CN101526990B - Capacitive fingerprint sensor and its panel - Google Patents

Abstract

The invention discloses a capacitive fingerprint sensor which comprises a fingerprint capacitor, an integrator, a first transistor, a second transistor and a multiplexer. The capacitance of the fingerprint capacitor is a concave capacitance C_FVOr a convex part capacitance value C_FRAnd C is_FV＜C_FR. The integrator has a reference capacitor C_fb. The first transistor is used for controlling the fingerprint capacitor in a scanning line period. The second transistor is used for pre-charging the fingerprint capacitor and redistributing charges between the fingerprint capacitor and the reference capacitor. The multiplexer is connected to the integrator to provide a first voltage VA and a second voltage VB, wherein the first voltage VA is greater than the second voltage VB.

Description

Capacitive fingerprint sensor and its panel

technical field

The invention relates to a capacitive fingerprint sensor and its panel, in particular to a capacitive fingerprint sensor using multiple transistors and its panel.

Background technique

A fingerprint sensor is a sensor used to recognize fingerprint patterns and provide reliable personal identification. The fingerprint sensor is also widely used in portable products, such as mobile phones and notebook computers, to ensure the security of personal confidential data.

Figures 1A and 1B show the equivalent circuit of a fingerprint sensor. In general, the fingerprint sensor can be implemented in a chip, and the numeral 13 in FIG. 1A represents a protective layer, which serves as a dielectric layer for the capacitor _Cd . If the fingerprint sensor is embedded in an image panel, number 11 in FIG. 1A represents an ITO layer, and number 13 represents glass and films, such as color filters, polarizers, and the like. The following description takes the fingerprint sensor embedded in the image panel as an example. In FIG. 1A , a glass 13 , an upper metal layer 11 and a substrate 12 are combined in series, and the glass 13 is a place that a user's fingers can touch. Usually a capacitance C _d exists in the glass 13 , and a capacitance C _P exists between the upper metal layer 11 and the substrate 12 . In FIG. 1B , the surface of the user's finger can be divided into a convex portion 14 and a concave portion 15 . The recess 15 and the glass 13 have a distance d2, while the glass 13 has a thickness d1. Based on this structure, an extra capacitance C2 exists between the recess of the user's finger and the surface of the glass 13 . The capacitance value C _FR of the convex part is related to C ₁ , the capacitance value C _FV of the concave part is related to C ₁ //C ₂ , and C ₁ and C ₁ //C ₂ can be expressed in the following way:

${\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="S2008100832619E00031.png,S2008100832619E00051.png"\; state="\{\{state\}\}">C</figure-callout>}}_1=\frac{{\mathrm{\&epsiv;}}_{1}A}{{\mathrm{<figure-callout\; id="1"\; label="d"\; filenames="S2008100832619E00031.png,S2008100832619E00051.png"\; state="\{\{state\}\}">d</figure-callout>}}_1},$ and ${\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="S2008100832619E00031.png,S2008100832619E00051.png"\; state="\{\{state\}\}">C</figure-callout>}}_1//C_2=\frac{1}{\frac{{\mathrm{<figure-callout\; id="1"\; label="d"\; filenames="S2008100832619E00031.png,S2008100832619E00051.png"\; state="\{\{state\}\}">d</figure-callout>}}_1}{{\mathrm{\&epsiv;}}_{1}A}+\frac{d_2}{{\mathrm{\&epsiv;}}_{2}A}}$

Usually, the convex portion capacitance C _FR is much larger than the concave portion capacitance C _FV .

In order to sense the user's finger, a readout circuit should be able to distinguish the capacitance value of the convex portion and the capacitance value of the concave portion. However, it is not easy to obtain the required accuracy because some environmental factors such as noise or crosstalk can detract from the result.

Contents of the invention

An embodiment of the capacitive fingerprint sensor of the present invention includes a sensing unit and a control circuit. The sensing unit includes a fingerprint capacitor and a first transistor. The capacitance value of the fingerprint capacitance is a concave portion capacitance C _FV or a convex portion capacitance C _FR , and C _FV <C _FR . The first transistor includes a gate terminal, an input terminal and an output terminal, wherein the gate terminal is controlled by a scanning line, and the input terminal is connected to the fingerprint capacitance, and the output terminal is connected to the readout line. The control circuit includes a second transistor, an operational amplifier, a reference capacitor, a third transistor and a multiplexer. The second transistor includes a gate terminal, an input terminal and an output terminal, wherein the gate terminal is controlled by a first reset line, and the input terminal is connected to the readout line. An input end of the operational amplifier is connected to an output end of the second transistor. The reference capacitor has a capacitance C _fb and is disposed between the input terminal and the output terminal of the operational amplifier. The third transistor includes a gate terminal, an input terminal and an output terminal, wherein the gate terminal is controlled by a second reset line, and the input terminal and the output terminal are respectively connected to the input terminal and the output terminal of the operational amplifier. The multiplexer is connected to another input terminal of the operational amplifier, wherein the input terminal of the multiplexer is connected to a first voltage VA and a second voltage VB.

Another embodiment of the capacitive fingerprint sensor of the present invention includes a fingerprint capacitor, an integrator, a first transistor, a second transistor and a multiplexer. The capacitance value of the fingerprint capacitance is a concave portion capacitance C _FV or a convex portion capacitance C _FR , and C _FV <C _FR . The integrator has a reference capacitor C _fb . The first transistor is used to control the fingerprint capacitance in a scan line period. The second transistor is used to precharge the fingerprint capacitor and redistribute charge between the fingerprint capacitor and a reference capacitor. The multiplexer is connected to the integrator to provide a first voltage VA and a second voltage VB, wherein the first voltage VA is greater than the second voltage VB.

An embodiment of the panel system including a capacitive fingerprint sensor of the present invention includes an active matrix area with a plurality of capacitive fingerprint sensing units, a data driver, a scan driver, a readout circuit and an image processing circuit. The data driver is used to drive data. The scan driver is used to control the scan lines connected to the capacitive fingerprint sensor. The readout circuit is used for receiving the data of the capacitive fingerprint sensor and identifying the type of the fingerprint capacitance. The image processing circuit is connected to the readout circuit.

Description of drawings

Figure 1A and 1B show the equivalent circuit of the fingerprint sensor;

Figure 2 shows a specific embodiment of the panel of the present invention;

Fig. 3 shows a specific embodiment of the fingerprint sensor of the present invention;

Fig. 4 shows the timing diagram of the circuit of Fig. 3;

5A to 5C show the precharge phase, conversion phase and evaluation phase of the circuit of FIG. 3; and

FIG. 6 shows a portion of a readout circuit of an embodiment of the present invention.

Description of reference symbols

11 upper metal plate 12 substrate

13 Protective layer 14 Fingerprint convex part

15 fingerprint recess

21 data driver 22 scan driver

23 readout circuit 24 image processing circuit

25 panels

31 capacitive fingerprint sensing unit 32 first transistor

33 fingerprint capacitance 34 second transistor

35 third transistor 36 operational amplifier

37 multiplexer 38 control circuit

61 comparators 62 multiplexers

C _fb reference capacitance

Detailed ways

Figure 2 shows a specific embodiment of the panel of the present invention. The panel system includes an active matrix area 25 , a data driver 21 , a scan driver 22 , a readout circuit 23 and an image processing circuit 24 . The active matrix area 25 includes a capacitive fingerprint sensor and/or a plurality of image pixels. The capacitive fingerprint sensor has a plurality of capacitive fingerprint sensing units 31 , and each capacitive fingerprint sensing unit 31 can selectively coexist with an image pixel in a pixel unit. The data driver 21 is used to drive data. The scan driver 22 is used to control the scan lines connected to the capacitive fingerprint sensing unit 31 . Generally speaking, when the capacitive fingerprint sensing unit 31 is operated, the scanning lines connected to the capacitive fingerprint sensing unit 31 are activated during the whole operation process. The readout circuit 23 is used for receiving the analog signal of the readout line of the capacitive fingerprint sensing unit 31, and identifying the type of the fingerprint capacitor 31, such as the concave portion capacitance C _FV or the convex portion capacitance C _FR . The image processing circuit 24 is connected to the readout circuit 23 . The structure in FIG. 2 is an example of an embedded structure of an image panel, but those skilled in the art know that the structure in FIG. 2 can be easily converted and applied in a chip.

FIG. 3 shows a specific embodiment of the fingerprint sensor of the present invention. The readout circuit 23 includes a control circuit 38 . The capacitive fingerprint sensing unit 31 includes a first transistor 32 and a fingerprint capacitance C _F , the capacitance of which is a concave capacitance C _FV or a convex capacitance C _FR , and C _FV <C _FR . The first transistors in the same column of the active matrix region 25 are controlled by the same scan line. The first transistor 32 includes a gate terminal, an input terminal and an output terminal, wherein the gate terminal is controlled by a scan line, and the input terminal is connected to the fingerprint capacitor, and the output terminal is connected to a readout line, wherein The readout line is also connected to an input terminal of the control circuit 38 . The control circuit 38 may be part of the readout circuit 23, another part 61 is shown in FIG. 6 . The control circuit 38 includes a second transistor 34 , an operational amplifier 36 , a reference capacitor C _fb , a third transistor 35 and a multiplexer 37 , wherein the operational amplifier 36 and the reference capacitor C _fb serve as an integrator. The second transistor 34 includes a gate terminal, an input terminal and an output terminal, wherein the gate terminal is controlled by a first reset line Reset1, and the input terminal is connected to the readout line. An input terminal of the operational amplifier 36 is connected to an output terminal of the second transistor 34 . The reference capacitor C _fb is connected to the input terminal and the output terminal of the operational amplifier 36 . The third transistor 35 includes a gate terminal, an input terminal and an output terminal, wherein the gate terminal is controlled by a second reset line Reset, and the input terminal and the output terminal are connected to the input terminal and the output terminal of the operational amplifier 36 end. The multiplexer 37 is connected to the other input terminal of the operational amplifier 36 , wherein the input terminal of the multiplexer is connected to a first voltage VA and a second voltage VB. In this embodiment, the first voltage VA is greater than the second voltage VB.

Figure 4 shows the timing diagram for the circuit of Figure 3. Generally speaking, the fingerprint capacitors in the same column share the same scan line _Rn , which is activated during the entire operation of all the fingerprint capacitors in the column. The timing of one cycle is divided into a pre-charging phase (first phase), a conversion phase (second phase) and an estimation phase (third phase), and they do not overlap with each other. The first reset line Reset1 is activated during the pre-charging phase and the evaluation phase, and the second reset line Reset is activated during the pre-charging phase and the conversion phase. During the evaluation stage, the readout line selection RLS sequentially transmits data from Vout ₁ to Vout _x to the image processing circuit 24 .

Figure 5A shows the equivalent circuit of the fingerprint sensor in the pre-charging stage. In the pre-charge phase, the second transistor 34 and the third transistor 35 are enabled, and the multiplexer 36 selects VB. Accordingly, the reference capacitor C _fb is reset, and the second voltage VB is input to the fingerprint capacitor. At this time, the charge stored in the fingerprint capacitor is C _F ×VB.

Figure 5B shows the equivalent circuit of the fingerprint sensor during the switching phase. In the switching phase, the second transistor 34 is turned off, the third transistor 35 is enabled, and the multiplexer 36 selects VA so that the operational amplifier 36 outputs VA.

FIG. 5C shows the equivalent circuit of the fingerprint sensor in the evaluation phase. During the evaluation phase, the second transistor 34 is enabled, the third transistor 35 is turned off, and the multiplexer 36 still selects VA. At this time, the charge stored in the fingerprint capacitor is redistributed to the reference capacitor C _fb , and the operational amplifier 36 changes its output according to the detected part of the user's finger, that is, the convex part or the concave part of the fingerprint. $\mathrm{VA}+\frac{(\mathrm{VA}-\mathrm{VB})\&times;C_{\mathrm{FR}}}{C_{\mathrm{fb}}}$ or $\mathrm{VA}+\frac{(\mathrm{VA}-\mathrm{VB})\&times;C_{\mathrm{FV}}}{C_{\mathrm{fb}}}$

FIG. 6 shows a portion of a readout circuit of an embodiment of the present invention. The readout circuit 23 also includes a multiplexer 62 and a comparator 61 . The selection part 63 receives data from Vout ₁ to Vout _x and sends it to the image processing circuit 24 . The input of the multiplexer 62 is connected to the data selected by Vout ₁ to Vout _x , and the output of the multiplexer 62 is connected to the comparator 61 . The comparator 61 outputs a bit to the image processing circuit 24 . In order to distinguish the capacitance of the convex portion and the capacitance of the concave portion, the comparator 61 uses a threshold voltage V _REF , and $\mathrm{VA}+\frac{(\mathrm{VA}-\mathrm{VB})\&times;C_{\mathrm{FR}}}{C_{\mathrm{fb}}}>V_{\mathrm{REF}}>\mathrm{VA}+\frac{(\mathrm{VA}-\mathrm{VB})\&times;C_{\mathrm{FV}}}{C_{\mathrm{fb}}}.$ Accordingly, if the comparator 61 outputs a logic high level, it means that the data received by the fingerprint sensor is the bump capacitance. On the contrary, it is the recess capacitance.

The technical content and technical features of the present invention have been disclosed above, but those skilled in the art may still make various substitutions and modifications based on the teaching and disclosure of the present invention without departing from the spirit of the present invention. Therefore, the protection scope of the present invention should not be limited to those disclosed in the embodiments, but should include various replacements and modifications that do not deviate from the present invention, and are covered by the claims of the present invention.

Claims (6)

1. capacitance-typed fingerprint sensor comprises:

One sensing unit comprises:

One fingerprint capacitor, its capacitance are a recess capacitance C _FVAn or protuberance capacitance C _FR, and C _FV＜C _FRAnd

One the first transistor comprises a gate terminal, an input end and an output terminal, and wherein this gate terminal is controlled by the one scan line, and this input end is connected to an end of this fingerprint capacitor, the other end ground connection of this fingerprint capacitor, and this output terminal is connected to this sense wire; And

One control circuit comprises:

One transistor seconds comprises a gate terminal, an input end and an output terminal, and wherein this gate terminal is controlled by one first replacement line, and this input end is connected to this sense wire;

One operational amplifier, its first input end is connected to the output terminal of this transistor seconds;

One reference capacitance has a capacitance C _Fb, and be arranged between the first input end and output terminal of this operational amplifier;

One the 3rd transistor comprises a gate terminal, an input end and an output terminal, and wherein this gate terminal is controlled by one second replacement line, and this input end and output terminal are connected to the first input end and the output terminal of this operational amplifier respectively; And

One multiplexer, its output terminal are connected to second input end of this operational amplifier, and wherein the input end of this multiplexer is connected to one first voltage VA and one second voltage VB, and wherein this first voltage VA is greater than this second voltage VB.

2. capacitance-typed fingerprint sensor as claimed in claim 1, its operation serial word be in a pre-charging stage, a translate phase and an estimating stage,

Wherein in this pre-charging stage, this sweep trace, the first replacement line and the second replacement line are activated, and this multiplexer exports this second voltage VB,

Wherein at this translate phase, this sweep trace and the second replacement line are activated, and this first replacement line is not activated, and this multiplexer exports this first voltage VA,

Wherein in this estimating stage, this sweep trace and the first replacement line are activated, and this second replacement line is not activated, and this multiplexer is exported this first voltage VA.

3. panel system that comprises capacitance-typed fingerprint sensor comprises:

One has the active-matrix zone of a plurality of capacitance type fingerprint sensing units, and respectively this capacitance type fingerprint sensing unit comprises:

One fingerprint capacitor, its capacitance are a recess capacitance C _FVAn or protuberance capacitance C _FR, and C _FV＜C _FRAnd

One the first transistor comprises a gate terminal, an input end and an output terminal, and wherein this gate terminal is controlled by the one scan line, and this input end is connected to an end of this fingerprint capacitor, the other end ground connection of this fingerprint capacitor, and this output terminal is connected to this sense wire;

The one scan driver is used to control described sweep trace;

One sensing circuit comprises:

One transistor seconds comprises a gate terminal, an input end and an output terminal, and wherein this gate terminal is controlled by one first replacement line, and this input end is connected to this sense wire;

One operational amplifier, its first input end is connected to the output terminal of this transistor seconds;

One reference capacitance has a capacitance C _Fb, and be arranged between the first input end and output terminal of this operational amplifier;

One the 3rd transistor comprises a gate terminal, an input end and an output terminal, and wherein this gate terminal is controlled by one second replacement line, and this input end and output terminal are connected to the first input end and the output terminal of this operational amplifier respectively; And

One multiplexer, its output terminal are connected to second input end of this operational amplifier, and wherein the input end of this multiplexer is connected to one first voltage VA and one second voltage VB, and wherein this first voltage VA is greater than this second voltage VB; And

One image-processing circuit is connected to this sensing circuit,

Wherein this sensing circuit also comprises an output multiplexer and a comparer, the input end of this output multiplexer is connected to the output terminal of this operational amplifier, the output terminal of this output multiplexer is connected to an input end of this comparer, and another input end of this comparer is connected to a threshold voltage V _REF, the output terminal of this comparer is connected to this image-processing circuit.

4. panel system as claimed in claim 3, wherein this comparer is exported one to this image-processing circuit.

5. panel system as claimed in claim 3, wherein

6. panel system as claimed in claim 3, wherein when this capacitance type fingerprint sensing unit was operated, the one scan line that is connected to this capacitance type fingerprint sensing unit was activated.

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