CN1577375A - Optical Fingerprint Detector with Variable Resistor - Google Patents

Abstract

A fingerprint sensor for recognizing a fingerprint includes an external signal detection processing circuit of a recognition unit and a plurality of recognition units. Each identification unit comprises a switch element, a first resistor and a second resistor. The switch element comprises a first end, a second end and a third end. The second resistor has a fixed resistance value. The fingerprint influences the intensity of light received by the first resistor, so that the resistance value of the first resistor is changed, and the potential of the second end is further changed. When the switch element is conducted, the external signal detection processing circuit of the identification unit identifies the fingerprint according to the electric potentials of the second ends of the switch elements.

Description

Optical Fingerprint Detector with Variable Resistor

technical field

The invention relates to a fingerprint detector, in particular to an optical fingerprint detector with variable resistance.

Background technique

Please refer to FIG. 1 , which is a functional block diagram of a conventional fingerprint detector 10 . The fingerprint detector 10 is a capacitive fingerprint sensor, which detects the change of the capacitance value to identify the fingerprint. The fingerprint detector 10 includes an identification unit external signal detection processing circuit 12 and a sensing area 14 . When a user wants to identify his fingerprint, he can press his finger on the sensing area 14, so that the relevant circuit in the sensing area 14 generates a corresponding signal according to the fingerprint of his finger, and then the sensing area 14 generates The signal will be transmitted to the external signal detection processing circuit 12 of the identification unit for analysis and processing, so as to identify the user's fingerprint.

Please refer to FIG. 2 , which is a circuit diagram of the sensing region 14 in FIG. 1 . The sensing area 14 includes a plurality of identification units 16 arranged in a matrix. Each identification unit 16 is used to sense the lines on the corresponding position on the user's fingerprint, and includes a transistor 18 and a detection capacitor Cf respectively. When the sensing area 14 is in operation, a detection signal Vs1 or Vs2 is applied to the source S of the transistor 18 , and when the user's fingerprint presses the surface of the sensing area 14 , the capacitance of the detection capacitor Cf will change. When the capacitance value of the detection capacitor Cf changes, the gate voltage of the transistor 18 will change due to the capacitive coupling effect, wherein the variation ΔVg of the gate voltage of the transistor 18 is determined by the capacitance value of the detection capacitor Cf, and can be expressed by the following equation express:

ΔVg＝Vs Cgs/(Cgs+Cf)

Wherein, Vs is the voltage value of the detection signal Vs1 or Vs2;

Cgs is the parasitic capacitance between the gate G and the source S of the transistor 18; and

Cf is the capacitance value of the detection capacitor.

The variation ΔVg of the gate voltage of the transistor 18 will directly affect the magnitude of the current I flowing through the transistor 18, and the external signal detection processing circuit 12 of the identification unit identifies the user's fingerprint according to the variation of the current I. However, the sensitivity of this fingerprint recognition method by detecting the change of the current I flowing through the transistor 18 is easily affected by the leakage current of the adjacent transistor 18, so that the recognition accuracy cannot be effectively improved.

Contents of the invention

Therefore, the object of the present invention is to provide a fingerprint detector for identifying fingerprints by detecting changes in potentials, so as to solve the above problems.

The fingerprint detector implemented according to the present invention includes an identification unit, an external signal detection processing circuit and a plurality of identification units. Each identifying unit includes a switch element, a first resistor, and a second resistor respectively. The switch element includes a first terminal, a second terminal and a third terminal, wherein the first terminal is connected to a starting terminal, the third terminal is connected to the external signal detection processing circuit of the identification unit, and the starting terminal is used to control The switching element is turned on and off. One end of the first resistor is connected to the second end of the switch element, and the detected fingerprint will affect the intensity of light received by the first resistor, so that the resistance value of the first resistor will change, and then the potential of the second end will be changed. Change. One end of the second resistor is connected to the second end of the switch element, and has a fixed resistance value. When the switch element is turned on, the identification unit external signal detection processing circuit will identify the fingerprint according to the potential of the second end of the switch element.

Description of drawings

FIG. 1 is a functional block diagram of a known capacitive fingerprint detector.

FIG. 2 is a circuit diagram of a sensing area of the fingerprint detector in FIG. 1 .

FIG. 3 is a functional block diagram of the resistive fingerprint detector of the present invention.

FIG. 4 is a schematic diagram of using the fingerprint detector in FIG. 3 to identify a fingerprint.

FIG. 5 is a circuit diagram of the sensing region in FIG. 3 .

Description of reference symbols

10, 50 Fingerprint detector 12, 52 External signal recognition unit

No. detection processing circuit

14, 54 Sensing area 16, 40 Identification unit

18, 56 Transistor 42 The first reference voltage terminal

44 Second reference voltage terminal 46 Start terminal

48 Output terminal 60 Translucent material

62 Fingerprint 64 Light

Detailed ways

Please refer to FIG. 3 , which is a functional block diagram of the resistive fingerprint detector 50 of the present invention. The fingerprint detector 50 is a resistive fingerprint sensor, which recognizes a fingerprint by detecting a voltage value changed due to a change in resistance value. The fingerprint detector 50 includes an identification unit external signal detection processing circuit 52 and a sensing area 54 . The sensing area 54 includes a plurality of identification units, and each identification unit includes a variable resistor, and the resistance value of the variable resistor changes due to the intensity of light received.

Please refer to FIG. 4 , which is a schematic diagram of using the fingerprint detector 50 in FIG. 3 to identify a fingerprint 62 . When it is desired to identify the fingerprint 62, the fingerprint 62 needs to be formed on a light-transmitting material 60 first, and then the light 64 is used to irradiate the light-transmitting material 60, so as to affect the illumination condition on the surface of the sensing area 54, thereby making the sensing area 54 more sensitive. The variable resistors of the plurality of identification units in the sensing area 54 can have relative resistance values due to the different illumination conditions. When the sensing area 54 is irradiated by the light 64, a plurality of identification units will output voltage signals corresponding to the resistance value of the variable resistor to the identification unit external signal detection processing circuit 52, and the identification unit external signal detection processing circuit 52 can The fingerprint 62 on the light-transmitting material 60 is identified through the received voltage signal.

Please refer to FIG. 5 , which is a circuit diagram of the sensing region 54 in FIG. 3 . The sensing area 54 includes a plurality of identification units 40, and each identification unit 40 is electrically connected to the first reference voltage terminal 42 and the second reference voltage terminal 44, and includes a first resistor R1, a second resistor R2, and a The switching element 56 is constituted by a transistor. The first resistor R1 and the second resistor R2 are electrically connected to the first reference voltage terminal 42 and the second reference voltage terminal 44 in series, wherein one end of the first resistor R1 is electrically connected to the first reference voltage terminal 42, and the second resistor Both terminals of R2 are electrically connected to the second reference voltage terminal 44 . The first resistor R1 is a photosensitive variable resistor, and its resistance value will show a corresponding change according to the intensity of the light it receives. The first resistor R1 can be made of amorphous silicon. When the light intensity received by the first resistor R1 is stronger, its resistance value will be lower, and vice versa. The resistance value of the second resistor R2 is fixed, and its resistance value will not change due to the intensity of light received, and the second resistor R2 can be made of indium tin oxide (ITO). In this embodiment, the transistor 56 is a metal oxide semiconductor (MOS) transistor, which includes a first terminal G that is a gate (gate), a second terminal that is a source (source), and a drain. The third end of the drain. The gate G of each transistor 56 is connected to a corresponding enabling terminal 46 , and the enabling terminal 46 can control whether the transistor 56 is turned on or not. Generally, when the start-up terminal 46 is in a floating state, the transistor 56 is non-conductive, but when a start-up voltage Vs1, Vs2, Vs3 or Vs4 is applied to the start-up terminal 46, a channel will be formed in the transistor 56 , so that the source S and the drain D are in a conduction state. Besides, the source S of the transistor 56 is connected to the first resistor R1 and the second resistor R2 , and its drain D is connected to a corresponding output terminal 48 .

When the light-transmitting material 60 is placed on the sensing area 54 to detect the fingerprint 62, the first reference voltage Vref1 will be applied to the first reference voltage terminal 42, and the second reference voltage Vref2 will be applied to the second reference voltage terminal 42. The voltage terminal 44, wherein the voltage value of the first reference voltage Vref1 is different from the voltage value of the second reference voltage Vref2. Therefore, the potential Vs of the source S of the transistor 56 can be expressed by the following equation:

$\mathrm{<span\; class="notranslate">\; vs.</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; Vref</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; [</span>\frac{\mathrm{<span\; class="notranslate">\; r</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; r</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; r</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; Vref</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; Vref</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; Vref</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; [</span>\frac{\mathrm{<span\; class="notranslate">\; r</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; r</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; r</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; Vref</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; Vref</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>$

Wherein, r1 is the resistance value of the first resistor R1, and r2 is the resistance value of the second resistor R2.

However, due to the influence of light 64 irradiation and fingerprint 62 shadowing, the resistance value of the first resistor R1 of each identification unit 40 will produce a corresponding change, wherein the resistance value of the first resistor R1 shadowed by the fingerprint 62 dark stripes will be higher. The resistance value of the first resistor R1 not covered by the stripes is large. Therefore, since the intensity of light received by each first resistor R1 will be affected by the stripes of the fingerprint 62 , the resistance value r1 of each first resistor R1 will show a corresponding change due to the difference in brightness and darkness of the fingerprint 62 . In addition, it can be seen from the above equation that the potential Vs of the source S of the transistor 56 is determined by the first reference voltage Vref1, the second reference voltage Vref2, and the resistance values r1 and r2. However, since the resistance value r2 is a fixed value, and the two reference The voltages Vref1 and Vref2 are also default values of the fingerprint detector 50, so the intensity of light received by the first resistor R1 can be determined according to the potential Vs of the source S, and therefore the potential Vs of the source S of each transistor 56 can be determined. It reflects the arrangement of the stripes of the fingerprint 62 . Therefore, the identification unit external signal detection processing circuit 52 can identify the fingerprint 62 according to the potential Vs of the sources S of the plurality of transistors 56 .

When the potential Vs of the source S of each transistor 56 changes due to the cover of the fingerprint 62, the external signal detection processing circuit 52 of the identification unit will apply a starting voltage Vs1, Vs2, Vs3 or Vs4 to each transistor 56 through each starting terminal 46 The gate G of , so that the corresponding transistor 56 is turned on. When the transistor 56 is turned on, the potential of the drain D of the turned-on transistor 56 will be affected by the potential of the source S to change. Therefore, the potential of the drain D of the transistor 56 in the on state can also reflect the arrangement of the stripes of the fingerprint 62 . In addition, the external signal detection processing circuit 52 of the identification unit can measure the potential of the drain D through the output terminal 48, and then analyze the stripe arrangement of the fingerprint 62 according to the measured potential of the drain D, so as to identify the fingerprint 62. the goal of. It should be noted that the potentials of the drains D of the transistors 56 interfere with each other, and at the same time, only the gates G of the transistors 56 in a single column are applied with the start-up voltage.

Compared with the known capacitive fingerprint detector, the resistive fingerprint detector of the present invention includes an identification unit, an external signal detection processing circuit and a plurality of identification units. Each identifying unit includes a switch element, a variable resistor, and a resistor with a fixed resistance value. The resistance value of the variable resistor will change due to the intensity of light received, so that an output potential of the switch element will be affected by the light level of the variable resistor, and the external signal detection processing circuit of the identification unit can be By measuring the output potential to identify the arrangement of the fingerprint lines. In addition, because the resistive fingerprint detector of the present invention recognizes fingerprints by detecting the output potential, there will be no problem of leakage current as known, and therefore the sensitivity and accuracy of the resistive fingerprint detector of the present invention are higher than those of known capacitors. Type fingerprint detector is preferred.

The above descriptions are only preferred embodiments of the present invention, and all equivalent changes and modifications made according to the claims of the present invention shall fall within the scope of the present invention.

Claims (5)

1. a fingerprint detector is used for discerning fingerprint, and this fingerprint detector includes:

One recognition unit external signal detects treatment circuit; And

Recognition unit, each recognition unit includes respectively:

One on-off element, it includes first end, second end and the 3rd end, and this first end is connected to a start end, and the 3rd end is connected to this recognition unit external signal and detects treatment circuit, and this start end is used for controlling the conducting and the shutoff of this on-off element;

First resistance, one end are connected to second end of described on-off element, and this fingerprint can influence the intensity of the suffered illumination of this first resistance, and the resistance value of this first resistance is changed, and then the current potential of this second end is changed; And

Second resistance, one end are connected to second end of described on-off element, and it has a fixing resistance value;

Wherein when described on-off element conducting, this recognition unit external signal detects treatment circuit can discern this fingerprint according to the current potential of second end of described on-off element.

2. fingerprint detector as claimed in claim 1, wherein an end of each recognition unit first resistance all is electrically connected to first reference voltage end, and an end of each recognition unit second resistance all is electrically connected to second reference voltage end, first reference voltage puts on this first reference voltage end, second reference voltage puts on this second reference voltage end, and the magnitude of voltage of this first reference voltage is different from the magnitude of voltage of this second reference voltage.

3. fingerprint detector as claimed in claim 1, wherein each on-off element is a transistor.

4. fingerprint detector as claimed in claim 1, wherein this first resistance is made by amorphous silicon.

5. fingerprint detector as claimed in claim 1, wherein this second resistance is made by tin indium oxide.

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