TW201624347A - Fingerprint detecting device - Google Patents

Abstract

The present invention relates to a fingerprint detecting device having a substrate, multiple pixel units and a detecting circuit. The pixel units are formed on the substrate and each pixel unit has a first and second electrode parts connected to the detecting circuit. The detecting circuit drives the first electrode part by a first driving voltage and also drives the second electrode part by a second driving voltage. After then, the detecting circuit receives a first and second sensing capacitance signals from the first and second electrode parts, and generate an output according to the first and second sensing capacitances signals. The output is used as a sensing capacitance information of the driven pixel unit. A fingerprint information is generated by the sensing capacitance information from the pixel units. Therefore, noise influences of the sensing capacitance signal of each pixel unit can be reduced and the detecting accuracy is increased.

Description

Fingerprint sensing device

The invention relates to a fingerprint sensing device, in particular to a fingerprint sensing device for avoiding noise interference.

At present, the capacitive fingerprint sensing device mainly has two types of surface type and line type. As shown in FIG. 5A and FIG. 5B, the capacitive fingerprint sensing device is formed on a substrate 50 and has a plurality of pixel electrode regions arranged in a matrix. 51. In the face capacitive fingerprint sensing device with a resolution of 500 dpi, in order to obtain the finest feature of the ridge and the concave width of the adult finger fingerprint of about 150 micrometers, each pixel electrode region 51 has a size of about 50 micrometers*50. The micro-pixel; therefore, the pixel electrode 51 corresponds to at least one complete ridge or recess, and each of the pixel electrode regions 51 is provided with a single electrode 511.

As shown in FIG. 5C, each pixel electrode 51 of the capacitive fingerprint sensing device is connected to a pixel detecting circuit, and includes a comparing circuit 60, a detecting switch sw, a driving source Vdd, and a first a reference signal source V _R and a second reference signal source Vref; wherein the inverting input terminal (-) of the comparison circuit 60 is connected to the first reference signal source V _R and is connected to the corresponding one through the detection switch sw The electrode 511 of one of the pixel electrode regions 51 and the driving source Vdd are switchably connected between the detecting switch sw and the electrode 511 of the pixel electrode region 51. The non-inverting input terminal (+) of the comparison circuit 60 is connected to the second reference signal source Vref. As shown in FIG. 6A, when the detection switch sw is turned off, the driving source Vdd outputs a driving signal to the opposite electrode 511 of the pixel electrode region 51, and the first reference signal source V _R provides a reference. After the voltage, as shown in FIG. 6B, the driving source Vdd and the first reference signal source V _{R are} turned off, and the detecting switch sw is turned on, and the inverting input terminal (-) of the comparing circuit 60 is obtained. A capacitive sensing signal from the electrode 511 of the pixel electrode region 51 is compared with a reference signal of the second reference signal source Vref to output a comparison result. Since the electrode 511 of the pixel electrode region 51 has different capacitance sensing values corresponding to the ridge portion and the concave portion of the fingerprint, an image corresponding to the fingerprint can be generated according to the comparison result.

However, the pixel detecting circuit corresponding to the electrode 511 of each of the pixel electrode regions 51 determines that the portion corresponding to the electrode 511 of the pixel electrode region 51 is the ridge or the concave portion of the fingerprint by the capacitance sensing signal, and the capacitance sensing The signal includes a capacitance value C _F between the electrode 511 of the pixel electrode region 51 and the ridge or the recess, and further includes a capacitance value of the ridge or the recess to the ground EGND, wherein the potential of the capacitance value C _BODY is It will be changed by the noise interference V _N . Therefore, as shown in FIG. 7A , the first waveform SV1 displays the detected voltage value corresponding to different coupling capacitance values, that is, the coupling capacitance value and the detected voltage, which are not interfered by noise. The V _OP value is proportional, so the corresponding coupling capacitance value can be identified according to the detection voltage magnitude, and then the portion corresponding to the electrode 511 of the pixel electrode region 51 is determined as the ridge or the concave portion of the fingerprint according to the coupling capacitance value; A noise waveform S _NOISE interference shown in FIG. 7B is as shown in the second waveform SV2, and the detected voltage value of the pixel detecting circuit is obviously oscillated up and down with the noise waveform S _NOISE , so that the coupling capacitance value and the detected power are generated. The pressure values are no longer proportional to each other, which greatly affects the judgment of the fingerprint ridge or the concave portion and the detection of the fingerprint image; therefore, it is necessary to further improve it.

In view of the above disadvantages that the fingerprint sensing device is susceptible to noise interference and the accuracy of fingerprint image recognition is reduced, the main object of the present invention is to provide a fingerprint sensing device for avoiding noise interference.

The main technical means for achieving the above purpose is that the fingerprint sensing device comprises a substrate, a plurality of pixel units and a fingerprint sensing circuit; wherein the plurality of pixel units are disposed on the substrate, and each of the pixel units includes a a first electrode portion and a second electrode portion, wherein the fingerprint sensing circuit is connected to the plurality of pixel units, and includes: a plurality of driving units respectively connected to the pixel unit, each of the driving units being connected to the corresponding pixel The first and second electrode portions of the unit drive the first electrode portion with a first driving voltage, and drive the second electrode portion with a second driving voltage different from the second driving voltage And a plurality of sensing units respectively connected to the pixel unit, each of the sensing units receiving a first capacitive sensing signal corresponding to the first electrode portion in the pixel unit and a second capacitive sensing signal of the second electrode portion, And performing an operation according to the first and second capacitive sensing signals to generate an output as the capacitive sensing information of the pixel unit, wherein each of the pixel units Capacitive sensing information is used to generate a fingerprint information.

In the above, the first and second electrode portions are disposed in a pixel unit corresponding to the size of one pixel electrode region, and the driving units connecting the first and second electrode portions are first and second with different voltages. After the driving voltages are respectively driven, the sensing units connected to the first and second electrode portions respectively receive and operate according to the two capacitance sensing signals of the first and second electrode portions to generate a comparison result, and the comparison result is The capacitive sensing signal of the pixel unit is used to eliminate the capacitance component caused by the same noise interference; thus, the capacitive sensing signal of each pixel unit of the present invention has a capacitive sensing signal compared to the electrode of the existing pixel electrode region, that is, does not include noise interference. The resulting capacitance component improves the recognition accuracy of fingerprint influence.

Referring to FIG. 1A and FIG. 1B , the fingerprint sensing device of the present invention comprises a substrate 10 and a plurality of pixel units 11 , wherein the plurality of pixel units 11 are correspondingly disposed on one side of the substrate 10 , and the substrate can be a glass cover or a protective layer of the fingerprint sensing device, and each of the pixel units 11 includes a plurality of electrode portions. The number of electrode portions of each of the pixel units 11 in the embodiment is selected as two embodiments. In the embodiment shown in FIG. 1B, the first electrode portion 111 and each of the second electrode portions 112 are two independent and have the same area. Moreover, the adult-based finger print has a ridge and a recess width of about 150 micrometers. To obtain the finest feature of the fingerprint, in the 500 dpi fingerprint sensing device, the pixel unit 11 is currently about 50 micrometers*50. Therefore, the first and second electrode portions 111, 112 of the pixel unit 11 largely correspond to the same portion on the fingerprint at the same time, wherein the actual design size of the present invention is not limited to the foregoing size.

Referring to FIG. 1C, the fingerprint sensing device of the present invention further includes a fingerprint sensing circuit 20 connected to the plurality of pixel units 11 and including a plurality of driving units and a plurality of sensing units; and the plurality of pixel units 11 and The fingerprint sensing circuit 20 can be integrated on the same wafer, and the plurality of pixel units 11 are correspondingly located on the side of the substrate 10. The plurality of driving units are respectively connected to the pixel unit 11, and each driving unit is connected to the first and second electrode portions 111 and 112 of the corresponding pixel unit 11, and the first and the second are different by two voltages. The two driving voltages drive the first electrode portion 111 and the second electrode portion 112, respectively. The plurality of sensing units are also respectively connected to the first and second electrode portions 111 and 112 of the pixel unit 11 , and each sensing unit is configured to receive the first electrode portion 111 corresponding to the pixel unit 11 . a capacitive sensing signal and a second capacitive sensing signal of the second electrode portion 112, and performing an operation according to the first and second capacitive sensing signals to generate an output as the capacitive sensing information of the pixel unit 11, wherein each of the pixels The capacitive sensing information of unit 11 is used to generate a fingerprint information, that is, to form a fingerprint image.

Referring to the embodiment shown in FIG. 1C, each of the sensing units includes a differential circuit 22 having a non-inverting input terminal (+) and an inverting input terminal (-). The input terminal (+) is connected to the corresponding first electrode portion 111 through a first switch S1, and the inverting input terminal (-) is connected to the corresponding second electrode portion 112 through a second switch S2; The inverting input terminal (+) and the inverting input terminal (-) are switchably connected to a first and second reference voltage source V _R1 through two switches S12 and S22 (shown at node N2 as shown in FIG. 2A ). V _R2 . Each of the driving units includes a first driving voltage source V _D1 and a second driving voltage source V _D2 ; wherein the first driving voltage source V _D1 is transmitted through a switch S11 (shown at node N1 as shown in FIG. 2A ). Switchably connected between the first switch S1 and the first electrode portion 111 to provide the first driving voltage of the first electrode portion 111 of the pixel unit 11 to which the corresponding pixel unit 11 is connected, and the second driving The voltage source V _D2 is switchably connected between the second switch S2 and the second electrode portion 112 through another switch S21 (shown at the node N1 as shown in FIG. 2A) to provide a pixel unit corresponding thereto. The second driving voltage of the second electrode portion 112 of 11. In an embodiment, each of the differential circuits can be a differential amplifier.

At time T1, an equivalent circuit as shown in FIG. 2A, wherein the difference circuit 22 is a differential amplifier of gain A, and the first and second switches S1 and S2 are turned off, and the first unit of the driving unit is The second driving voltage sources V _D1 and V _D2 simultaneously and respectively provide the first and second driving voltages to the corresponding first and second electrode portions 111 and 112 of the pixel unit 11 , and at the same time, the first The second reference voltage source V _R1 , V _R2 is switched to be connected to the non-inverting input terminal (+) and the inverting input terminal (−) of the differential circuit 22; wherein C _P1 is a parasitic capacitance of the node N1, that is, from The non-inverting and inverting input terminals (+) and (-) of the differential circuit 22 see the equivalent capacitance, and C _P2 is the equivalent capacitance of the node N2, but does not include the first electrode portion 111 and the second electrode. Portion 112 does not correspond to the coupling capacitance C _{F of the} finger. Then at time T2, the equivalent circuit shown in FIG. 2B, that is, the switches S11 and S21 of the first and second driving voltage sources V _D1 and V _D2 are disconnected from the first and second reference voltage sources V _R1 and V _{R2 .} The switches S12 and S22 are turned on to turn on the first and second switches S1 and S2, so that the first and second electrode portions 111 and 112 are respectively connected to the non-inverting and inverting inputs of the differential circuit 22 (+ ), (-), respectively receiving the first and second capacitive sensing signal V and the second electrode of the first portions 111, 112 _1, V _2, after the operation and then be output a comparison result.

As shown in FIG. 2A, the capacitance of a finger to the earth EGND is C _BODY , and the other end of the capacitor C _BODY is disturbed by noise due to noise interference, and it is assumed that the noise of the noise is disturbed at time T1. The finger potential is V _f1 , and FIG. 2B is subjected to noise interference at time T2 and the finger potential is V _f2 . Then, the first capacitive sensing signal voltage V of the non-inverting input terminal (+) in the equivalent circuit of FIG. 2B ₁ can be derived from the following expression: Reorder , the above formula can be organized as: , after finishing as follows: Similarly, the voltage V ₂ of the second capacitive sensing signal of the inverting input terminal (-) is: Of which . The operation of the differential amplifier includes subtracting the first capacitive sensing signal V ₁ from the second capacitive sensing signal V ₂ to obtain an output voltage V _OP of: According to this equation, the output voltage V _OP does not include V _f1 and V _f2 , so noise interference is eliminated. Further, if the voltages of the first and second reference voltage sources V _R1 and V _R2 are further the same, , the output voltage of the differential circuit is: Where A is the gain parameter.

It can be seen from the above formula that the first and second electrode portions 111, 112 of the same pixel unit 11 are relatively close, which substantially corresponds to the same portion on a single fingerprint, and the first electrode shown in FIG. 1B The portion 111 and each of the second electrode portions 112 include the same area, that is, the capacitance values C _F of the first and second electrode portions 111 and 112 of the same pixel unit 11 are very close. Even if there is noise interference, the first and second capacitive sensing signals V ₁ and V ₂ also include the same varying voltage that is interfered by the same noise (as shown in FIG. 5B ). Therefore, after the difference circuit 22 operates, The comparison result can exclude the varying voltage V _N having the same noise interference as shown by the second waveform SV2 of FIG. 4A.

Referring to FIG. 3A , each of the pixel units 11 includes a plurality of first electrode portions 111 and a plurality of second electrode portions 112 , for example, each of which includes two first electrode portions 111 and two second electrode portions 112 , and The total area of the two first electrode portions 111 is the same as the total area of the two second electrode portions 112. Similarly, as shown in FIG. 3B, each of the pixel units 11 includes three first electrode portions 111 and three second electrode portions 112, or as shown in FIG. 3C, each of the pixel units 11 includes a first electrode portion 111. And four second electrode portions 112. In addition, as shown in FIG. 3C , if each of the pixel units 11 is to add an electrode of another function, at least one spare electrode 12 may be disposed at an intermediate position of the pixel unit 11 , and the plurality of first electrode portions 111 and the plurality The second electrode portion 112 is surrounded.

When the pixel unit 11 includes the plurality of first electrode portions 111 and the plurality of second electrode portions 112, the plurality of first electrode portions 111 and the plurality of electrodes 13 of the plurality of second electrode portions 112 are staggered in the pixel unit 11 in. That is, the first and second electrode portions 111 and 112 of the pixel unit 11 in a first direction X are staggered, and the first of the pixel units 11 is located in a second direction Y. The first and second electrode portions 111, 112 are also staggered as shown in Figs. 3A to 3C.

In summary, the present invention mainly provides at least one first and second electrode portions in a pixel unit corresponding to the size of one pixel electrode region, and causes the driving units connecting the first and second electrode portions to have different voltages. After the first and second driving voltages are respectively driven, the sensing units connected to the first and second electrode portions respectively receive and calculate according to the two capacitance sensing signals of the first and second electrode portions to generate a comparison result. The comparison result is the capacitance sensing signal of the pixel unit to eliminate the influence of the same noise interference, which helps to improve the recognition accuracy of the fingerprint influence.

While the invention has been described in connection with the preferred embodiments described above, it is not intended to limit the scope of the invention. The technical scope of the invention is protected, and therefore the scope of the invention is defined by the scope of the appended claims.

10‧‧‧Substrate
11‧‧‧Pixel unit
111‧‧‧First electrode section
112‧‧‧Second electrode
12‧‧‧ spare electrode
20‧‧‧Fingerprint sensing circuit
22‧‧‧Differential circuit
50‧‧‧Substrate
51‧‧‧pixel electrode area
511‧‧‧pixel electrode
60‧‧‧Comparative circuit

FIG. 1A is a schematic structural view of a fingerprint sensing device of the present invention. Figure 1B is an enlarged view of a portion of the structure of Figure 1A. Figure 1C is a schematic diagram of a portion of the structure (side view) and fingerprint sensing circuit of Figure 1A. 2A and 2B are schematic diagrams showing the operation of the driving and receiving circuits of the fingerprint sensing circuit of the present invention. 3A-3C are schematic diagrams showing the structure of three different pixel units of the fingerprint sensing device of the present invention. 4A is a graph showing the relationship between the output voltage value of the fingerprint sensing circuit and the coupling capacitance value of the present invention. Figure 4B: Waveform of a noise. FIG. 5A is a schematic structural view of a fingerprint sensing device. Fig. 5B is an enlarged view showing a part of the structure of Fig. 5A. FIG. 5C is a schematic diagram of a partial structure (side view) and a fingerprint sensing circuit of FIG. 5A. 6A and 6B are schematic diagrams showing the operation of the driving and receiving circuits of the fingerprint sensing circuit. Fig. 7A is a graph showing the relationship between the output voltage value of the fingerprint detecting circuit and the coupling capacitance value. Fig. 7B is a waveform diagram of a noise.

10‧‧‧Substrate

11‧‧‧Pixel unit

111‧‧‧First electrode section

112‧‧‧Second electrode

Claims (11)

A fingerprint sensing device includes: a substrate; a plurality of pixel units corresponding to one side of the substrate, each of the pixel units including a first electrode portion and a second electrode portion; and a fingerprint sensing circuit Connecting to the plurality of pixel units, comprising: a plurality of driving units respectively connected to the pixel units, each driving unit being connected to the first and second electrode portions of the corresponding pixel unit, driving the first driving voltage The first electrode portion drives the second electrode portion with a second driving voltage, the first driving voltage is different from the second driving voltage; and the plurality of sensing units are respectively connected to the pixel unit to receive corresponding a first capacitive sensing signal of the first electrode portion and a second capacitive sensing signal of the second electrode portion in the pixel unit, and performing operations according to the first and second capacitive sensing signals to generate an output as the pixel unit The capacitance sensing information, wherein the capacitance sensing information of each of the pixel units is used to generate a fingerprint information. The fingerprint sensing device of claim 1, wherein each of the sensing units comprises: a differential circuit having an inverting input and a non-inverting input, the inverting input being through a first switch Connected to the corresponding first electrode portion, the non-inverting input terminal is connected to the corresponding second electrode portion through a second switch; a first reference voltage source is switchably connected to the inverting input terminal; And a second reference voltage source is switchably connected to the non-inverting input. The fingerprint sensing device of claim 2, wherein each of the driving units comprises: a first driving voltage source rotatably connected between the first switch and the first electrode portion to provide the first And driving a voltage; and a second driving voltage source is switchably connected between the second switch and the second electrode portion to provide the second driving voltage. The fingerprint sensing device of claim 3, wherein the voltages of the first reference voltage source and the second reference voltage source are the same. The fingerprint sensing device of claim 3, wherein the voltages of the second driving voltage source, the first reference voltage source, and the second reference voltage source are the same. The fingerprint sensing device according to any one of claims 2 to 5, wherein the plurality of pixel units and the fingerprint sensing circuit are integrated on the same wafer. The fingerprint sensing device of claim 1, wherein the first electrode portion and the second electrode portion of each pixel unit are in contact with the same portion of the finger, the total coupling between the first electrode portion and the finger portion The capacitance value is substantially the same as the total coupling capacitance value between the second electrode portion and the finger portion. The fingerprint sensing device of claim 7, wherein the first and second electrode portions have the same area. The fingerprint sensing device of claim 7, wherein each of the pixel electrode units includes a plurality of first and second electrode portions, the plurality of first and second electrode portions being the same in number and having the same area. The fingerprint sensing device of claim 9, wherein the plurality of first and second electrode portions in a first direction of each of the pixel units are staggered, and each of the pixel units is located in a second direction. The plurality of first and second electrode portions are staggered. The fingerprint sensing device of claim 9 or 10, wherein each of the pixel units further comprises at least one spare electrode, and the first and second electrode portions are arranged around the spare electrode.