CN109889189B - Active load circuit based on fingerprint sensor acquisition array output stage - Google Patents
Active load circuit based on fingerprint sensor acquisition array output stage Download PDFInfo
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Abstract
The invention discloses an active load circuit based on a fingerprint sensor acquisition array output stage, which relates to the field of semiconductor chips and comprises a current source and an auxiliary discharging passage, wherein the auxiliary discharging passage is connected with the current source in parallel, one end of the auxiliary discharging passage is connected with a discharging node of the fingerprint sensor acquisition array, the other end of the auxiliary discharging passage is grounded, and the auxiliary discharging passage rapidly discharges the discharging node in a reset state of the fingerprint sensor acquisition array. According to the invention, by improving the active load circuit and adding the auxiliary discharging path on the basis of the current source, the charge discharging speed on the discharging node is improved, the resetting time of each acquisition point is shortened, the acquisition speed of the fingerprint image is improved, and the distortion degree of the image is reduced.
Description
Technical Field
The invention relates to the field of semiconductor chips, in particular to an active load circuit of a semiconductor fingerprint sensor acquisition array output stage.
Background
The existing semiconductor fingerprint sensor mostly consists of an acquisition array and a signal processing circuit. The fingerprint information is converted into analog voltage signals one by the acquisition array in a point-by-point scanning mode, and after the data of each point are received by an upper computer, the upper computer is spliced again according to the acquisition sequence through filtering, amplifying, analog-to-digital conversion and data transmission of a signal processing circuit, so that a gray level image representing the fingerprint information is obtained. The size of the acquisition array is also different according to the processing capacity, security level and related industry standards of different fingerprint algorithms, and the common acquisition array sizes are 160×160, 192×192, etc. In the acquisition array, each acquisition point is selectively controlled by a row address and a column address signal. The points with the row and column addresses enabled at the same time are selected for image acquisition. Each acquisition point comprises an independent output driving pipe, and the output driving pipes of all the acquisition points are finally converged together to form an output common node. Because of the large number of collection points in the collection array, the parasitic capacitance of the output driving tube and the output wires accumulated at a common node is large, the output driving tube can independently drive the capacitance, and an effective fingerprint small signal (a voltage signal of which the capacitance between the collection point and the finger fingerprint is directly converted, is small in amplitude and can be approximately a constant value in the range of signal change, and the post-stage circuit can be equivalent to a linear circuit relative to the signal change) is transmitted. The outputs of all output drive tubes share an active load whose primary function is to provide the necessary bias to the output drive tubes in the selected acquisition point (even though the circuit is at a quiescent operating voltage level at normal amplified state, around which the gain of the circuit is approximately constant), ensuring a normal bias of the output stage for each selected acquisition point in the reset state and the fingerprint acquisition state. Existing active load circuits are typically formed from a common current source. When the selected acquisition points are in a reset state, the current source discharges the common node, and as the common current source only can provide constant current bias, the charge discharge speed on the common node is limited, the reset time of each acquisition point is greatly prolonged, and the acquisition speed of the acquisition array is reduced. Let the charge on the array output common node be Q, the minimum discharge time tmin=q/I, I be the current bias. In the acquisition array, the physical position of each acquisition point is different, and the physical distance from the acquisition point to the active load is also different, so that the parasitic resistance and capacitance from each acquisition point to the active load are different, and the discharge speed of the active load to each selected acquisition point is also different. If enough reset time is not left, the acquisition point with large parasitic resistance and parasitic capacitance is far away from the public node, and the reset is insufficient, so that the small signal distortion of the acquired and output fingerprint is caused.
Therefore, those skilled in the art are dedicated to develop an active load circuit based on the output stage of the fingerprint sensor acquisition array, so as to achieve the purposes of improving the acquisition speed of fingerprint images and reducing the distortion degree of images.
Disclosure of Invention
In view of the above-mentioned drawbacks of the prior art, the present invention is to solve the technical problem of how to increase the acquisition speed of fingerprint images and reduce the distortion of images.
To achieve the above object, the inventors have studied and found that an existing active load circuit is usually formed of a common current source. When the selected acquisition point is in a reset state, the current source discharges the discharge node of the fingerprint sensor acquisition array, and as the common current source can only provide constant current bias, the charge discharge speed on the discharge node is limited, the reset time of each acquisition point is greatly prolonged, and the acquisition speed of the acquisition array is reduced. To increase the acquisition speed of fingerprint images, it is necessary to start with increasing the discharge speed of charges on the discharge nodes. The inventor considers adding auxiliary discharging paths on the basis of current sources to improve the discharging speed of charges on discharging nodes and shorten the reset time of each collecting point. Therefore, in a first embodiment of the present invention, an active load circuit based on an output stage of a fingerprint sensor acquisition array is provided, which includes a current source and an auxiliary discharge path, where the auxiliary discharge path is connected in parallel with the current source, one end of the auxiliary discharge path is connected to a discharge node of the fingerprint sensor acquisition array, and the other end of the auxiliary discharge path is grounded, and the auxiliary discharge path rapidly discharges the discharge node in a reset state of the fingerprint sensor acquisition array.
Optionally, in the active load circuit based on the fingerprint sensor acquisition array output stage in the foregoing embodiment, the current source includes a power source, a current source PMOS transistor and a current mirror, the current mirror includes a current mirror input NMOS transistor and a current mirror output NMOS transistor, a source of the current source PMOS transistor is connected to the power source, a gate of the current source PMOS transistor is connected to the bias voltage VBP, a drain of the current source PMOS transistor is connected to a drain of the current mirror input NMOS transistor, a gate of the current mirror input NMOS transistor is connected to a gate of the current mirror output NMOS transistor, a drain of the current mirror output NMOS transistor is connected to the discharge node, and sources of the current mirror input NMOS transistor and the current mirror output NMOS transistor are grounded.
In the second embodiment of the present invention, one structure of the auxiliary discharging path is a strong discharging path, which includes a strong discharging NMOS tube, a gate of the strong discharging NMOS tube is connected to a control signal, a source of the strong discharging NMOS tube is grounded, and a drain of the strong discharging NMOS tube is connected to a discharging node.
Further, in the active load circuit based on the fingerprint sensor acquisition array output stage in the above embodiment, the structure of the auxiliary discharging path enables the strong discharging path, that is, the control signal of the gate of the strong discharging NMOS tube becomes high level in the fingerprint sensor acquisition array reset state, and controls the strong discharging NMOS tube to be conducted, so that the strong discharging NMOS tube is in the triode region, and at this time, the strong discharging NMOS tube is equivalent to a small resistor, so that the charge of the discharging node is rapidly discharged to the ground through the strong discharging NMOS tube; before entering a fingerprint acquisition state (the latter half time of a reset state), the strong discharge channel is closed, namely, the control signal of the grid electrode of the strong discharge NMOS tube becomes low level, under the normal bias of the output NMOS tube of the current mirror, the output driving tube in the selected acquisition point of the fingerprint sensor acquisition array drives parasitic capacitance to quickly return to the normal bias state, and preparation is made for the fingerprint acquisition state of the next stage. It can be seen that this type of auxiliary discharge path, when the strong discharge path is enabled, produces a large transient current that can inject noise into the power and ground of the fingerprint sensor. However, the large transient current does not affect the normal use of the fingerprint acquisition sensor, but is a theoretical disadvantage.
In a third embodiment of the present invention, another improved structure of the auxiliary discharging path includes a virtual acquisition point (dummypixel), a virtual acquisition point output stage current source NMOS, an operational amplifier, and an auxiliary conduction NMOS, the virtual acquisition point (dummy pixel) is connected to the drain of the virtual acquisition point output stage current source NMOS and generates a reference voltage VREF, the reference voltage VREF is used as the inverting input of the operational amplifier, the forward input of the operational amplifier is connected to the discharging node, the output of the operational amplifier is connected to the gate of the auxiliary conduction NMOS, the drain of the auxiliary conduction NMOS is connected to the discharging node, the gate of the virtual acquisition point output stage current source NMOS is connected to the gate of the current mirror output NMOS, and the source of the virtual acquisition point output stage current source NMOS is grounded to the source of the auxiliary conduction NMOS.
Further, in the active load circuit based on the fingerprint sensor acquisition array output stage in the above embodiment, the auxiliary conduction NMOS is an N-type metal oxide semiconductor, the output of the operational amplifier controls the conduction state of the auxiliary conduction NMOS, specifically, the operational amplifier calculates the difference between the voltage of the discharge node and the reference voltage VREF, when the difference is greater than 0, the output voltage of the operational amplifier increases the conduction capacity of the auxiliary conduction NMOS, enhances the discharge capacity of the discharge node, and in response to the difference becoming smaller gradually, the output voltage of the operational amplifier decreases the conduction capacity of the auxiliary conduction NMOS, weakens the discharge capacity of the discharge node, and when the difference is equal to 0, the output driving tube of the acquisition point selected by the fingerprint sensor acquisition array enters a normal bias state.
In the fourth embodiment of the present invention, the auxiliary discharging path is further optimized, the current mirror output NMOS and the auxiliary conduction NMOS are combined into the power/conduction NMOS, and the switch is used for time-sharing switching control.
Further, in the active load circuit based on the fingerprint sensor acquisition array output stage in the above embodiment, the auxiliary discharging path includes a dummy acquisition point (dummy pixel), a dummy acquisition point output stage current source NMOS, an operational amplifier, an accelerated discharging switch, a normal bias switch, and a power/on NMOS, the dummy acquisition point (dummy pixel) and the drain of the dummy acquisition point output stage current source NMOS are connected and generate a reference voltage VREF, the reference voltage VREF is used as an inverting input of the operational amplifier, a forward input of the operational amplifier is connected to the discharging node, an output of the operational amplifier is connected to a gate of the power/on NMOS, a drain of the power/on NMOS is connected to the discharging node, the gate of the dummy acquisition point output stage current source NMOS is connected to a gate of the power/on NMOS, the source of the dummy acquisition point output stage current source NMOS is grounded, the accelerated discharging switch is disposed between the output of the operational amplifier and the gate of the power/on NMOS, and the normal bias switch is disposed between the gate of the dummy acquisition point output stage current source NMOS and the gate of the power/on NMOS.
Further, in the active load circuit based on the output stage of the fingerprint sensor acquisition array in the above embodiment, the time-sharing switching control of the switch means that when the acquisition point selected by the fingerprint sensor acquisition array enters a reset state, the accelerated discharge switch is closed, the normal bias switch is opened, the operational amplifier and the power/conduction NMOS form a negative feedback loop, the power/conduction NMOS serves as an auxiliary conduction NMOS, and the discharge node is rapidly discharged, so that the voltage of the discharge node is rapidly recovered to the reference voltage VREF; when the collection point selected by the fingerprint sensor collection array enters a fingerprint collection state, the accelerated discharge switch is opened, the normal bias switch is closed, the power supply/conduction NMOS tube serves as a current mirror output NMOS tube, and constant current bias is provided for the collection point selected by the fingerprint sensor collection array.
Optionally, in the active load circuit based on the output stage of the fingerprint sensor acquisition array in the third and fourth embodiments, a virtual acquisition point (dummy pixel) includes a virtual acquisition point proportional amplifying capacitor, a virtual acquisition point internal amplifying circuit, a virtual acquisition point row selection control tube, a virtual acquisition point column selection control tube, a virtual acquisition point output driving tube and a virtual acquisition point power supply, the virtual acquisition point proportional amplifying capacitor and the virtual acquisition point internal amplifying circuit are connected in parallel, two ends of the virtual acquisition point proportional amplifying capacitor are shorted, the virtual acquisition point internal amplifying circuit is connected with a gate of the virtual acquisition point output driving tube, a drain of the virtual acquisition point output driving tube is connected with the virtual acquisition point power supply, a source of the virtual acquisition point output driving tube is connected with a drain of the virtual acquisition point row selection control tube, a source of the virtual acquisition point row selection control tube is connected with a drain of the virtual acquisition point column selection control tube, a source of the virtual acquisition point column selection control tube is connected with a drain of the virtual acquisition point output stage NMOS, and the virtual acquisition point column selection control tube is connected with the virtual acquisition point selection tube and the virtual acquisition point column selection control tube is in a state of the virtual acquisition point column selection tube.
The invention provides a fingerprint sensor, which uses the active load circuit based on the fingerprint sensor acquisition array output stage in any embodiment.
The invention provides a circuit using the fingerprint sensor in the above embodiment.
According to the invention, by improving the active load circuit and adding the auxiliary discharging path on the basis of the current source, the charge discharging speed on the discharging node is improved, the resetting time of each acquisition point is shortened, the acquisition speed of the fingerprint image is improved, and the distortion degree of the image is reduced.
The conception, specific structure, and technical effects of the present invention will be further described with reference to the accompanying drawings to fully understand the objects, features, and effects of the present invention.
Drawings
FIG. 1 is a schematic diagram illustrating a conventional fingerprint sensor acquisition array and output according to an exemplary embodiment;
FIG. 2 is a schematic diagram illustrating a conventional active load circuit in accordance with an exemplary embodiment;
FIG. 3 is a schematic diagram illustrating an auxiliary discharge path according to an example embodiment;
FIG. 4 is a schematic diagram illustrating an auxiliary discharge path according to an example embodiment;
FIG. 5 is a schematic diagram illustrating an auxiliary discharge path according to an example embodiment;
FIG. 6 is a schematic diagram illustrating an auxiliary discharge path according to an example embodiment;
FIG. 7 is a schematic diagram illustrating a fingerprint sensor according to an example embodiment;
fig. 8 is a circuit schematic illustrating a circuit according to an exemplary embodiment.
Detailed Description
The following description of the preferred embodiments of the present invention refers to the accompanying drawings, which make the technical contents thereof more clear and easy to understand. The present invention may be embodied in many different forms of embodiments and the scope of the present invention is not limited to only the embodiments described herein.
In the drawings, like structural elements are referred to by like reference numerals and components having similar structure or function are referred to by like reference numerals. The dimensions and thickness of each component shown in the drawings are arbitrarily shown, and the present invention is not limited to the dimensions and thickness of each component. The thickness of the components is schematically and appropriately exaggerated in some places in the drawings for clarity of illustration.
In order to improve the acquisition speed of fingerprint images and reduce the distortion degree of the images, the inventor researches the circuit structures of the acquisition array and the output of the conventional fingerprint sensor and the working process of an acquisition point circuit in the fingerprint acquisition process. Fig. 1 is a schematic diagram of a conventional fingerprint sensor array acquisition and output, where the conventional fingerprint sensor 100 includes a single acquisition point 101 in the fingerprint acquisition array, a ROW of acquisition points 102 made up of a number of acquisition points, a COLUMN of acquisition points 103 made up of a number of acquisition points, a acquisition array 104 made up of a number of COLUMNs of acquisition points, a finger excitation signal 105, a finger equivalent capacitance 106, a proportional amplification capacitance 107, an acquisition point internal amplification circuit 108, a reset switch 109, an acquisition point output drive tube 110, a ROW selection control tube 111 (row_sel), a COLUMN selection control tube 113 (column_sel), a discharge node 115 (i.e., an output common node of the fingerprint sensor acquisition array), an active load circuit 116, a parasitic capacitance 118 on the discharge node 115, a fingerprint sensor acquisition array back driver 119, an output 120 of the fingerprint sensor acquisition array, an acquisition point power supply 112, and further, a fingerprint sensor ground terminals 117 and 121. The size of the parasitic capacitance 118 is determined by the number of collection points in the fingerprint sensor collection array, the larger the number, the more devices and traces on the discharge node 115, and the larger the capacitance value of the parasitic capacitance 118. The row selection control pipe 111 outputs a row selection control signal 112, and the column selection control pipe 113 outputs a column selection control signal 114.
The operation of the conventional fingerprint sensor 100 is described as follows, and when the row selection control signal 112 and the column selection control signal 114 are simultaneously high, the row selection control tube 111 and the column selection control tube 113 are simultaneously turned on as switches, indicating that the current acquisition point is selected. After the collection point is selected, the reset switch 109 is turned on first, the whole circuit in the selected collection point enters a reset state, and the collection point output driving tube 110 is used as a follower under the normal bias condition of the active load circuit 116, so that the state of the discharge node 115 follows the reset voltage in the collection point. The discharging node 115 follows the process of voltage establishment, which is the process in which the active load circuit 116 discharges the charge residing on the parasitic capacitance 118 at the previous time, and the speed at which the discharging node 115 follows the voltage establishment depends on the magnitude of the parasitic capacitance 118 and the magnitude of the current of the active load circuit 116. After the reset state is finished, the reset switch 109 is turned off, the collection point enters a fingerprint collection state, the loaded finger excitation signal 105 is amplified (or reduced) in proportion through the finger equivalent capacitor 106 and the proportional amplifying capacitor 107, the fingerprint small signal is transmitted to the outside of the fingerprint collection array through the output driving tube 110, and is driven by the fingerprint sensor collection array rear driver 119 to be output.
When the reset switch 109 is turned on, the acquisition point circuit is in a reset state, and a normal static working point is established inside the circuit. When the reset switch 109 is turned off, the acquisition point circuit enters a fingerprint acquisition state, and the capacitance between the acquisition point and the finger fingerprint is converted into a voltage. The circuit operates near the last quiescent operating point. After the acquisition point is selected by the address signal (i.e., when the row selection control tube 111 and the column selection control tube 113 are turned on simultaneously as switches), the acquisition point is in a reset state and fingerprint acquisition is performed.
Specifically, the fingerprint acquisition process mainly comprises: 1. the selected acquisition point, namely the acquisition point selected by the simultaneous conduction of the row selection control tube 111 and the column selection control tube 113, is called an effective acquisition point; 2. resetting the acquisition point circuit, wherein the acquisition point circuit is in a reset state, the acquisition point circuit establishes a normal static working point, and simultaneously clears the charge on the proportional amplifying capacitor 107; 3. the fingerprint collection, the collection point circuit enters a fingerprint collection state, and the collection point circuit realizes the conversion from capacitance to voltage near the static working point. The output voltage vo=vi×cf/Ca, where Vi is the amplitude of the finger excitation signal 105, cf is the finger equivalent capacitance 106, and Ca is the proportional amplifying capacitance 107.
The inventor further analyzed that the conventional active load circuit, as shown in fig. 2, the active load circuit 116 is generally formed by a common current source, and includes a power supply 201, a current source PMOS transistor 202 and a current mirror 200, the current mirror 200 includes a current mirror input NMOS transistor 204 and a current mirror output NMOS transistor 205, the source of the current source PMOS transistor 202 is connected to the power supply 201, the gate of the current source PMOS transistor 202 is connected to a bias voltage 203 (VBP), the drain of the current source PMOS transistor 202 is connected to the drain of the current mirror input NMOS transistor 204, the gate of the current mirror input NMOS transistor 204 is connected to the gate of the current mirror output NMOS transistor 205, and the drain of the current mirror output NMOS transistor 205 is connected to the discharge node 115 of the fingerprint sensor acquisition array, so as to provide the necessary bias current to the acquisition point output drive transistor 110, and the ratio of the bias current to the current mirror input NMOS transistor 204 is equal to the ratio of the sizes of the current mirror output NMOS transistor 205 and the current mirror input NMOS transistor 204; the sources of the current mirror input NMOS tube 204 and the current mirror output NMOS tube 205 are grounded. The bias voltage 203 (VBP) and the current source PMOS transistor 202 together determine the current level of the active load circuit 116, and the current of the current mirror input NMOS transistor 204 is equal to the current level of the current source PMOS transistor 202.
The inventor analyzes and finds that when the selected acquisition point is in a reset state, the conventional current source discharges the discharge node 115, and as the current source only can provide constant current bias, the charge discharge speed on the discharge node 115 is limited, so that the reset time of each acquisition point is greatly prolonged, and the acquisition speed of the acquisition array is reduced. Therefore, to increase the acquisition speed of the fingerprint image, it is necessary to start with increasing the discharge speed of the electric charges on the discharge node 115.
The inventor considers improving the conventional active load circuit, and adds an auxiliary discharging path on the basis of a current source so as to improve the discharging speed of charges on a common node and shorten the reset time of each acquisition point. As shown in fig. 3, the improved active load circuit 11600 includes a current source and an auxiliary discharging path 3000, the auxiliary discharging path 3000 is connected in parallel with the current source, one end of the auxiliary discharging path 3000 is connected to the discharging node 115 of the fingerprint sensor acquisition array, the other end is grounded, and the auxiliary discharging path 3000 rapidly discharges the discharging node 115 in the fingerprint sensor acquisition array reset state.
One of the common structures of the current source comprises a power supply 201, a current source PMOS tube 202 and a current mirror 200, the current mirror 200 comprises a current mirror input NMOS tube 204 and a current mirror output NMOS tube 205, the source electrode of the current source PMOS tube 202 is connected with the power supply 201, the grid electrode of the current source PMOS tube 202 is connected with a bias voltage 203 (VBP), the drain electrode of the current source PMOS tube 202 is connected with the drain electrode of the current mirror input NMOS tube 204, the grid electrode of the current mirror input NMOS tube 204 is connected with the grid electrode of the current mirror output NMOS tube 205, the drain electrode of the current mirror output NMOS tube 205 is connected with the discharge node 115 of the fingerprint sensor acquisition array, and the source electrodes of the current mirror input NMOS tube 204 and the current mirror output NMOS tube 205 are grounded.
Further, the inventor has conducted intensive studies and developed an auxiliary discharge path, and one structure of the auxiliary discharge path shown in fig. 4 is a strong discharge path, and the improved active load circuit 11601 includes a strong discharge NMOS 300, a gate access control signal 301 of the strong discharge NMOS, a source of the strong discharge NMOS is grounded, and a drain of the strong discharge NMOS is connected to the discharge node 115. In the fingerprint sensor acquisition array reset state, enabling the strong discharge path, namely, changing a control signal of the grid electrode of the strong discharge NMOS tube 300 into a high level, controlling the conduction of the strong discharge NMOS tube 300, enabling the strong discharge NMOS tube 300 to be in a triode region, enabling the strong discharge NMOS tube 300 to be equivalent to a small resistor at the moment, and rapidly discharging the charge of the discharge node 115 to the ground through the strong discharge NMOS tube 300; before entering the fingerprint collection state (the second half period of the reset state), the strong discharge path is closed, that is, the control signal of the grid electrode of the strong discharge NMOS tube 300 becomes low level, under the normal bias of the current mirror output NMOS tube 205, the output driving tube 110 of the selected collection point of the fingerprint sensor collection array drives the parasitic capacitor 118 to quickly return to the normal bias state, so as to prepare for the fingerprint collection state of the next stage.
When this strong discharge path is enabled, a large transient current is generated, which can inject noise into the power and ground of the fingerprint sensor. However, the large transient current does not affect the normal use of the fingerprint acquisition sensor, but is a theoretical disadvantage.
As another improved structure of the auxiliary discharging path shown in fig. 5, the improved active load circuit 11602 includes a dummy pick-up point (dummy pixel) 406, a dummy pick-up point output stage current source NMOS transistor 407, an operational amplifier 403, and an auxiliary conducting NMOS transistor 400, the drains of the dummy pick-up point (dummy pixel) 406 and the dummy pick-up point output stage current source NMOS transistor 407 are connected and generate a reference Voltage (VREF) 402, the reference Voltage (VREF) 402 is used as an inverting input of the operational amplifier 403, a forward input of the operational amplifier 403 is connected to a discharging node, an output of the operational amplifier 403 is connected to a gate of the auxiliary conducting NMOS transistor 400, a drain of the auxiliary conducting NMOS transistor 400 is connected to the discharging node, a gate of the dummy pick-up point output stage current source NMOS transistor 407 is connected to a gate of the current mirror output NMOS transistor 205, and a source of the dummy pick-up point output stage current source NMOS transistor 407 and a source of the auxiliary conducting NMOS transistor 400 are grounded.
The auxiliary conduction NMOS 400 may be an N-type metal oxide semiconductor, and the output of the operational amplifier 403 controls the conduction state of the auxiliary conduction NMOS 400, specifically, the operational amplifier 403 calculates the difference between the voltage of the discharge node 115 and the reference Voltage (VREF) 402, and when the difference is greater than 0, the output voltage of the operational amplifier 403 increases the conduction capability of the auxiliary conduction NMOS 400, and enhances the discharge capability of the discharge node 115; in response to the difference becoming smaller, the output voltage of the operational amplifier 403 decreases the turn-on capability of the auxiliary turn-on NMOS 400, decreasing the discharge capability to the discharge node 115, and when the difference is equal to 0, the individual acquisition point 101 in the fingerprint acquisition array enters a normal bias state.
The inventor further optimizes the auxiliary discharging path in fig. 5 to obtain another improved structure of the auxiliary discharging path shown in fig. 6, and the improved active load circuit 11603 combines the current mirror output NMOS 205 and the auxiliary conduction NMOS 400 into a power supply/conduction NMOS 501, and adopts the accelerating discharging switch 502 and the normal bias switch 503 to perform time-sharing switching control.
Specifically, the improved active load circuit 11603 includes a dummy pixel 406, a dummy output stage current source NMOS 407, an operational amplifier 403, an accelerated discharge switch 502, a normal bias switch 503, and a power/on NMOS 500, the dummy pixel 406 and the drain of the dummy output stage current source NMOS 407 are connected and generate a reference Voltage (VREF) 402, the reference Voltage (VREF) 402 is used as the inverting input of the operational amplifier 403, the forward input of the operational amplifier 403 is connected to the discharge node 115, the output of the operational amplifier 403 is connected to the gate of the power/on NMOS 500, the drain of the power/on NMOS 500 is connected to the discharge node, the gate of the dummy output stage current source NMOS 407 is connected to the gate of the power/on NMOS 500, the source of the dummy output stage current source NMOS 407 and the source of the power/on NMOS 500 are grounded, the accelerated discharge switch 502 is disposed between the output of the operational amplifier 403 and the gate of the power/on NMOS 500, and the normal bias switch 503 is disposed between the gate of the dummy output stage NMOS 407 and the gate of the power/on NMOS 500.
The time-sharing switching control of the accelerated discharging switch 502 and the normal biasing switch 503 means that when the collection point selected by the fingerprint sensor collection array enters a reset state, the accelerated discharging switch 502 is closed, the normal biasing switch 503 is opened, the operational amplifier 403 and the power/conduction NMOS tube 500 form a negative feedback loop, the power/conduction NMOS tube 500 serves as an auxiliary conduction NMOS tube, the discharging node 115 is rapidly discharged, and the voltage of the discharging node 115 is rapidly recovered to the reference Voltage (VREF) 402; when the collection point selected by the fingerprint sensor collection array enters a fingerprint collection state, the accelerated discharge switch 502 is opened, the normal bias switch 503 is closed, and the power/conduction NMOS tube 500 serves as a current mirror output NMOS tube to provide constant current bias for the single collection point 101 in the fingerprint collection array.
For the virtual collection point (dummy pixel) 406 in fig. 5 and 6, a preferred structure includes a virtual collection point proportional amplifying capacitor 607, a virtual collection point internal amplifying circuit 608, a virtual collection point row selection control pipe 611, a virtual collection point column selection control pipe 613, a virtual collection point output driving pipe 610 and a virtual collection point power supply 622, the virtual collection point proportional amplifying capacitor 607 and the virtual collection point internal amplifying circuit 608 are connected in parallel, two ends of the virtual collection point proportional amplifying capacitor 607 are shorted, the virtual collection point internal amplifying circuit 608 is connected with a gate of the virtual collection point output driving pipe 610, a drain of the virtual collection point output driving pipe 610 is connected with the virtual collection point power supply 622, a source of the virtual collection point output driving pipe 610 is connected with a drain of the virtual collection point row selection control pipe 611, a source of the virtual collection point row selection control pipe 611 is connected with a drain of the virtual collection point column selection control pipe 613, a source of the virtual collection point column selection control pipe 607 is connected with the drain of the virtual collection point output stage NMOS pipe 407, and the virtual collection point selection pipe 613 is in a state of being connected with the virtual collection point selection pipe 613.
The inventor designs a fingerprint sensor 10000, and uses the active load circuit based on the output stage of the fingerprint sensor acquisition array in any of the above embodiments, as shown in fig. 7, the active load circuit adopts a modified active load circuit 11601, and may also be replaced by 11602 or 11603.
The inventors devised a circuit using the fingerprint sensor in the above embodiment. As shown in fig. 8, the fingerprint sensor is connected to a micro control unit (Microcontroller Unit, MCU) or the like, so as to realize a fingerprint recognition function. The MCU can be replaced by a single chip microcomputer unit or a chip with calculation and processing functions.
The foregoing describes in detail preferred embodiments of the present invention. It should be understood that numerous modifications and variations can be made in accordance with the concepts of the invention by one of ordinary skill in the art without undue burden. Therefore, all technical solutions which can be obtained by logic analysis, reasoning or limited experiments based on the prior art by the person skilled in the art according to the inventive concept shall be within the scope of protection defined by the claims.
Claims (8)
1. The active load circuit based on the fingerprint sensor acquisition array output stage is characterized by comprising a current source and an auxiliary discharge path, wherein the auxiliary discharge path is connected with the current source in parallel, one end of the auxiliary discharge path is connected with a discharge node of the fingerprint sensor acquisition array, the other end of the auxiliary discharge path is grounded, and the auxiliary discharge path rapidly discharges the discharge node in a reset state of the fingerprint sensor acquisition array; the current source comprises a power supply, a current source PMOS tube and a current mirror, the current mirror comprises a current mirror input NMOS tube and a current mirror output NMOS tube, the source electrode of the current source PMOS tube is connected with the power supply, the grid electrode of the current source PMOS tube is connected with bias voltage VBP, the drain electrode of the current source PMOS tube is connected with the drain electrode of the current mirror input NMOS tube, the grid electrode of the current mirror input NMOS tube is connected with the grid electrode of the current mirror output NMOS tube, the drain electrode of the current mirror output NMOS tube is connected with the discharge node, and the source electrodes of the current mirror input NMOS tube and the current mirror output NMOS tube are grounded; the auxiliary discharging path comprises a strong discharging NMOS tube, a grid electrode of the strong discharging NMOS tube is connected with a control signal, a source electrode of the strong discharging NMOS tube is grounded, a drain electrode of the strong discharging NMOS tube is connected with the discharging node, the control signal of the grid electrode of the strong discharging NMOS tube is changed into a high level under the condition that the fingerprint sensor is in an acquisition array reset state, the strong discharging NMOS tube is controlled to be conducted, the strong discharging NMOS tube is in a triode region, the strong discharging NMOS tube is equivalent to a small resistor, and the charge of the discharging node is quickly discharged to the ground through the strong discharging NMOS tube; before entering a fingerprint acquisition state, a strong discharge passage is closed, a control signal of a grid electrode of the strong discharge NMOS tube becomes low level, and under the normal bias of the output NMOS tube of the current mirror, an output driving tube in the selected acquisition point of the fingerprint sensor acquisition array drives parasitic capacitance to quickly return to the normal bias state, so that preparation is made for the fingerprint acquisition state of the next stage.
2. The active load circuit based on the fingerprint sensor acquisition array output stage is characterized by comprising a current source and an auxiliary discharge path, wherein the auxiliary discharge path is connected with the current source in parallel, one end of the auxiliary discharge path is connected with a discharge node of the fingerprint sensor acquisition array, the other end of the auxiliary discharge path is grounded, and the auxiliary discharge path rapidly discharges the discharge node in a reset state of the fingerprint sensor acquisition array; the current source comprises a power supply, a current source PMOS tube and a current mirror, the current mirror comprises a current mirror input NMOS tube and a current mirror output NMOS tube, the source electrode of the current source PMOS tube is connected with the power supply, the grid electrode of the current source PMOS tube is connected with bias voltage VBP, the drain electrode of the current source PMOS tube is connected with the drain electrode of the current mirror input NMOS tube, the grid electrode of the current mirror input NMOS tube is connected with the grid electrode of the current mirror output NMOS tube, the drain electrode of the current mirror output NMOS tube is connected with the discharge node, and the source electrodes of the current mirror input NMOS tube and the current mirror output NMOS tube are grounded; the auxiliary discharging path comprises a virtual acquisition point (dummy pixel), a virtual acquisition point output stage current source NMOS tube, an operational amplifier and an auxiliary conduction NMOS tube, wherein the virtual acquisition point (dummy pixel) is connected with the drain electrode of the virtual acquisition point output stage current source NMOS tube and generates a reference voltage VREF, the reference voltage VREF is used as the reverse input of the operational amplifier, the forward input of the operational amplifier is connected with the discharging node, the output of the operational amplifier is connected with the grid electrode of the auxiliary conduction NMOS tube, the drain electrode of the auxiliary conduction NMOS tube is connected with the discharging node, the grid electrode of the virtual acquisition point output stage current source NMOS tube is connected with the grid electrode of the current mirror output NMOS tube, and the source electrode of the virtual acquisition point output stage current source NMOS tube is grounded with the source electrode of the auxiliary conduction NMOS tube; the auxiliary conduction NMOS tube is an N-type metal oxide semiconductor tube, the output of the operational amplifier controls the conduction state of the auxiliary conduction NMOS tube, the operational amplifier calculates the difference value between the voltage of the discharge node and the reference voltage VREF, when the difference value is larger than 0, the output voltage of the operational amplifier increases the conduction capacity of the auxiliary conduction NMOS tube, the discharge capacity of the discharge node is enhanced, the output voltage of the operational amplifier decreases the conduction capacity of the auxiliary conduction NMOS tube in response to the gradual decrease of the difference value, the discharge capacity of the discharge node is weakened, and when the difference value is equal to 0, the acquisition point output driving tube selected by the fingerprint sensor acquisition array enters a normal bias state.
3. The active load circuit based on the fingerprint sensor acquisition array output stage is characterized by comprising a current source and an auxiliary discharge path, wherein the auxiliary discharge path is connected with the current source in parallel, one end of the auxiliary discharge path is connected with a discharge node of the fingerprint sensor acquisition array, the other end of the auxiliary discharge path is grounded, and the auxiliary discharge path rapidly discharges the discharge node in a reset state of the fingerprint sensor acquisition array; the current source comprises a power supply, a current source PMOS tube and a current mirror, the current mirror comprises a current mirror input NMOS tube and a current mirror output NMOS tube, the source electrode of the current source PMOS tube is connected with the power supply, the grid electrode of the current source PMOS tube is connected with bias voltage VBP, the drain electrode of the current source PMOS tube is connected with the drain electrode of the current mirror input NMOS tube, the grid electrode of the current mirror input NMOS tube is connected with the grid electrode of the current mirror output NMOS tube, the drain electrode of the current mirror output NMOS tube is connected with the discharge node, and the source electrodes of the current mirror input NMOS tube and the current mirror output NMOS tube are grounded; the auxiliary conduction NMOS tube and the current mirror output NMOS tube are combined into a power supply/conduction NMOS tube, an accelerated discharge switch is arranged between the output of the operational amplifier and the grid electrode of the power supply/conduction NMOS tube, the drain electrode of the power supply/conduction NMOS tube is connected with the discharge node, the grid electrode of the virtual acquisition point output stage current source NMOS tube is connected with the grid electrode of the power supply/conduction NMOS tube, a normal bias switch is arranged between the grid electrode of the virtual acquisition point output stage current source NMOS tube and the grid electrode of the power supply/conduction NMOS tube, and the source electrode of the virtual acquisition point output stage current source NMOS tube is grounded.
4. The active load circuit based on the fingerprint sensor acquisition array output stage of claim 3, wherein the accelerated discharge switch and the normal bias switch perform time-sharing switching control on the power/on NMOS tube, when the acquisition point selected by the fingerprint sensor acquisition array enters a reset state, the accelerated discharge switch is closed, the normal bias switch is opened, the power/on NMOS tube serves as an auxiliary on NMOS tube to rapidly discharge the discharge node, so that the voltage of the discharge node is rapidly recovered to a reference voltage VREF, when the acquisition point selected by the fingerprint sensor acquisition array enters a fingerprint acquisition state, the accelerated discharge switch is opened, the normal bias switch is closed, and the power/on NMOS tube serves as a current mirror output NMOS tube to provide constant current bias for the acquisition point selected by the fingerprint sensor acquisition array.
5. The fingerprint sensor acquisition array output stage-based active load circuit as claimed in any one of claims 1 to 4, wherein the virtual acquisition point (dummy pixel) includes a virtual acquisition point proportional amplification capacitor, a virtual acquisition point internal amplification circuit, a virtual acquisition point row selection control pipe, a virtual acquisition point column selection control pipe, a virtual acquisition point output driving pipe, and a virtual acquisition point power supply, the virtual acquisition point proportional amplification capacitor and the virtual acquisition point internal amplification circuit are connected in parallel, two ends of the virtual acquisition point proportional amplification capacitor are shorted, the virtual acquisition point internal amplification circuit is connected with a gate of the virtual acquisition point output driving pipe, a drain of the virtual acquisition point output driving pipe is connected with the virtual acquisition point power supply, a source of the virtual acquisition point output driving pipe is connected with a drain of the virtual acquisition point row selection control pipe, a source of the virtual acquisition point row selection control pipe is connected with a drain of the virtual acquisition point column selection control pipe, a source of the virtual acquisition point column selection control pipe is connected with the virtual acquisition point output driving pipe, and the virtual acquisition point column selection control pipe is connected with the drain of the virtual acquisition point selection control pipe.
6. The active load circuit of any one of claims 1 to 4, wherein when a selected acquisition point of the fingerprint sensor acquisition array enters a reset state, the operational amplifier calculates a difference between the voltage of the discharge node and the reference voltage VREF, and when the difference is greater than 0, the output voltage of the operational amplifier increases the conduction capability of the auxiliary conduction NMOS, enhances the discharge capability of the discharge node, and in response to the difference becoming smaller, the output voltage of the operational amplifier decreases the conduction capability of the auxiliary conduction NMOS, weakens the discharge capability of the discharge node, and when the difference is equal to 0, the selected acquisition point of the fingerprint sensor acquisition array outputs a driving tube into a normal bias state.
7. A fingerprint sensor comprising an active load circuit according to any one of claims 1-6 based on a fingerprint sensor acquisition array output stage.
8. A circuit is characterized in that, comprising a fingerprint sensor as claimed in claim 7.
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| CN105391958A (en) * | 2015-11-05 | 2016-03-09 | 南京邮电大学 | Low-power-consumption column-readout-stage circuit in infrared readout integrated circuit |
| US9736413B1 (en) * | 2016-02-03 | 2017-08-15 | Sony Corporation | Image sensor and electronic device with active reset circuit, and method of operating the same |
| CN106056052B (en) * | 2016-03-25 | 2019-09-17 | 深圳市奔凯安全技术股份有限公司 | A kind of fingerprint collecting circuit |
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