Image sensing system and circuit

Abstract

The present invention discloses an image sensing system and circuit. The image sensing system includes a panel and an image sensing circuit. The panel includes a plurality of sensing pixels, a plurality of sensing lines and at least one first current source, wherein each sensing line is coupled to a column of sensing pixels among the plurality of sensing pixels, and each first current source is coupled to one of the plurality of sensing lines. The image sensing circuit is coupled to the panel, and includes at least one second current source, wherein each second current source is coupled to one of the plurality of sensing lines. A first sensing line among the plurality of sensing lines is coupled to a first current source among the at least one first current source, and is coupled to a second current source among the at least one second current source.

Description

Technical Field

[0001] The present invention relates to an image sensing system and circuit, and in particular to a fingerprint image sensing system and circuit. Background Art

[0002] Fingerprint sensing technology has been widely used in a variety of electronic products, such as mobile phones, laptops, tablet computers, personal digital assistants, and portable electronic devices, to achieve identity recognition. Through fingerprint sensing, users can easily identify their identities. Users only need to place their fingers on the fingerprint sensing panel or area to log in to the electronic device without having to enter a long and cumbersome user name and password.

[0003] Fingerprint, Touch and Display Integration (FTDI) circuits are usually used to process fingerprint sensing functions on display screens. Under the optical fingerprint sensing mechanism, the panel can emit light during the fingerprint sensing period. When a finger touches the panel, the light can be reflected by the touching finger and received by a photodiode arranged on the panel. The reflected light includes the peak and valley information of the fingerprint, thereby generating a voltage signal carrying the fingerprint information. Then, the fingerprint sensor can transmit this voltage signal to the fingerprint touch display integration circuit. Subsequently, the fingerprint touch display integration circuit can process the voltage signal of the fingerprint sensing to amplify the signal and convert it into digital data. The digital image data is then transmitted to a host end, which may include an algorithm for performing fingerprint image recognition based on the received image data, thereby completing the fingerprint recognition process. Under the in-display fingerprint sensing mechanism, the fingerprint sensor may include multiple photodiodes distributed under the entire screen, so that the fingerprint image can be sensed at any position on the screen.

[0004] The fingerprint sensor set on the panel should be realized by the Thin-Film Transistor (TFT) process. Generally speaking, compared with the Complementary Metal Oxide Semiconductor (CMOS) process commonly used in Integrated Circuits (ICs), the efficiency of the thin-film transistor process is usually poor. In addition, under the trend of large-size panels, the parasitic capacitance on the sensing line used to transmit the voltage signal becomes larger and larger, causing the settling time required to drive the sensing line to reach the target voltage to gradually increase.

[0005] In addition, in order to effectively control the cost of the fingerprint touch display integrated circuit, the number of ports of the fingerprint touch display integrated circuit needs to be limited. In this case, a large number of sensing pixels on a large-size panel should be divided into multiple areas, and an input / output port (I / O pin) can be connected to multiple areas, and the fingerprint touch display integrated circuit reads out the voltage signals of different areas respectively in a time-sharing manner. In order to read out the voltage signal from a sensing pixel, current can be supplied to the corresponding sensing line to charge the parasitic capacitance on the sensing line. However, the larger parasitic capacitance on the large-size panel requires more charging time to stabilize the sensing line to the target voltage. In addition, under the time-sharing mechanism, the sensing line needs to be charged every time the fingerprint touch display integrated circuit switches to read out the sensing pixel of the corresponding area, which increases the time consumed by fingerprint recognition, thereby reducing the user experience. In view of this, the existing technology really needs to be improved. Summary of the invention

[0006] Therefore, the main purpose of the present invention is to provide a novel fingerprint sensing system to solve the above problems.

[0007] An embodiment of the present invention discloses an image sensing system, which includes a panel and an image sensing circuit. The panel includes a plurality of sensing pixels, a plurality of sensing lines, and at least one first current source, wherein each sensing line is coupled to a column of sensing pixels among the plurality of sensing pixels, and each first current source is coupled to one of the plurality of sensing lines. The image sensing circuit is coupled to the panel and includes at least one second current source, wherein each second current source is coupled to one of the plurality of sensing lines. A first sensing line among the plurality of sensing lines is coupled to a first current source among the at least one first current source, and is coupled to a second current source among the at least one second current source.

[0008] Another embodiment of the present invention discloses an image sensing circuit coupled to a panel. The panel has a plurality of sensing pixels, a plurality of sensing lines, and at least one first current source, wherein the plurality of sensing lines are coupled to the plurality of sensing pixels, and the at least one first current source is coupled to the plurality of sensing lines. The image sensing circuit includes at least one second current source, wherein each second current source is coupled to one of the plurality of sensing lines on the panel. A first sensing line among the plurality of sensing lines is coupled to a first current source among the at least one first current source, and is coupled to a second current source among the at least one second current source. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 FIG. 4 is a schematic diagram of an image sensing system according to an embodiment of the present invention.

[0010] Figure 2 The schematic diagram is a diagram showing that sensing pixels and sensing lines on a panel are arranged in multiple regions.

[0011] Figure 3 is a schematic diagram of an image sensing system.

[0012] Figure 4 is a schematic diagram of another image sensing system.

[0013] Figure 5 FIG. 4 is a schematic diagram of an image sensing system according to an embodiment of the present invention.

[0014] Figure 6 and 7 A timing diagram for reading out a row of sensing pixels located in different areas according to an embodiment of the present invention.

[0015] Fig. 8A and 8B A schematic diagram of simulation results regarding noise level in an example image frame.

[0016] Fig. 9 FIG. 4 is a schematic diagram of another image sensing system according to an embodiment of the present invention.

[0017] Fig.10 for Fig. 9 The timing diagram for reading out a row of sensing pixels in the image sensing system is shown.

[0018] The reference numerals are described as follows:

[0019] 10, 30, 40, 50 Image sensing system

[0020] 102, 302, 402, 502 panels

[0021] 104, 304, 404, 504 Image sensing circuit

[0022] 112 Analog front end circuit

[0023] 114 Analog-to-digital converter

[0024] 200 switch module

[0025] 210, 310, 410, 510 readout circuit

[0026] Vs11~Vs1Y、Vs21~Vs2Y、sensing pixels

[0027] Vs31~Vs3Y

[0028] Z1~Z3 area

[0029] SL1~SL3 sensing lines

[0030] Is, Is1~Is3, Ipre current source

[0031] Cpar parasitic capacitance

[0032] S1~SY、SZ1~SZ3、SZ1B~SZ3B switch

[0033] Vsout1~Vsout3 voltage

[0034] Cs sampling capacitor

[0035] Ssam Sampling Switch

[0036] P0 Stable period

[0037] P1~P3 Readout sub-period DETAILED DESCRIPTION

[0038] Please refer to Figure 1 , Figure 1 FIG. 1 is a schematic diagram of an image sensing system 10 according to an embodiment of the present invention. Figure 1 As shown, the image sensing system 10 includes a panel 102 and an image sensing circuit 104. The panel 102 can be any type of display panel, such as a liquid crystal display (LCD) panel, an organic light-emitting diode (OLED) panel, etc. The panel 102 can include a fingerprint sensor array, which has a large number of sensing pixels distributed under the entire screen to achieve in-display fingerprint sensing, that is, any position on the screen can be sensed. The fingerprint sensor is usually implemented on the substrate of the panel 102 through a thin film transistor (TFT) process. The image sensing circuit 104 can be a fingerprint touch display integration (FTDI) circuit, which can be implemented in an integrated circuit (IC) in a chip. The fingerprint touch display integration circuit can be used to control the fingerprint sensing operation to receive the fingerprint sensing image from the panel 102 and control the display operation of the panel 102. The image sensing circuit 104 may be disposed on a substrate (eg, a flexible printed circuit board (FPC)) and may be connected to the thin film transistor sensor array on the panel 102 through connection lines on the circuit board.

[0039] like Figure 1As shown, during the fingerprint sensing operation, when a finger touch is detected in a specific area of ​​the panel 102, the panel 102 may emit light in the specific area, and the light reflected by the touching finger may be sensed by a photodiode in the thin film transistor sensor to generate a sensing signal, which is then received by the image sensing circuit 104 through the sensing line. In one embodiment, the image sensing circuit 104 includes an analog front-end (AFE) circuit 112 for receiving a voltage signal from the panel 102 and amplifying the voltage signal. The image sensing circuit 104 may also include an analog-to-digital converter (ADC) 114 for converting the voltage signal into digital data, so as to be processed and recognized by a back-end host device or core processor.

[0040] As described above, with the limited number of ports of the image sensing circuit 104 (such as the fingerprint touch display integrated circuit), a large number of sensing pixels on the panel 102 can be separately arranged in multiple areas, and the sensing lines coupled to the sensing pixels located in different areas can share the same input and output port (I / O pin). Figure 2 , Figure 2 FIG. 1 is a schematic diagram showing that sensing pixels and sensing lines on the panel 102 are arranged in multiple regions. Figure 2 As shown, the sensing pixels are arranged in an array, and each sensing line is coupled to a row of sensing pixels. Figure 2 Each sensing pixel in the image sensing circuit 104 is represented as a transistor coupled to a switch, but those skilled in the art should understand that each sensing pixel may also include a photodiode and any other possible components. In order to reduce the number of ports of the image sensing circuit 104, each input and output port of the image sensing circuit 104 is coupled to multiple sensing lines. Therefore, through the control of the switch module 200, the readout operation for receiving fingerprint sensing signals from sensing pixels in different areas can be performed in time division.

[0041] When the image sensing circuit 104 detects a finger touch, it can determine that the finger is placed in a specific area and enable the sensing pixels in this area to perform fingerprint image sensing. If the area of ​​this specific area is small or the area touched by the finger is large, it means that the finger may touch multiple areas at the same time, and the sensing pixels in these areas need to be enabled for fingerprint image sensing. In this case, the image sensing circuit 104 needs to read out voltage signals from these areas. However, the sensing lines coupled to the sensing pixels in different areas share the same input and output ports, and when each sensing line is connected to the input and output ports and the readout circuit 210 (which may be included in Figure 1When the analog front-end circuit is used, sufficient stabilization time is required to charge to its target level (i.e., to charge the parasitic capacitance on the sensing line). Therefore, the time-sharing operation between different regions requires two or more sensing lines to be charged to their target voltages in different time intervals, resulting in more time for fingerprint sensing.

[0042] Please refer to Figure 3 , Figure 3 FIG. 3 is a schematic diagram of an image sensing system 30. Figure 3 As shown, the image sensing system 30 includes a panel 302 and an image sensing circuit 304. The panel 302 may include a plurality of sensing pixels arranged in an array. Figure 3 Only three columns of sensing pixels Vs11-Vs1Y, Vs21-Vs2Y and Vs31-Vs3Y are shown, which are respectively located in three areas Z1-Z3. The sensing pixels Vs11-Vs1Y, Vs21-Vs2Y and Vs31-Vs3Y can share the same input and output port of the image sensing circuit 304, and the fingerprint sensing signals of these sensing pixels Vs11-Vs1Y, Vs21-Vs2Y and Vs31-Vs3Y must be read out through the input and output port in a time-sharing manner. There are three sensing lines SL1-SL3 on the panel 302, which are respectively coupled to the three columns of sensing pixels Vs11-Vs1Y, Vs21-Vs2Y and Vs31-Vs3Y, and these three sensing lines SL1-SL3 are coupled to the same input and output port. The image sensing circuit 304 may include a readout circuit 310 coupled to the input / output port for receiving the fingerprint sensing signal from the panel 302. The readout circuit 310 may include a current source Is for supplying current to charge the sensing lines SL1-SL3 when the sensing signal is read out through the sensing lines SL1-SL3. Figure 3 As shown, each of the sensing lines SL1-SL3 on the panel 302 includes a parasitic capacitor Cpar. The capacitance of the parasitic capacitor Cpar is about tens to hundreds of picofarads, depending on the length of the sensing line and the resolution of the panel 302.

[0043] Generally speaking, the fingerprint sensing signal is read out by scanning the sensing pixels row by row. In detail, in a first period, the switch S1 is turned on to read out the sensing signal from the sensing pixels Vs11, Vs21 and Vs31 in sequence. Under the time-sharing sensing mechanism, the switch SZ1 is turned on in a first sub-period of the first period, so that the readout circuit 310 can read out the sensing signal from the sensing pixel Vs11. In this sub-period, the current source Is can start to charge the parasitic capacitor Cpar on the first sensing line SL1, and also charge the sampling capacitor Cs, and the corresponding voltage on the first sensing line SL1 starts to rise from 0V to its target voltage, which is the voltage Vsout1 received by the readout circuit 310. The charging of the parasitic capacitor Cpar requires a stabilization time to drive the sensing line SL1 to reach the voltage Vsout1.

[0044] Then, in a second sub-period of the first period, the switch SZ2 is turned on, so that the readout circuit 310 can read the sensing signal from the sensing pixel Vs21. In this sub-period, the current source Is can start to charge the parasitic capacitor Cpar on the second sensing line SL2, and also charge the sampling capacitor Cs, and the corresponding voltage on the second sensing line SL2 starts to rise from 0V to its target voltage, which is the voltage Vsout2 received by the readout circuit 310. It should be noted that the current source Is cannot be coupled to the second sensing line SL2 before the start of the second sub-period, so the parasitic capacitor Cpar on the second sensing line SL2 can only be charged after the start of the second sub-period, and the charging of the parasitic capacitor Cpar requires a period of stabilization time to drive the sensing line SL2 to reach the voltage Vsout2. Similarly, in a third sub-period of the first period, the switch SZ3 is turned on, so that the readout circuit 310 can read the sensing signal from the sensing pixel Vs31. In this sub-period, the current source Is can begin to charge the parasitic capacitor Cpar on the third sensing line SL3. The charging of the parasitic capacitor Cpar requires a stabilization time to drive the sensing line SL3 to reach the voltage Vsout3.

[0045] It can be seen that during the fingerprint sensing process, the current source Is in the readout circuit 310 needs to be continuously switched in different sub-periods to charge the parasitic capacitance Cpar on different sensing lines, and each sub-period requires a stabilization time. In this way, when the finger covers the sensing pixels of multiple areas, it takes more time to read the complete fingerprint image.

[0046] Please refer to Figure 4 , Figure 4 FIG. 4 is a schematic diagram of another image sensing system 40. Figure 4As shown, the image sensing system 40 includes a panel 402 and an image sensing circuit 404. Similarly, there are sensing pixels in three regions Z1-Z3 on the panel 402, each region includes a row of sensing pixels, and the three rows of sensing pixels Vs11-Vs1Y, Vs21-Vs2Y and Vs31-Vs3Y can share the same input and output port of the image sensing circuit 404, so the image sensing circuit 404 and its readout circuit 410 can adopt a similar time-sharing readout mechanism to obtain fingerprint sensing signals.

[0047] The difference between the image sensing system 40 and the image sensing system 30 is that in the image sensing system 40, the current source is implemented on the panel 402, while the current source Is of the image sensing system 30 is implemented in the image sensing circuit 304. Figure 4 As shown, the panel 402 includes current sources Is1 - Is3 , wherein each current source is coupled to a sensing line SL1 - SL3 and a row of sensing pixels Vs11 - Vs1Y, Vs21 - Vs2Y or Vs31 - Vs3Y.

[0048] Similarly, the fingerprint sensing signal is read out by scanning the sensing pixels row by row. Since each sensing line is coupled to a current source Is1-Is3, the parasitic capacitor Cpar can be pre-charged before its corresponding sensing signal is output to the readout circuit 410 of the image sensing circuit 404. For example, during the first period, the switch S1 is turned on to scan the sensing pixels of the first row. During a first sub-period of the first period, the switch SZ1 is turned on so that the readout circuit 410 can read the sensing signal from the sensing pixel Vs11. Before the first sub-period, the current source Is1 can be turned on in advance to charge the parasitic capacitor Cpar so that the voltage Vsout1 on the sensing line reaches a predetermined level corresponding to the sensing signal of the sensing pixel Vs11. Therefore, during the readout period of the first sensing line SL1 (i.e., the first sub-period), the switch SZ1 can be turned on to quickly charge the sampling capacitor Cs to its target level, so that the readout circuit 410 can sample the fingerprint sensing signal in a short time. Through a similar operation, the parasitic capacitance Cpar of the second sensing line SL2 and the third sensing line SL3 can be precharged to a target level before the corresponding readout period, so that the fingerprint sensing signal can be read out quickly.

[0049] However, the current sources Is1 to Is3 on the panel 402 are implemented by thin film transistor technology and are disposed on the substrate of the panel 402. According to the characteristics of the thin film transistor technology, the current sources Is1 to Is3 often have a large offset, and the error of their current values ​​may be as high as 20%. Under a large offset, the current values ​​output by the current sources Is1 to Is3 may be different from each other, resulting in a fixed pattern of noise on the fingerprint sensing signal. In other words, the current offset will affect the sensing signal output through the sensing line. It should be noted that although Figure 4 It is shown that each area Z1-Z3 includes only one column of sensing pixels and one sensing line, but each area may actually include hundreds of sensing lines, and each sensing line has an offset value generated based on the current source error. This offset causes the quality of the fingerprint image to deteriorate, thereby reducing the efficiency of fingerprint recognition.

[0050] In contrast, if the current source is implemented by a complementary metal oxide semiconductor (CMOS) process in an integrated circuit, such as Figure 3 For the current source Is shown, the maximum error of the current value is about 3%, which has a relatively high accuracy compared to the current source implemented with the thin film transistor process. Figure 3 The current source in is implemented in the image sensing circuit 304, which may be an integrated circuit included in the chip.

[0051] As described above, in the image sensing system 30, the current source Is implemented in the image sensing circuit 304 has high accuracy, but because the current source Is needs to charge the parasitic capacitor Cpar on the sensing line within a limited readout time, the stabilization speed of the sensing signal is slow. In the image sensing system 40, the parasitic capacitor Cpar can be pre-charged before the readout period of the sensing signal, so that the stabilization speed of the sensing signal is faster, but the accuracy of the current sources Is1 to Is3 of the sensing line is low.

[0052] The embodiment of the present invention has the advantages of the above two image sensing systems. Figure 5 , Figure 5 FIG. 5 is a schematic diagram of an image sensing system 50 according to an embodiment of the present invention. Figure 5As shown, the image sensing system 50 includes a panel 502 and an image sensing circuit 504. The panel 502 may include a plurality of sensing pixels arranged in an array and a plurality of sensing lines SL1-SL3, wherein each sensing line is coupled to a column of sensing pixels. An image sensing signal (such as a fingerprint sensing signal) may be output by the sensing pixel to the image sensing circuit 504 through the sensing lines SL1-SL3. The image sensing circuit 504 may include a plurality of readout circuits, wherein each readout circuit is coupled to an input-output port, and the input-output port may serve as an interface between the sensing lines SL1-SL3 on the panel 502 and the readout circuit 510 of the image sensing circuit 504. It should be noted that the image sensing circuit 504 may include a plurality of readout circuits. For simplicity, Figure 5 Only one readout circuit 510 is shown. Similarly, in the image sensing system 50, the sensing pixels and their associated sensing lines SL1-SL3 can be separately arranged in multiple regions, and the rows of sensing pixels located in different regions share the same input and output ports. Therefore, a time-sharing mechanism can be used to read out the image sensing signals of the sensing pixels located in different regions. The circuit structure of the image sensing system 50 is similar to Figure 3 or Figure 4 The circuit structure of the image sensing system 30 or 40 in the embodiment is similar to that of the image sensing system 30 or 40, so signals or components with similar functions are represented by the same symbols. Similarly, in the image sensing system 50, the image sensing circuit 504 may be an integrated circuit included in a chip and implemented by a complementary metal oxide semiconductor process, while the circuit on the panel 502 is implemented by a thin film transistor process.

[0053] The difference between the image sensing system 50 and the image sensing system 30 or 40 is that in the image sensing system 50, the panel 502 may include a plurality of current sources Is1-Is3, wherein each current source is coupled to a sensing line SL1-SL3 to supply current to the sensing pixels of the corresponding column. In addition, the image sensing circuit 504 may also include a current source coupled to at least one sensing line on the panel 502. Figure 5 As shown, the current source Is is included in the readout circuit 510 and can be coupled to the sensing lines SL1-SL3 through the input and output ports, that is, the sensing lines SL1-SL3 share the same current source Is. As described above, the image sensing circuit 504 may include a plurality of readout circuits, and each readout circuit includes a current source, which is coupled to the corresponding sensing line SL1-SL3 through the corresponding input and output ports.

[0054] Since the panel 502 includes current sources Is1-Is3 and the image sensing circuit 504 includes a current source Is, for each sensing line SL1-SL3, it can be coupled to a current source on the panel 502 and also coupled to a current source of the image sensing circuit 504. These different current sources can be operated in different ways to achieve high-precision current supply while allowing the sensing lines SL1-SL3 to achieve a fast stabilization time. In detail, during the readout period, the current source Is in the image sensing circuit 504 can be used to supply current to provide an accurate current value, and the current sources Is1-Is3 on the panel 502 can be used to supply current before the readout period to pre-charge the parasitic capacitance Cpar on the sensing lines SL1-SL3.

[0055] In one embodiment, the panel 502 may further include switches SZ1-SZ3 and SZ1B-SZ3B to implement charging operation. The sensing lines SL1-SL3 may be coupled to the current source Is through the switches SZ1-SZ3, and may be coupled to the current source Is1-Is3 through the switches SZ1B-SZ3B.

[0056] Please refer to Figure 6 , Figure 6 A timing diagram for reading out a row of sensing pixels located in different areas according to an embodiment of the present invention. Figure 6 The control signals for controlling the switches S1-SY, SZ1-SZ3 and SZ1B-SZ3B on the panel 502 and the control signals for controlling the sampling switch Ssam included in the image sensing circuit 504 are shown. For each control signal, a "high" level (indicated by a slash) is used to turn on the corresponding switch and a "low" level is used to turn off the corresponding switch. Figure 6 As shown, the scanning period of the first row of sensing pixels Vs11-Vs31 includes a stable sub-period P0 and a plurality of readout sub-periods P1-P3. The switch S1 is turned on during the entire scanning period, so that the sensing signals of the first row of sensing pixels Vs11-Vs31 can be read out in sequence. The scanning period starts from the stable sub-period P0, wherein the switches SZ1B-SZ3B are turned on to couple the sensing lines SL1-SL3 to the current sources Is1-Is3 respectively, so that the current sources Is1-Is3 can supply current to the sensing lines SL1-SL3 to charge the parasitic capacitance Cpar on the sensing lines SL1-SL3, and the switches SZ1-SZ3 are turned off. Then, in the subsequent readout sub-periods P1 to P3, the current source Is in the image sensing circuit 504 only needs to provide an accurate current value to correct the sensing voltage signal on the sensing lines SL1 to SL3, and its operation speed is much faster than the operation of charging the sensing line from zero voltage (i.e., charging from the uncharged state of the parasitic capacitance Cpar).

[0057] In detail, the sampling switch Ssam can be turned on during the readout sub-period P1 to P3 to sample the corresponding sensing lines SL1 to SL3 and read out the fingerprint sensing signal. During the readout sub-period P1, the fingerprint sensing signal of the sensing pixel Vs11 in the area Z1 is to be read out. At this time, the switch SZ1 is turned on and the switch SZ1B is turned off to couple the sensing line SL1 to the current source Is that can output an accurate current value, so that the current source Is supplies current to the sensing line SL1 for reading the fingerprint sensing signal. During the readout sub-period P1, the switches SZ2 and SZ3 for the sensing lines in the areas Z2 and Z3 cannot be turned on to avoid affecting the output signal of the area Z1. At this time, the switches SZ2B and SZ3B can be turned on to supply the current required to charge the parasitic capacitance Cpar on the scanning lines SL2 and SL3.

[0058] In the readout sub-period P2, the fingerprint sensing signal of the sensing pixel Vs21 in the area Z2 is to be read out. At this time, the switch SZ2 is turned on and the switch SZ2B is turned off to couple the sensing line SL2 to the current source Is that can output an accurate current value, so that the current source Is supplies current to the sensing line SL2 for reading the fingerprint sensing signal. In the readout sub-period P2, the switches SZ1 and SZ3 for the sensing lines in the areas Z1 and Z3 cannot be turned on to prevent the output signal of the area Z2 from being affected. At this time, the switches SZ1B and SZ3B can be turned on to supply the current required for charging the parasitic capacitors Cpar on the scan lines SL1 and SL3.

[0059] In the readout sub-period P3, the fingerprint sensing signal of the sensing pixel Vs31 in the area Z3 is to be read out. At this time, the switch SZ3 is turned on and the switch SZ3B is turned off to couple the sensing line SL3 to the current source Is that can output an accurate current value, so that the current source Is supplies current to the sensing line SL3 for reading the fingerprint sensing signal. In the readout sub-period P3, the switches SZ1 and SZ2 for the sensing lines in the areas Z1 and Z2 cannot be turned on to prevent the output signal of the area Z3 from being affected. At this time, the switches SZ1B and SZ2B can be turned on to supply the current required for charging the parasitic capacitors Cpar on the scan lines SL1 and SL2.

[0060] In another embodiment, the stabilization sub-period P0 may also be integrated with the first readout sub-period P1 without affecting the efficiency of the image sensing system 50. Figure 7 As shown, the length of the first readout sub-period P1 is long, so that the switch SZ1 can be turned on for a sufficient time to charge the sensing line SL1 to its target voltage level through the current source Is. In this example, the operations of the readout sub-periods P2 and P3 are similar to those of Figure 6 The operation method shown is not repeated here.

[0061] Please refer to Fig. 8Aand 8B , Fig. 8A and 8B A schematic diagram of simulation results regarding noise level in an example image frame. Fig. 8A A frame of fixed pattern noise (FPN) generated by the image sensing system 40 is shown, in which the current of the sensing line is only supplied by the current source on the panel 402, which is realized by the thin film transistor process. As mentioned above, the current value of the thin film transistor process is offset by up to 20%, resulting in a received sensing image showing a fixed pattern noise in the form of vertical lines. Since each current source is used to supply current to a column of sensing pixels, the offset of the current supplied by the current source will produce vertical lines on the image. This fixed pattern noise causes a significant decrease in the quality of the fingerprint image, resulting in the inability to successfully identify the fingerprint. Figure 8B FIG. 5 shows a frame of fixed pattern noise generated by an image sensing system 50, wherein both the panel 502 and the image sensing circuit 504 include a current source for supplying current to the sensing line. In this example, the current source in the image sensing circuit 504 is used during the readout period, which is implemented by a complementary metal oxide semiconductor process, and the maximum offset or error of this current source is within 3%. Therefore, Fig. 8A Compared to the case shown, the fixed pattern noise is greatly reduced.

[0062] It is worth noting that the purpose of the present invention is to provide a fingerprint image sensing system, wherein the sensing line can receive current from the current source in the image sensing circuit, and can also be pre-charged by the current source on the panel. Those skilled in the art can make modifications or changes accordingly, without limitation thereto. For example, in the above embodiment, each sensing line is coupled to the current source on the panel through a switch and coupled to the current source in the image sensing circuit through another switch, so that the control of the current supply can be achieved by controlling the switch. In another embodiment, the switch can also be implemented in other ways, for example, a multiplexer or selector can be used to select the sensing line to be coupled to one of the current sources.

[0063] In addition, in the above embodiment, the panel includes a plurality of current sources and each current source is coupled to a column of sensing pixels and a sensing line. In another embodiment, a current source on the panel may also be shared by a plurality of sensing lines. For example, for columns of sensing pixels and their corresponding sensing lines located in different regions, a first current source on the panel and a second current source in the image sensing circuit may be used to supply current. Since the sensing signals of the columns of sensing pixels may be read out in time division, for each sensing line, the second current source may be used during the readout period, and the first current source may be used for precharging before the corresponding readout period.

[0064] Please refer to Fig. 9 , Fig. 9 FIG. 9 is a schematic diagram of another image sensing system 90 according to an embodiment of the present invention. Fig. 9 As shown, the circuit structure of the image sensing system 90 is similar to that of the image sensing system 50, so signals or components with similar functions are represented by the same symbols. The difference between the image sensing system 90 and the image sensing system 50 is that the sensing lines SL1-SL3 located in the three regions Z1-Z3 share the same current source Ipre of the panel 502. Therefore, each of the sensing lines SL1-SL3 is coupled to the current source Ipre of the panel 502 and is also coupled to the current source Is of the image sensing circuit 504.

[0065] Fig.10 1 shows a timing diagram for reading out a row of sensing pixels in the image sensing system 90. It should be noted that since the sensing lines SL1 to SL3 are connected to the same current source Ipre through switches SZ1B to SZ3B, respectively, the switches SZ1B to SZ3B cannot be turned on at the same time. The current source Is is used for the readout operation in the readout sub-periods P1 to P3, and the current source Ipre is used for pre-charging the parasitic capacitance Cpar on the sensing lines SL1 to SL3 before the corresponding readout sub-period.

[0066] like Fig.10 As shown, the fingerprint sensing signals of the regions Z1 to Z3 can be read out in the readout sub-periods P1 to P3, respectively. Since the readout sub-period P1 is long enough, no pre-charging operation is required, so there is no need to turn on the switch SZ1B and the current source Ipre is not required for the sensing line SL1. Next, the switches SZ2 and SZ3 are turned on in the sub-periods P2 and P3, respectively, so that the current source Is can supply current for the readout operation. Before the sub-periods P2 and P3, the switches SZ2B and SZ3B are turned on, respectively, so that the current source Ipre can supply current for pre-charging.

[0067] In addition, the embodiments of the present invention can be applied to fingerprint image sensing, but should not be limited thereto. As long as there are sensing lines with large parasitic capacitance on the panel, the embodiments of the present invention can be used to achieve image sensing signals with high accuracy, fastness and stability.

[0068] In summary, an embodiment of the present invention provides an image sensing system, such as a fingerprint image sensing system. In the image sensing system, the image sensing circuit can receive a sensing signal from each column of sensing pixels through a sensing line, and the sensing line can be selectively coupled to a current source on a panel or to a current source in the image sensing circuit. During the readout period of reading out the sensing signal, the sensing line is coupled to the current source in the image sensing circuit to receive its current supply. The current source in the image sensing circuit can be implemented by a complementary metal oxide semiconductor process, and can output a high-accuracy current value, thereby generating a more accurate output sensing signal, thereby achieving better fingerprint recognition efficiency. During the stabilization period before the readout period, the sensing line is coupled to the current source on the panel to receive its current supply. The current source on the panel can pre-charge the parasitic capacitance on the sensing line before the sensing signal is read out. Therefore, before the start of the readout period, the sensing line can be pre-charged to a suitable level, which can increase the stabilization speed of reading out the sensing signal from the sensing line, thereby improving the user experience of fingerprint recognition.

[0069] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An image sensing system, comprising: A panel, including: A plurality of sensing pixels; a plurality of sensing lines, wherein each sensing line is coupled to a column of sensing pixels among the plurality of sensing pixels; and at least one first current source, wherein each first current source is coupled to one of the plurality of sensing lines; and An image sensing circuit is coupled to the panel, and the image sensing circuit includes: at least one second current source, wherein each second current source is coupled to one of the plurality of sensing lines; A first sensing line among the plurality of sensing lines is coupled to a first current source among the at least one first current source, and is coupled to a second current source among the at least one second current source.

2. The image sensing system according to claim 1, wherein: Each of the plurality of sensing lines is coupled to one of the at least one first current source and to one of the at least one second current source.

3. The image sensing system according to claim 1, wherein: For a first sensing pixel among the plurality of sensing pixels coupled to the first sensing line, during a readout period of the first sensing pixel, the first sensing line is coupled to the second current source.

4. The image sensing system according to claim 3, wherein: During a stabilization period before the readout period of the first sensing pixel, the first sensing line is coupled to the first current source.

5. The image sensing system according to claim 1, wherein: The first sensing line is coupled to the first current source through a first switch, and is coupled to the second current source through a second switch.

6. The image sensing system according to claim 5, wherein: For a first sensing pixel among the plurality of sensing pixels coupled to the first sensing line, during a readout period of the first sensing pixel, the first switch is turned off and the second switch is turned on.

7. The image sensing system according to claim 6, wherein: Before the readout period of the first sensing pixel, the first switch is turned on and the second switch is turned off.

8. The image sensing system according to claim 1, wherein: The plurality of sensing pixels and the plurality of sensing lines are separately arranged in a plurality of regions, the plurality of regions including a first region and a second region, and the first sensing line located in the first region and the second sensing line located in the second region among the plurality of sensing lines share the same second current source.

9. The image sensing system according to claim 8, wherein: The second current source supplies current to the first sensing line in a first readout period for sensing the first region, and supplies current to the second sensing line in a second readout period for sensing the second region.

10. The image sensing system according to claim 9, wherein: During the first readout period, the second sensing line receives current from one of the at least one first current source.

11. The image sensing system according to claim 1, wherein: The image sensing system is a fingerprint sensing system, and the image sensing circuit is a fingerprint sensing circuit.

12. An image sensing circuit coupled to a panel, the panel having a plurality of sensing pixels, a plurality of sensing lines coupled to the plurality of sensing pixels, and at least one first current source coupled to the plurality of sensing lines, the image sensing circuit comprising: at least one second current source, wherein each second current source is coupled to one of the plurality of sensing lines on the panel; A first sensing line among the plurality of sensing lines is coupled to a first current source among the at least one first current source, and is coupled to a second current source among the at least one second current source.

13. The image sensing circuit according to claim 12, wherein: Each of the plurality of sensing lines is coupled to one of the at least one first current source and to one of the at least one second current source.

14. The image sensing circuit according to claim 12, wherein: For a first sensing pixel among the plurality of sensing pixels coupled to the first sensing line, during a readout period of the first sensing pixel, the first sensing line is coupled to the second current source.

15. The image sensing circuit according to claim 14, wherein: During a stabilization period before the readout period of the first sensing pixel, the first sensing line is coupled to the first current source.

16. The image sensing circuit according to claim 12, wherein: The first sensing line is coupled to the first current source through a first switch, and is coupled to the second current source through a second switch.

17. The image sensing circuit according to claim 16, wherein: For a first sensing pixel among the plurality of sensing pixels coupled to the first sensing line, during a readout period of the first sensing pixel, the first switch is turned off and the second switch is turned on.

18. The image sensing circuit according to claim 17, wherein: Before the readout period of the first sensing pixel, the first switch is turned on and the second switch is turned off.

19. The image sensing circuit according to claim 12, wherein: The plurality of sensing pixels and the plurality of sensing lines are separately arranged in a plurality of regions, the plurality of regions including a first region and a second region, and the first sensing line located in the first region and the second sensing line located in the second region among the plurality of sensing lines share the same second current source.

20. The image sensing circuit according to claim 19, wherein: The second current source supplies current to the first sensing line in a first readout period for sensing the first region, and supplies current to the second sensing line in a second readout period for sensing the second region.

21. The image sensing circuit according to claim 20, wherein: During the first readout period, the second sensing line receives current from one of the at least one first current source.

22. The image sensing circuit according to claim 12, wherein: The image sensing circuit is a fingerprint sensing circuit.

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