Detection circuit and terminal device

Abstract

The utility model provides a detection circuit and a terminal device, the detection circuit comprises a buffer circuit, a switch unit and sampling units, the switch unit adjusts at least two sampling units to be connected in parallel between an output end and a voltage reference end of a fingerprint sensing unit; therefore, the at least two sampling units can synchronously collect and store the fingerprint echo signals output by the fingerprint sensing unit, so that the total signal capacity value of the sampling units can be improved, and the sampling amount of the fingerprint echo signals is increased; and then the switch unit adjusts the at least two sampling units to be connected in series between the input end and the voltage reference end of the buffer circuit, so that the at least two sampling units output the stored fingerprint echo signal to the buffer circuit to amplify the fingerprint echo signal. Therefore, the sampling noise can be reduced, and the signal-to-noise ratio can be improved.

Description

Technical Field

[0001] The utility model relates to the technical field of integrated circuits, in particular to a detection circuit and terminal equipment. Background Art

[0002] Fingerprints are the uneven, uneven patterns on the surface of a finger. They are unique, heritable, and immutable. Fingerprint repetition rates are extremely low, making it possible to authenticate a person's identity by collecting fingerprint signals. In related ultrasonic fingerprint detection technology, the input fingerprint signal is generated in response to ultrasonic waves that are reflected from the object to be imaged and propagated through a piezoelectric layer. In practical applications, the echo signal reflected back by the ultrasonic waves is small, resulting in a low signal-to-noise ratio (SNR), resulting in low fingerprint detection accuracy. Utility Model Content

[0003] The purpose of the utility model is to provide a fingerprint detection circuit and terminal equipment to solve the problem that the signal-to-noise ratio of the echo signal reflected by the ultrasonic wave in the current ultrasonic fingerprint detection technology is low, resulting in low accuracy of fingerprint detection.

[0004] In order to solve the above technical problems, based on one aspect of the present utility model, the present utility model provides a detection circuit, which includes a buffer circuit, a switch unit and a sampling unit;

[0005] The switch unit adjusts at least two of the sampling units to be connected in parallel between the output terminal of the fingerprint sensing unit and the voltage reference terminal, so as to synchronously collect and store the fingerprint echo signal output by the fingerprint sensing unit;

[0006] Alternatively, the switch unit adjusts at least two of the sampling units to be connected in series between the input terminal of the buffer circuit and the voltage reference terminal, so as to output the fingerprint echo signal to the buffer circuit.

[0007] Optionally, the switching unit includes a first switch, a second switch and a third switch corresponding to the sampling unit, the first end of the first switch is connected to the fingerprint sensing unit, and the second end of the first switch is connected to the buffer circuit through a signal bus; after the sampling unit is connected to the corresponding third switch, it is connected between the signal bus and the voltage reference end, and the two adjacent sampling units are connected at both ends of the second switch.

[0008] Optionally, when the first switch is turned on, the second switch is turned off, and the third switch is turned on, at least two of the sampling units are connected in parallel between the output end of the fingerprint sensing unit and the voltage reference end; when the first switch is turned off, the second switch is turned on, and the third switch is turned off, at least two of the sampling units are connected in series between the input end of the buffer circuit and the voltage reference end.

[0009] Optionally, the switch unit is further configured to reset the sampling unit; and the switch unit first resets the sampling unit, then adjusts at least two of the sampling units to be connected in parallel, and then adjusts at least two of the sampling units to be connected in series.

[0010] Optionally, the switch unit includes a fourth switch, one end of the sampling unit is connected to the voltage reference end through the fourth switch, and the other end of the sampling unit is coupled to the voltage reference end.

[0011] Optionally, the sampling unit includes a sampling capacitor.

[0012] Optionally, the capacitances of at least two of the sampling capacitors are equal.

[0013] Optionally, the buffer circuit includes an operational amplifier, the switch unit adjusts at least two sampling units to be connected in series and then connected to a first input terminal of the operational amplifier, and the second input terminal of the operational amplifier is connected to an output terminal of the operational amplifier.

[0014] Based on another aspect of the present invention, the present invention further provides a terminal device, which includes a fingerprint sensing unit and the detection circuit as described above.

[0015] Optionally, the fingerprint sensing unit includes an ultrasonic sensing unit or a piezoelectric sensing unit.

[0016] Optionally, the terminal device further includes a reading circuit, and the reading circuit is connected to the output end of the buffer circuit through a fifth switch.

[0017] The detection circuit described above first adjusts at least two sampling units in parallel between the output terminal of the fingerprint sensing unit and the voltage reference terminal through a switch unit, so that the at least two sampling units can synchronously collect and store the fingerprint echo signal output by the fingerprint sensing unit. This can increase the total signal capacity value of the sampling unit, increase the sampling amount of the fingerprint echo signal, and stack and amplify the fingerprint echo signal. Then, the at least two sampling units are adjusted in series between the input terminal and the voltage reference terminal of the buffer circuit through a switch unit, so that the at least two sampling units output the stacked and amplified fingerprint echo signal to the buffer circuit. In this way, the present invention can amplify the collected fingerprint echo signal and improve the signal-to-noise ratio by sampling the fingerprint echo signal in a mode in which at least two sampling units are connected in parallel and outputting the fingerprint echo signal to the buffer circuit in a mode in which at least two sampling units are connected in series.

[0018] It should be noted that, since the terminal device includes the detection circuit, it also has the technical effects brought by the detection circuit, which will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Those skilled in the art will appreciate that the accompanying drawings are provided to better understand the present invention and do not constitute any limitation on the scope of the present invention.

[0020] Figure 1 This is a schematic diagram of a detection circuit in the related art;

[0021] Figure 2 1 is a schematic diagram of a detection circuit according to an embodiment of the present invention;

[0022] Figure 3 This is another schematic diagram of a detection circuit according to an embodiment of the present invention;

[0023] Figure 4 This is another schematic diagram of a detection circuit according to an embodiment of the present invention;

[0024] Figure 5 This is a timing diagram of the first switch, the second switch, the third switch, the fourth switch, and the fifth switch according to an embodiment of the present invention.

[0025] In the attached figure:

[0026] 10- fingerprint sensing unit; 20- reading circuit; 30- buffer circuit;

[0027] Q1 - first controllable switch; Q2 - second controllable switch; Q3 - third controllable switch; S1 - first switch; S2 - second switch; S3 - third switch; S4 - fourth switch; S5 - fifth switch; C0 - capacitor; C - sampling unit; C1 - first sampling unit; C2 - second sampling unit. DETAILED DESCRIPTION

[0028] To further clarify the objectives, advantages, and features of the present invention, the present invention is further described below in conjunction with the accompanying drawings and specific embodiments. It should be noted that the drawings are highly simplified and not drawn to scale, and are intended solely to facilitate and clearly illustrate the objectives of the embodiments of the present invention. Furthermore, the structures shown in the drawings are often portions of the actual structures. In particular, different drawings may require different emphases and may use different scales.

[0029] As used in the present invention, the singular forms "a", "an", and "the" include plural referents, the term "or" is generally used to include "and / or", the term "several" is generally used to include "at least one", and the term "at least two" is generally used to include "two or more". In addition, the terms "first", "second", and "third" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features specified as "first", "second", and "third" may explicitly or implicitly include one or at least two of the features, "one end" and "the other end" and "proximal end" and "distal end" generally refer to two corresponding parts, which not only include endpoints, and the terms "mounted", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal communication between two elements or the interaction relationship between two elements. In addition, as used in this utility model, "one element is disposed on another element" generally only indicates that there is a connection, coupling, cooperation, or transmission relationship between the two elements, and the connection, coupling, cooperation, or transmission between the two elements can be direct or indirect through an intermediate element, and should not be understood as indicating or implying a spatial positional relationship between the two elements, that is, one element can be in any orientation such as inside, outside, above, below, or to the side of another element, unless otherwise explicitly stated. For those skilled in the art, the specific meanings of the above terms in this utility model can be understood according to specific circumstances.

[0030] like Figure 1 In the detector circuit shown in the related art, the signal output by the fingerprint sensing unit 10 is generated by the echo signal sensed by the piezoelectric layer of the piezoelectric sensor within the fingerprint sensing unit 10 after being reflected by the object to be imaged. Vech is the equivalent voltage caused by the echo of the ultrasonic reflection, which can be considered as the fingerprint-representing signal (i.e., the fingerprint echo signal) output by the fingerprint sensing unit 10. The reading circuit 20 is used to read and quantize the fingerprint echo signal after being processed by the operational amplifier. The above detection circuit has three working stages, namely, a reset stage, a sampling stage, and a reading stage. In the reset stage, the first controllable switch Q1 and the second controllable switch Q2 are both turned on, and the third controllable switch Q3 is turned off, so as to discharge the capacitor C0 and clear the charge on the capacitor C0. In the sampling stage, the first controllable switch Q1 and the third controllable switch Q3 are both turned off, and the second controllable switch Q2 is turned on, so as to sample the fingerprint echo signal output by the fingerprint sensing unit 10 through the capacitor C0. In the reading stage, the first controllable switch Q1 and the second controllable switch Q2 are both turned off, and the third controllable switch Q3 is turned on, so that the reading circuit 20 reads and quantizes the fingerprint echo signal processed by the operational amplifier A.

[0031] Ideally, the sampling gain is:

[0032]

[0033] Among them, V Fi Characterizes the fingerprint echo signal output by capacitor C0 to op amp A, C in Characterizes the equivalent capacitance of the piezoelectric sensor of the fingerprint sensing unit 10, where C s Characterizes the capacitance value of capacitor C0.

[0034] It is understandable that the gain of op amp A is VFo / V Fi , where V Fo is the fingerprint echo signal after being processed by the operational amplifier.

[0035] The detection circuit in the related art has a small signal sampling gain and a low signal-to-noise ratio, which is not conducive to improving the accuracy of fingerprint recognition.

[0036] In view of this, the present invention provides a new fingerprint detection circuit to solve the problem in the current ultrasonic fingerprint detection technology that the signal-to-noise ratio of the echo signal reflected by the ultrasonic wave is low, resulting in low accuracy of fingerprint detection.

[0037] See Figure 2 and Figure 3 This embodiment provides a detection circuit for a terminal device. The detection circuit includes a buffer circuit 30, a switch unit (S1, S2, S3, S4) and a sampling unit C. The number of sampling units C is at least two. The sampling unit C can collect and store the fingerprint echo signal output by the fingerprint sensing unit 10. The buffer circuit 30 can be a unit gain buffer circuit. After buffering the fingerprint echo signal, it is output to the reading circuit 20 so that the reading circuit 20 can read and quantify the fingerprint echo signal. The fingerprint sensing unit 10 here can refer to Figure 1The fingerprint sensing unit 10 in the embodiment can be further understood as comprising, for example, a piezoelectric sensor having an ultrasonic wave sensing array. A fingerprint echo signal is generated in response to ultrasonic waves reflected from an object to be imaged and sensed by the piezoelectric layer of the piezoelectric sensor. The sampling unit C can selectively connect to a pixel unit of the ultrasonic wave sensing array to acquire the fingerprint echo signal. In other embodiments, the fingerprint sensing unit 10 comprises an ultrasonic sensing unit or a piezoelectric sensing unit. The switching unit can adjust at least two sampling units C to be connected in parallel between the output terminal of the fingerprint sensing unit 10 and the voltage reference terminal VDB to synchronously collect and store the fingerprint echo signal output by the fingerprint sensing unit 10. The switching unit is further configured to adjust at least two sampling units C to be connected in series between the input terminal of the buffer circuit 30 and the voltage reference terminal VDB to output the fingerprint echo signal to the buffer circuit 30. The voltage reference terminal VDB herein can be a circuit node within the terminal device that provides a bandgap reference voltage for a chip, or it can be a reference ground.

[0038] Thus, the present invention can first adjust the at least two sampling units C to be connected in parallel between the output terminal of the fingerprint sensing unit 10 and the voltage reference terminal VDB through the switch unit, so that the at least two sampling units C can synchronously collect and store the fingerprint echo signal output by the fingerprint sensing unit 10. This can increase the total signal capacity of the sampling units C, increase the sampling amount of the fingerprint echo signal, and stack and amplify the fingerprint echo signal. Then, the at least two sampling units C can be adjusted to be connected in series between the input terminal of the buffer circuit 30 and the voltage reference terminal VDB through the switch unit, so that the at least two sampling units C output the stacked and amplified fingerprint echo signal to the buffer circuit 30. In this way, the present invention can amplify the collected fingerprint echo signal and improve the signal-to-noise ratio by sampling the fingerprint echo signal in a parallel mode with at least two sampling units C and outputting the fingerprint echo signal to the buffer circuit 30 in a series mode with at least two sampling units C.

[0039] As an example, the sampling unit C can be a sampling capacitor. Optionally, the capacitance of at least two sampling units C is equal. Those skilled in the art will appreciate that when at least two sampling units C are connected in parallel, the total capacitance of the sampling units C increases, thereby increasing the storage capacity of the charge pump, thereby increasing the sampling capacity of the fingerprint echo signal, and reducing sampling noise.

[0040] Ideally, the sampling gain of the detection circuit of this embodiment is:

[0041]

[0042] Among them, V Fi Characterizes the fingerprint echo signal output by at least two sampling units C to the buffer circuit 30, C in Characterizes the equivalent capacitance of the piezoelectric sensor of the fingerprint sensing unit 10, where Cs Characterizes the capacitance value when at least two sampling units C are connected in parallel, that is, C s =C1+C2+……+C n , n is the number of sampling units C connected in parallel.

[0043] As an example, the buffer circuit 30 includes an operational amplifier, the switch unit adjusts at least two sampling units C to be connected in series and then connected to the first input terminal (such as the non-inverting input terminal) of the operational amplifier, and the second input terminal (the inverting input terminal) of the operational amplifier is connected to the output terminal of the operational amplifier. For example, see Figure 4 , the operational amplifier can be configured based on the principle of MOS tube common source amplification.

[0044] Continue reading Figure 2 and Figure 3 The switch unit includes a first switch S1, a second switch S2, and a third switch S3 corresponding to each sampling unit C. The first end of the first switch S1 is connected to the output of the fingerprint sensing unit 10, and the second end of the first switch S1 is connected to the first input of the buffer circuit 30 via the signal bus. The sampling units C are connected to the corresponding third switches S3 and connected between the signal bus and the voltage reference terminal VDB. Two adjacent sampling units C are connected across the second switch S2. Thus, when the first switch S1 is on, the second switch S2 is off, and the third switch S3 is on, at least two sampling units C are connected in parallel between the output of the fingerprint sensing unit 10 and the voltage reference terminal VDB. When the first switch S1 is off, the second switch S2 is on, and the third switch S3 is off, at least two sampling units C are connected in series between the input of the buffer circuit 30 and the voltage reference terminal VDB.

[0045] For example, see Figure 2 For example, two sampling units C are described, namely, a first sampling unit C1 and a second sampling unit C2. The first end of the first sampling unit C1 is connected to the signal bus, and the second end of the first sampling unit C1 is connected to the voltage reference terminal VDB via a corresponding third switch S3. The first end of the second sampling unit C2 is connected to the signal bus, and the second end of the second sampling unit C2 is connected to the voltage reference terminal VDB via a corresponding third switch S3. The second end of the first sampling unit C1 is connected to the first end of the second sampling unit C2. Thus, when the first switch S1 is on, the second switch S2 is off, and the third switch S3 is on, the first sampling unit C1 and the second sampling unit C2 are connected in parallel between the output terminal of the fingerprint sensing unit 10 and the voltage reference terminal VDB. When the first switch S1 is off, the second switch S2 is on, and the third switch S3 is off, the first sampling unit C1 and the second sampling unit C2 are connected in series between the input terminal of the buffer circuit 30 and the voltage reference terminal VDB.

[0046] Furthermore, the switch unit is also used to reset the sampling unit C, thereby clearing the charge on the sampling unit C. For example, the switch unit adjusts both ends of the sampling unit C to be connected to the voltage reference terminal VDB. Furthermore, the switch unit first resets the sampling unit C, then adjusts at least two sampling units C to be connected in parallel, and then adjusts at least two sampling units C to be connected in series. In this way, by connecting both ends of the sampling unit C to the voltage reference terminal VDB, the charge on the sampling unit C is cleared. Then, at least two sampling units C are connected in parallel to collect fingerprint echo signals. Finally, the two sampling units C are connected in series to output the fingerprint echo signals to the buffer circuit 30.

[0047] For example, the switch unit further includes a fourth switch S4, one end of the sampling unit C is connected to the voltage reference terminal VDB through the fourth switch S4, and the other end of the sampling unit C is coupled to the voltage reference terminal VDB. When the fourth switch S4 is turned on, both ends of the sampling unit C are connected to the voltage reference terminal VDB. For example, see Figure 2 The first end of the fourth switch S4 is connected to the first end of the first switch S1, and the second end of the fourth switch S4 is connected to the voltage reference terminal VDB. In other embodiments, the first end of the fourth switch S4 may be connected to the signal bus, and the second end of the fourth switch S4 may be connected to the voltage reference terminal VDB.

[0048] Based on the above-described detection circuit, the present invention further provides a terminal device comprising a fingerprint sensing unit 10 and the above-described detection circuit. Furthermore, the terminal device further comprises a reading circuit 20 connected to the output of a buffer circuit 30 via a fifth switch S5 to read and quantify the fingerprint echo signal processed by the buffer circuit 30.

[0049] See Figure 2 and Figure 5 This embodiment illustrates the working stages of the detection circuit. The detection circuit of this embodiment has four working stages: a reset stage, a sampling stage, and an amplification and reading stage. During the reset stage, the fourth switch S4, the first switch S1, and the third switch S3 are all turned on, and the second switch S2 and the fifth switch S5 are all turned off, clearing the charge of the sampling unit C. During the sampling stage, the first switch S1 and the third switch S3 are all turned on, and the second switch S2, the fourth switch S4, and the fifth switch S5 are all turned off. At least two sampling units C are connected in parallel to sample and store the fingerprint echo signal. During the amplification and reading stage, the second switch S2 and the fifth switch S5 are all turned on, and the first switch S1, the third switch S3, and the fourth switch S4 are all turned off. At least two sampling units C are connected in series to output the fingerprint echo signal to the buffer circuit 30, and the buffer circuit 30 outputs the fingerprint echo signal to the reading circuit 20.

[0050] Although the present invention is disclosed above with reference to preferred embodiments, the above embodiments are not intended to limit the present invention. Any person skilled in the art can utilize the above-disclosed technical content to make many possible changes and modifications to the present invention without departing from the scope of the present invention, or to modify the present invention into equivalent embodiments with equivalent variations. Therefore, any simple modifications, equivalent variations, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the present invention are still within the scope of protection of the present invention.

Claims

1. A detection circuit, characterized in that: It includes a buffer circuit, a switch unit and a sampling unit; First, the switch unit is used to adjust at least two sampling units to be connected in parallel between the output terminal of the fingerprint sensing unit and the voltage reference terminal, so that the at least two sampling units connected in parallel synchronously collect and store the fingerprint echo signal output by the fingerprint sensing unit; Then, at least two sampling units are adjusted to be connected in series between the input end of the buffer circuit and the voltage reference end through the switch unit, so that the at least two sampling units connected in series output the fingerprint echo signal to the buffer circuit.

2. The detection circuit according to claim 1, wherein: The switching unit includes a first switch, a second switch, and a third switch corresponding to the sampling unit. The first end of the first switch is connected to the fingerprint sensing unit, and the second end of the first switch is connected to the buffer circuit through a signal bus. After the sampling unit is connected to the corresponding third switch, it is connected between the signal bus and the voltage reference terminal. Two adjacent sampling units are connected to the two ends of the second switch.

3. The detection circuit according to claim 2, wherein: When the first switch is turned on, the second switch is turned off, and the third switch is turned on, at least two of the sampling units are connected in parallel between the output end of the fingerprint sensing unit and the voltage reference end; when the first switch is turned off, the second switch is turned on, and the third switch is turned off, at least two of the sampling units are connected in series between the input end of the buffer circuit and the voltage reference end.

4. The detection circuit according to claim 1, wherein: The switch unit is further configured to reset the sampling unit; and the switch unit first resets the sampling unit, then adjusts at least two of the sampling units to be connected in parallel, and then adjusts at least two of the sampling units to be connected in series.

5. The detection circuit according to claim 4, wherein: The switch unit includes a fourth switch. One end of the sampling unit is connected to the voltage reference end through the fourth switch. The other end of the sampling unit is coupled to the voltage reference end.

6. The detection circuit according to claim 1, wherein: The sampling unit includes a sampling capacitor.

7. The detection circuit according to claim 6, wherein: The capacitance of at least two of the sampling capacitors is equal.

8. The detection circuit according to claim 1, wherein: The buffer circuit includes an operational amplifier, the switch unit adjusts at least two sampling units to be connected in series and then connected to a first input terminal of the operational amplifier, and the second input terminal of the operational amplifier is connected to an output terminal of the operational amplifier.

9. A terminal device, characterized in that: The invention comprises a fingerprint sensing unit and a detection circuit according to any one of claims 1 to 8.

10. The terminal device according to claim 9, characterized in that The fingerprint sensing unit includes an ultrasonic sensing unit or a piezoelectric sensing unit.

11. The terminal device according to claim 9, characterized in that The terminal device further includes a reading circuit connected to the output end of the buffer circuit through a fifth switch.

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