The present invention relates to a fingerprint sensing module, and more particularly to a fingerprint sensing module capable of eliminating a memory effect.
With the maturity of the modern fingerprint sensing technology, fingerprint sensing modules have been widely used in various electronic devices. For example, under-display fingerprint sensing modules have been applied to smart mobile devices such as digital cameras, scanners, smart phones, tablet computers or notebook computers.
When the pixel row P1 receives a control signal C1, the plurality of sensing pixels P11˜P1n are sequentially driven to output the sensed contents. In the time interval between 0 and t11, the sensed content of the sensing pixel P11 is outputted to the row output node N1 according to the control signal C11. Consequently, the output voltage V1out with a first voltage level V11 is outputted from the row output node N1. In the time interval between t11 and t12, the sensed content of the sensing pixel P12 is outputted to the row output node N1 according to the control signal C12. Consequently, the output voltage V1out with a second voltage level V12 is outputted from the row output node N1. In the time interval between t12 and t13, the sensed content of the sensing pixel P13 is outputted to the row output node N1 according to the control signal C13. Consequently, the output voltage V1out with a third voltage level V13 is outputted from the row output node N1.
Due to the parasitic effect of the practical circuitry wiring structure, a memory effect is generated when the output voltage V1out from the sensing pixels P11˜P1n is sequentially read at different time points. For example, when one of the sensing pixels P11˜P1n is driven and the corresponding sensed content is read, the output voltage V1out corresponding to the previous sensing pixel is still retained at the row output node N1. Because of the memory effect, the sensed contents of the sensing pixels P11˜P1n to be outputted to the row output node N1 are adversely affected.
As mentioned above, the results of reading the sensed data of the fingerprint sensing pixel array 110 are adversely affected by the memory effect. For solving this drawback, a fingerprint sensing module as shown in
When the pixel row P2 receives a control signal C2, the plurality of sensing pixels P21˜P2n are sequentially driven to output the sensed contents. In the time interval between 0 and t21, the sensed content of the sensing pixel P21 is outputted to the row output node N2 according to the control signal C21. Consequently, the output voltage V2out with a first voltage level V21 is outputted from the row output node N2. Then, the control switch 230 is turned on in response to a reset signal Rst2. Consequently, the voltage level V21 of the output voltage V2out is equal to the voltage level of the first voltage VN21 and the voltage level of the second voltage VN22. That is, the voltage level V21 of the output voltage V2out is pulled down to 0V. Consequently, the residual memory effect caused by the sensing pixel P21 is eliminated.
In the time interval between t21 and t22, the sensed content of the sensing pixel P22 is outputted to the row output node N2 according to the control signal C22. Consequently, the output voltage V2out with a second voltage level V22 is outputted from the row output node N2. Then, the control switch 230 is turned on again in response to the reset signal Rst2. Consequently, the voltage level V22 of the output voltage V2out is pulled down to 0V. Consequently, the residual memory effect caused by the sensing pixel P22 is eliminated. The rest may be deduced by analog, and the voltage levels of the output voltage V2out from the pixel row P2 can be acquired.
As mentioned above, the voltage level of the first voltage VN21 is assumed to be equal to the voltage level of the second voltage VN22. When the control switch 230 is turned on to eliminate the memory effect, the voltage levels at the two terminals of the current source 220 are pulled to the same voltage level. Since there is no voltage difference between the two terminals of the current source 220, the driving capability of the current source 220 is lost and the current source 220 is disabled.
During the switching periods t21 to t2n, the terminal of the current source 220 electrically coupled to the row output node N2 has to slowly pull up the voltage level of the row output node N2 through the pixel row P2. Since the voltage level of the row output node N2 is increased, a voltage difference exists between the two terminals of the current source 220. Consequently, the current source 220 is enabled again until the voltage level at the row output node N2 is high enough to result in the normal operation of the current source 220. That is, it is necessary to increase the voltage level of the row output node N2 in advance in order to get better output of the current source 220. Consequently, the time interval between t21 and t2n contains the time period of increasing the voltage level of the row output node N2 to the operating voltage level of the current source 230 and the waiting time period of pulling down the voltage level of the output voltage V2out to 0V. In other words, the signal switching speed cannot be too fast. In practice, the voltage level of the row output node N2 ranges from 0V to the voltage level of the output voltage V2out. Consequently, it is necessary to pull down the voltage level of the row output node N2 to 0V to eliminate the residual memory effect of the sensing pixels P21˜P2n. Moreover, after the voltage level reaches the operating voltage level of the current source 220, the sensed contents of the sensing pixels can be normally read. Consequently, the switching time intervals t21-t2n of reading the sensed contents of the sensing pixels P21˜P2n are very long.
Therefore, there is a need of providing a novel fingerprint sensing module for effectively shortening the switching time period of reading pixels and eliminating the memory effect of the previous sensing pixel so as to overcome the drawbacks of the conventional technologies.
For overcoming the drawbacks of the conventional technologies, the present invention provides a fingerprint sensing module with a control switch. When the control switch is turned on in response to a reset signal, the voltage level of an output voltage from a row output node (or a column output node) is equal to or close to a voltage level of a second voltage.
In accordance with an aspect of the present invention, a fingerprint sensing module is provided. The fingerprint sensing module includes a fingerprint sensing pixel array, a current source and a plurality of control switches. The fingerprint sensing pixel array includes a plurality of sensing pixels, which are arranged in a plurality of columns and a plurality of rows. The sensing pixels of each column are electrically coupled to a column output node, so that a plurality of column output nodes are electrically coupled to the plurality of sensing pixels of the fingerprint sensing pixel array. In response to a control signal, sensed contents of the sensing pixels in each column are outputted to the column output node. A first terminal of the current source is electrically coupled to the plurality of column output nodes. A second terminal of the current source is electrically coupled to a first voltage. A first terminal of each control switch is electrically coupled to the plurality of column output nodes. A second terminal of each control switch is electrically coupled to a second voltage. A voltage level of the second voltage is different from a voltage level of the first voltage. After the sensed contents of the plurality of sensing pixels are outputted and the plurality of control switches are turned on in response to a reset signal, a voltage level of an output voltage at the column output node corresponding to the sensing pixels of each column is equal to or close to the voltage level of the second voltage.
In accordance with another aspect of the present invention, a fingerprint sensing module is provided. The fingerprint sensing module includes a fingerprint sensing pixel array, a current source and a plurality of control switches. The fingerprint sensing pixel array includes a plurality of sensing pixels, which are arranged in a plurality of rows and a plurality of rows. The sensing pixels of each row are electrically coupled to a row output node, so that a plurality of row output nodes are electrically coupled to the plurality of sensing pixels of the fingerprint sensing pixel array. In response to a control signal, sensed contents of the sensing pixels in each row are outputted to the row output node. A first terminal of the current source is electrically coupled to the plurality of row output nodes. A second terminal of the current source is electrically coupled to a first voltage. A first terminal of each control switch is electrically coupled to the plurality of row output nodes. A second terminal of each control switch is electrically coupled to a second voltage. A voltage level of the second voltage is different from a voltage level of the first voltage. After the sensed contents of the plurality of sensing pixels are outputted and the plurality of control switches are turned on in response to a reset signal, a voltage level of an output voltage at the row output node corresponding to the sensing pixels of each row is equal to or close to the voltage level of the second voltage.
From the above descriptions, the fingerprint sensing module of the present invention is additionally equipped with a control switch. After the control switch is turned on in response to the reset signal, the voltage level of the output voltage from the fingerprint sensing pixel array is pulled down to the voltage level of the second voltage. Consequently, the memory effect of each sensing pixel can be eliminated. Moreover, the voltage level of two terminals of the current source is within the range from the voltage level of the first voltage to the voltage level of the second voltage. Due to the difference between the voltage levels of the first voltage and the second voltage, the current source is in a standby state. When the current source in a standby state, the current source can enter the normal working state at any time. Consequently, the switching time period of reading the sensed content of each sensing pixel of the fingerprint sensing pixel array is shortened.
The above objects and advantages of the present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, in which:
The embodiments of present invention will be described more specifically with reference to the following drawings. In the following embodiments and drawings, the elements irrelevant to the concepts of the present invention or the elements well known to those skilled in the art are omitted. It is noted that numerous modifications and alterations may be made while retaining the teachings of the invention.
For overcoming the drawbacks of the conventional technologies, the present invention provides a novel fingerprint sensing module.
As shown in
In an embodiment, the voltage level of the first voltage VN31 and the voltage level of the second voltage VN32 are different. For example, the voltage level of the second voltage VN32 is higher than the voltage level of the first voltage VN31. The second voltage VN32 is provided by a voltage generation circuit. For example, the voltage generation circuit is another current source, a biasing circuit or a buffer. In this embodiment, the voltage level of the second voltage VN32 is equal to VD. For example, the voltage level of VD is 3V or 3.3V.
When the pixel row P3 receives a control signal C3, the plurality of sensing pixels P31˜P3 are sequentially driven to output the sensed contents. In the time interval between 0 and t31, the sensed content of the sensing pixel P31 is outputted to the row output node N3 according to the control signal C31. Consequently, the output voltage V3out with a first voltage level V31 is outputted from the row output node N3. Then, the control switch 330 is turned on in response to a reset signal Rst3. Consequently, the first voltage level V31 of the output voltage V3out from the row output node N3 is equal to the voltage level of the second voltage VN32. That is, the first voltage level V31 of the output voltage V3out is pulled down to VD. Since there is no voltage difference between the first voltage level V31 of the output voltage V3out and the voltage level of the second voltage VN32, the residual memory effect caused by the sensing pixel P31 is eliminated.
In the time interval between t31 and t32, the sensed content of the sensing pixel P32 is outputted to the row output node N3 according to the control signal C32. Consequently, the output voltage V3out with a second voltage level V32 is outputted from the row output node N3. Then, the control switch 330 is turned on in response to the reset signal Rst3. Consequently, the second voltage level V32 of the output voltage V3out from the row output node N3 is pulled down to VD, and the residual memory effect caused by the sensing pixel P32 is eliminated.
In the time interval between t32 and t33, the sensed content of the sensing pixel P33 is outputted to the row output node N3 according to the control signal C33. Consequently, the output voltage V3out with a third output voltage level V33 is outputted from the row output node N3. Then, the control switch 330 is turned on in response to the reset signal Rst3. Consequently, the third voltage level VN33 of the output voltage V3out from the row output node N3 is pulled down to VD, and the residual memory effect caused by the sensing pixel P33 is eliminated.
The rest may be deduced by analog. In such way, the voltage levels of the output voltage V3out from the pixel row P3 can be acquired sequentially.
From the above descriptions, the process of reading the pixel row P3 according to the present invention is beneficial. After the sensed content of the sensing pixel P31 is read and the output voltage V3out with the first voltage level V31 is outputted to the row output node N3, the first output voltage level V31 is pulled down to VD. Consequently, in the subsequent step, the sensed content of the sensing pixel P32 can be quickly read and the output voltage V3out with the second voltage level V32 can be outputted to the row output node N3. In other words, the long waiting time period of pulling down the voltage level of the output voltage V3out to the voltage level of the first voltage VN31 (e.g., a ground voltage level) is not required. Moreover, it is not necessary to increase the voltage level of the output voltage level V3out again to enable the current source 320. When the desired voltage difference between the two terminals of the current source 320 is achieved, the subsequent steps of reading the sensing contents of the sensing pixels of the pixel row P3 can be performed. In such way, the time interval between t31 and t3n for decreasing the difference between the voltage level of the output voltage level V3out and the voltage level of the second voltage VN32 is shortened. Consequently, the switching time intervals t31˜t31, of the sensing pixels P31˜P31, in the pixel row P3 are obviously shorter than the switch time intervals t21-t2n of the sensing pixels P21˜P2n in the conventional fingernail sensing module.
Moreover, when the control switch 330 is turned on, the voltage levels at the two terminals of the current source 320 are within the range from the voltage level of the first voltage VN31 to the voltage level of the second voltage VN32. Since the current source 320 has the voltage difference between the voltage level of the first voltage VN31 and the voltage level of the second voltage VN32, the current source 320 is in a standby state. When the current source 320 is in a standby state, the current source 320 can enter the normal working state at any time. That is, the current source 320 can be enabled again without the need of receiving the voltage level from the row output node N3.
It is noted that numerous modifications and alterations may be made while retaining the teachings of the invention. That is, the structural designs and specifications of the components may be varied according to the practical requirements. For example, the control switch is a transistor. According to the initial voltage value of the fingerprint sensing pixel array, the voltage level of the second voltage is dynamically adjusted to the proper voltage level VD. For example, the voltage level of the second voltage is specially set. Consequently, the voltage level of the terminal receiving the reset signal Rst minus the voltage level VD of the second voltage is certainty higher than the gate startup voltage Vth.
As mentioned above, the fingerprint sensing pixel array includes a plurality sensing pixels, which are arranged in a plurality of columns and a plurality of rows. In an embodiment, the output terminals of the plurality of sensing pixels in any column are electrically coupled to a column output node. Alternatively, in another embodiment, the output terminals of the plurality of sensing pixels in any row are electrically coupled to a row output node.
In the above embodiment, the current source and the control switch are electrically coupled to any row output signal. In accordance with the spirits of the present invention, the first terminal of the current source and the first terminal of the control switch are electrically coupled to the first voltage and the second voltage, respectively. After the control switch is turned on in response to the reset signal, the voltage level of the output voltage of the fingerprint sensing pixel array is pulled down to the voltage level of the second voltage. Consequently, the memory effect of each sensing pixel can be eliminated. Alternatively, the current source and the control switch are electrically coupled to any column output signal. Similarly, the purpose of eliminating the memory effect can be achieved.
From the above descriptions, the fingerprint sensing module of the present invention is additionally equipped with a control switch. After the control switch is turned on in response to the reset signal, the voltage level of the output voltage from the fingerprint sensing pixel array is pulled down to the voltage level of the second voltage. Consequently, the memory effect of each sensing pixel can be eliminated. Moreover, the voltage level of the two terminals of the current source is within the range from the voltage level of the first voltage to the voltage level of the second voltage. Due to the difference between the voltage levels of the first voltage and the second voltage, the current source is in a standby state. When the current source in a standby state, the current source can enter the normal working state at any time. Consequently, the switching time period of reading the sensed content of each sensing pixel of the fingerprint sensing pixel array is shortened.
While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all modifications and similar structures.
Number | Date | Country | Kind |
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201910556231.3 | Jun 2019 | CN | national |
This application claims priority to U.S. Provisional Patent Application No. 62/740,367 filed Oct. 2, 2018 and Chinese Patent Application No. 201910556231.3 file Jun. 25, 2019, the contents of which are incorporated herein by reference.
Number | Date | Country | |
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62740367 | Oct 2018 | US |