example, in the detection operation for obtaining the correction value and the correction coefficient, when using M = 3, that is, three times the drive voltage with respect to the normal drive voltage, the reference detection value is set to D0a = 50, Consider the case where the reference displacement when M = 3 is Δa 0 = 100.
Here, assuming that the intersection point a has a detection value at the same level as the reference value, the measurement data D0a = 50 when a normal drive voltage is applied, and the drive is M times the normal drive voltage. When a voltage is applied, measurement data Dma = 150.
At this time, since the correction coefficient α = 0 and the correction coefficient β = 1, the corrected result when the normal drive voltage is applied is Dc0a = 50, and the correction when the normal M-fold drive voltage is applied. As a result, that is, the correction data at the point a is Dcma = 150, which is equal to the relationship between the measurement data D0a and Dma.

On the other hand, assuming that the intersection point b has a deviation (offset value) corresponding to the detected value of the capacitance at the intersection, and the sensitivity has a deviation of 1.1 times. As each detection value, in the correction value calculation unit 12, the measurement data D0b when a normal drive voltage is applied is:
D0b = (50 + 10) × 1.1 = 66
The measurement data Dmb when a drive voltage M times the normal drive voltage is applied is
Dmb = 66 × 3 = 198
Is required.

At this time, similarly, the correction value calculator 12 calculates the correction value α and the correction coefficient β at the intersection point b as follows. The correction value α is
α = (66−50) = 16
The difference Δb between the measurement data Dmb when a drive voltage M times (three times) the normal drive voltage at the point b is applied and the measurement data D0b when the normal drive voltage is applied is Δb = 198-66 = 132
As required. The sensitivity correction coefficient β is β = 100/132
As shown in FIG. 9B, the offset value and the sensitivity can be corrected corresponding to the reference (here, point a).

Therefore, when the measurement value calculation unit 10 corrects the measurement data DOb and the measurement data Dmb with the obtained correction value α and correction coefficient β,
Dc0b = ((66-16-50) × 100/132) + 50 = 50
And is the same as the numerical value of the correction data Dc0a corrected at the point a when a normal driving voltage is applied,
Dcmb = ((198-16-50) × 100/132) + 50 = 150
As shown in FIGS. 9C and 9D, the points a and b are the same as the numerical values of the correction data Dcma obtained as a result of correcting the point a when the M-fold drive voltage is applied. It can be seen that the detected values correspond to each other and are corrected well.
As described above, it can be seen that the correction value α corrects the offset value and the correction coefficient β corrects the sensitivity, and the correction processing between the correction value calculation unit 12 and the measurement value calculation unit is effectively performed. .

Next, an operation for determining the calculation timing of the offset correction value α and the sensitivity correction coefficient β will be described with reference to FIG. FIG. 11 is a flowchart showing a flow of processing for detecting the calculation timing.
In step S <b> 1, the measurement value calculation unit 10 has a timer inside, and detects whether or not a predetermined time interval set in advance has elapsed.
Here, when the measured value calculation unit 10 detects that the predetermined time has elapsed, the process proceeds to step S2, and when it is determined that the predetermined time has not elapsed, the operation of step S1 is repeated.

Next, in step S <b> 2, the measurement value calculation unit 10 obtains the measurement data of the capacity of each intersection in the sensor unit 4, and obtains the difference value between the maximum value and the minimum value of the measurement data for each obtained intersection.
In addition, the measurement value calculation unit 10 calculates an average value of all measurement data at the intersection in the sensor unit 4.
In step S3, the measurement value calculation unit 10 detects whether the difference value exceeds a preset threshold value.
At this time, when the measurement value calculation unit 10 detects that the difference value exceeds the threshold, the measurement process for correction ends (restarts the process from step S1), while the difference value Is detected to be equal to or less than a predetermined threshold value, the process proceeds to step S4.

Here, when measurement data for obtaining a correction value and a correction coefficient is measured, it is necessary to perform measurement when there is no target to be detected, that is, in a non-detection state. Accordingly, when the difference value does not exceed the threshold value, it is determined that there is no detection target (if the fingerprint is detected, no finger is placed), and measurement data for obtaining a correction value and a correction coefficient is measured.
When the difference value exceeds the threshold value, it is assumed that there is a detection target (if a fingerprint is detected, a finger is placed), and measurement data for obtaining a correction value and a correction coefficient is not measured.

Next, in step S4, the measured value calculator 10 detects whether or not the difference between the average value and the initial value exceeds a preset reference value.
At this time, when the measurement value calculation unit 10 detects that the difference exceeds the standard value, the measurement process for correction is ended (again, the process is started again from step S1). If it is detected that the value is equal to or less than the predetermined standard value, the process proceeds to step S5.

Here, the measurement value calculation unit 10 calculates the difference between the average value of the measurement data of each intersection at the time of fingerprint detection in the sensor unit 4 and the average value of each intersection in the non-fingerprint detection state at the time of manufacture. The above standard value is obtained. It is experimentally set to an appropriate value by experimenting how many times the average value difference can be set as the standard value to distinguish between fingerprint detection and non-fingerprint detection. For example, the standard value is obtained by adding 1/2 of the average value difference to the average value of each intersection in the non-fingerprint detection state.
And the measured value calculating part 10 considers that there is no detection object, if the average value of each cross | intersection part does not exceed the said standard value.

Next, in step S5, the measurement value calculation unit 10 measures the measurement data necessary for calculating the correction value and the correction coefficient by the processing described above, and outputs the necessary measurement data to the correction value calculation unit 12. To do.
As a result, as described above, the correction value calculation unit 12 calculates the correction value and the correction value for each intersection from the measurement data obtained by the normal drive voltage and the drive pulse of the drive voltage M times the drive voltage. A correction coefficient is obtained, stored in the internal storage unit in correspondence with each intersection, and when correction processing is performed at the time of fingerprint detection, the correction value and the correction coefficient at the corresponding intersection are read, and the measured value calculation unit 10 Output to.
Then, the measurement value calculator 10 corrects the measurement data using the correction value and correction coefficient input from the correction value calculator 12.

Next, a capacitance detection circuit according to a second embodiment of the present invention will be described with reference to FIG. The same components as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.
The configuration different from the first embodiment is that the drive control unit 1A does not change the drive voltage of the drive pulse like the drive control unit 1, but controls the number of column wirings to be driven.
At the time of fingerprint detection, as in the first embodiment, as shown in FIG. 12, one column wiring of the column wiring group 2 is activated one by one, and a fingerprint detection operation is performed.
Here, the drive control unit 1A will be described with reference to FIG. The drive control unit 1A includes a drive pulse generation circuit 1Aa and a pulse control circuit 1Ab.
When the fingerprint is detected, the drive control unit 1A outputs a predetermined pulse width, that is, a single pulse, and sequentially outputs data “1” (drive data) according to the clock from the timing control circuit 11 to each register of the shift register 23. Shift in.

On the other hand, during the detection operation of the correction value and the correction coefficient used for correcting the measurement data, the pulse width control circuit 1Ab of the drive control unit 1A receives a control signal for performing the detection operation from the measurement value calculation unit 10. In response to the clock from the timing control circuit 11, a signal instructing the drive pulse generation circuit 1Aa is output to a plurality of registers in the shift register 23 so as to output a pulse having a width in which the data “1” is input. .
As a result, the drive pulse generation circuit 1Aa outputs a pulse having a time width in which the data “1” is input to a plurality of registers in the shift register 23, that is, three registers.
Therefore, the plurality of driver circuits of the column wiring driving unit 5A simultaneously activate a plurality of column wirings, for example, three column wirings (shown by hatching) as shown in FIG. Then, driving the plurality of column wirings, and driving each of the column wirings that are simultaneously driven, to obtain an offset correction value and a sensitivity correction coefficient for each column wiring. Become.

Next, the principle of correction using a correction value for an offset value and a correction coefficient for sensitivity in the second embodiment of the present invention will be described with reference to FIG.
The charge Q generated in the intersection capacitance C when the column wiring is driven with the drive voltage V is represented by Q = CV as shown in FIG.
Therefore, when the number of column wirings to be driven is plural, for example, three, the number of intersections where the charge Q is generated is tripled.
Strictly speaking, the capacity differs at each intersection, but there is almost no difference in capacity in a stationary state, so it can be considered that the capacity has tripled.

For this reason, even when there is no detection target, if the capacitance at the intersection has a certain value, the amount of charge detected can be changed by changing the number of column wirings to be driven.
For example, as shown in FIG. 14B, when the number of column wirings to be driven is M, which is M times, the detected charge amount is M times, and the change amount of the detected value is also M times correspondingly. Will be.

That is, during the measurement data detection period for obtaining the correction value and the correction coefficient, first, the detection value DOa is obtained with the normal number of column wirings (one), and the number of column wirings to be driven is M times the detection value Dma ( M · D0a).
Here, assuming that the number of column wirings to be driven is constant (for example, one), this is equivalent to the fact that the virtual capacity is apparently M times the actual capacity.
As a result, as shown in FIG. 14C, the same change in the detected value as that obtained when the capacitance is substantially changed even in the stationary state can be obtained.

Next, with reference to FIG. 9, a specific measurement operation for the sensitivity correction coefficient and the offset correction value will be described.
A flow for obtaining the offset correction value and the sensitivity correction coefficient from the measurement data D0a and the measurement data Dma corresponding to the number of column wirings to be driven will be described. Here, the measurement data D0a and the measurement data Dma are obtained by converting the measured measurement voltage into digital values by the AD converter 9, and the following calculation processing of the correction value of the offset value and the sensitivity correction coefficient is the correction value. This is performed by the calculation unit 12.

First, an offset correction value α at each intersection is obtained using an average value or a predetermined set value of the measurement data DOa of the entire sensor unit 4 as a reference DO.
α = D0a−D0
Next, a difference Δa between the measurement data DOa and the measurement data Dma is obtained. This difference Δa is the amount of change in the detected value when the detection capacity becomes M times, and thus corresponds to the sensitivity of each intersection as described above.
Therefore, the average value of the difference Δa or a predetermined set value is set as the reference difference Δa0, and the sensitivity correction coefficient β is calculated.
Here, the difference Δa is
Δa = Dma−D0a
Therefore, the correction coefficient β is
β = Δa0 / Δa = Δa0 / (Dma−D0a)
As required.

As described above, the correction value calculator 12 obtains the correction value α for correcting the offset value and the correction coefficient β for correcting the sensitivity for each intersection.
And the measured value calculating part 10 correct | amends the measurement data Di corresponding to the capacity | capacitance of each intersection part based on the following formula | equation. The correction data Dc for each intersection is
Dc = ((Di-αi-D0) × βi) + D0
This is obtained as a corrected result by

For example, as a numerical example, in the detection operation for obtaining the correction value and the correction coefficient, when M = 3, that is, the number of column wirings to be driven is three times the normal number of column wirings to be driven, the reference detection value is Consider the case where D0a = 50 and the reference displacement when M = 3 is Δa0 = 100.
Here, assuming that the point a at the intersection has a detection value at the same level as the reference value, the measurement data D0a = 50 in the case of the normal number of column wirings (one), which is a normal M-fold number. When the column wiring is driven, the measurement data Dma = 150.
At this time, since the correction coefficient α = 0 and the correction coefficient β = 1, the corrected result when the number of column wirings to be normally driven is correction data Dc0a = 50, and the number of column wirings to be normally driven is M times. In this case, the corrected result is correction data Dcma = 150, which is equal to the correspondence relationship between the measurement data D0a and Dma already described.

On the other hand, assuming that the intersection b has a deviation (offset value) corresponding to the detected value of the capacitance at the intersection, the driving column is assumed to have a deviation of 1.1 times. As the respective detection values for the number of wires, in the correction value calculation unit 12, the measurement data D0b when the number of column wires to be normally driven is
D0b = (50 + 10) × 1.1 = 66
The measurement data Dmb when driving the usual M times the number of column wirings is
Dmb = 66 × 3 = 198
Is required.

At this time, similarly, the correction value calculator 12 calculates the correction value α and the correction coefficient β at the intersection point b as follows. The correction value α is
α = (66−50) = 16
The measurement data Dmb when driving the column wiring M times (three times) the column wiring to be normally driven at the point b, and the number of driving of the normal column wiring (for example, the center of the three column wirings) The measurement data D0b and the difference Δb at the time of selecting one and obtaining the correction value and correction coefficient for each intersection are Δb = 198−66 = 132
As required. The sensitivity correction coefficient β is β = 100/132
As shown in FIG. 9B, the offset value and the sensitivity can be corrected corresponding to the reference (here, point a).

Therefore, when the measurement value calculation unit 10 corrects the measurement data DOb and the measurement data Dmb with the obtained correction value α and correction coefficient β,
Dc0b = ((66-16-50) × 100/132) + 50 = 50
And is the same as the numerical value of the corrected result D0a of the point a when the number of column wirings to be driven is normal,
Dcmb = ((198-16-50) × 100/132) + 50 = 150
As shown in FIGS. 9 (c) and 9 (d), the detection value corresponds to the numerical value of the corrected result Dma of the point a when driving the normal M-number of column wirings. , You can see that it is well corrected.

As described above, it can be seen that the correction value α corrects the offset value and the correction coefficient β corrects the sensitivity, and the correction processing between the correction value calculation unit 12 and the measurement value calculation unit is effectively performed. .
The operation of determining the calculation timing of the offset correction value α and the sensitivity correction coefficient is performed by the process of the flowchart of FIG. 11 as in the first embodiment.

It is a block diagram which shows the structure of the fingerprint sensor using the capacity | capacitance detection circuit by the 1st Embodiment of this invention. It is a conceptual diagram which shows the structural example of the sensor part 4 in FIG. It is a conceptual diagram explaining the measurement of the fingerprint data using the sensor part 4 in FIG. 5 is a conceptual diagram illustrating a configuration example of a sensor element 55 formed at each intersection of a column wiring of the column wiring group 2 and a row wiring of the row wiring group 3 in the sensor unit 4 of the area sensor type. FIG. FIG. 2 is a block diagram illustrating a configuration example of a drive control circuit 1 and a column wiring drive unit 5 in FIG. 1 (first embodiment). FIG. 2 is a conceptual diagram illustrating a configuration example of a sensor unit 4 and a charge amplifier circuit 6 in FIG. 1. It is a conceptual diagram explaining the correction process of the conventional offset value. It is a conceptual diagram explaining the calculation process of the correction value of an offset value and the correction coefficient of a sensitivity in the 1st Embodiment of this invention. It is a conceptual diagram explaining the calculation process of the correction value of an offset value and the correction coefficient of a sensitivity in the 1st Embodiment of this invention. FIG. 6 is a waveform diagram for explaining the operation of a detection signal and charge amplifier circuit 6; It is a flowchart which shows the operation example which calculates | requires correction value detection timing. FIG. 2 is a block diagram illustrating a configuration example of a drive control circuit 1A and a column wiring drive unit 5A in FIG. 1 (second embodiment). In the 2nd Embodiment of this invention, it is a conceptual diagram explaining operation | movement of 5 A of column wiring drive parts when driving the number of column wiring of M times with respect to normal drive. It is a conceptual diagram explaining the calculation process of the correction value of an offset value and the correction coefficient of a sensitivity in the 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,1A ... Drive control part 1a ... Voltage control circuit 1b ... Drive voltage regulator 1Aa ... Drive pulse generation circuit 1Ab ... Pulse width control circuit 2 ... Column wiring group 3 ... Row wiring group 4 ... Sensor part 5, 5A ... Column wiring drive 5, 5 2, 5 3, 5 4, 5 5, 5 6, 5 7, 5 8,... Driver circuit 59, 510, 511, 512, 513, 514, driver circuit 6, charge amplifier circuit 7, sample hold circuit 8, selector circuit 9, A / D converter 10 ... measurement value calculation unit 11 ... timing control circuit 12 ... correction value calculation unit 22 ... single pulse generation circuit 23 ... shift register 50 ... substrate 51 ... insulating film 52 ... gap 54 ... film 100 ... capacitance detection circuit C1 ... Column wiring R1 ... Row wiring

Claims (7)

It is a capacitance detection circuit that detects a change in capacitance at a crossing portion of a column wiring and a row wiring as a voltage value by intersecting a row wiring with respect to a plurality of column wirings,
Column wiring driving means for driving the column wiring;
Capacitance detecting means connected to the row wiring and converting the current value corresponding to the capacitance at the intersection with the driven column wiring into a measured voltage value, and
A capacitance detection circuit comprising: a correction unit that obtains a correction coefficient from a plurality of the measurement voltage values and corrects the measurement voltage by the correction coefficient.   2. The capacitance detection circuit according to claim 1, wherein the correction means drives the column wiring with a plurality of voltage values and obtains a correction coefficient from the plurality of measured voltage values to be measured.   2. The capacitance detection circuit according to claim 1, wherein the correction means obtains a correction coefficient from a plurality of measured voltage values obtained by changing the number of column wirings to be driven.   4. The capacitance detection circuit according to claim 1, wherein the correction unit obtains a correction value for each of an offset and a sensitivity from the plurality of measured voltage values. 5.   5. The correction unit according to claim 1, wherein the correction unit determines whether or not a capacitance is being detected based on the measured voltage value, and calculates a correction value when it is determined that the detection is not being performed. The capacitance detection circuit described.   A fingerprint sensor comprising the capacitance detection circuit according to claim 1. A row detection method is a capacitance detection method for detecting a change in capacitance at a crossing portion of a column wiring and a row wiring as a voltage value by intersecting a row wiring with respect to a plurality of column wirings.
A column wiring driving process for driving the column wiring;
A capacitance detection process for converting a current value corresponding to a capacitance at an intersection with the driven column wiring connected to the row wiring to a measured voltage value and outputting the measurement voltage value;
A capacity detection method comprising: obtaining a correction coefficient from a plurality of the measured voltage values, and correcting the measured voltage by the correction coefficient.

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