Abstract:
A pixel sensor device has a first sensing unit, a second sensing unit, a first control and reading unit, and a second control and reading unit. The first and second sensing units are disposed concentrically. The first and second control and reading units are connected respectively to the first and second sensing units for separately or simultaneously controlling the first and second sensing units to perform sensing. Since the first and second sensing units are formed by a single pixel sensing array and arranged concentrically, only a single focusing element is required to align centers of the first and second sensing units during the manufacturing process. This achieves high focus accuracy and increases precision in recognition. In the applications of fingerprint recognition and pulse measurement, the user only uses a single finger for sensing so that inaccurate focusing resulted from moving finger is avoided.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to an active pixel sensor device and the operating method thereof In particular, the invention relates to a pixel sensor device using a single pixel sensing array to provide different applications. 
         [0003]    2. Description of Related Art 
         [0004]    There are two types of optical sensor devices for fingerprint recognition. One is the passive pixel sensor (PPS) device, and the other is the active pixel sensor (APS) device. In both types of pixel sensor devices, fingerprint recognition is carried out by resetting sensing pixels of the pixel sensor device, exposing the sensing pixels, reading sensing currents of the sensing pixels, and converting the sensing currents into corresponding sensing voltages. However, in addition to the fingerprint recognition function, there are many other optical sensing applications, such as detecting ambient brightness and detecting pulses. The pulse detection is performed by detecting the contraction and expansion of micro blood vessels. The resolution required by such application is lower than that required by fingerprint recognition. 
         [0005]    To integrate the above-mentioned two applications, the optical sensor device usually has an APS device and a photo sensor device. As shown in  FIG. 7 , the APS device  60  includes an active pixel sensing array  601 , a reset and selection circuit  61 , and a signal reading circuit  62 . Before the active pixel sensing array  601  has an exposure, the reset and selection circuit  61  resets each sensing pixel P 11 ˜Pmn on the active pixel sensing array  601  in sequence, then exposes the active pixel sensing array  601 . After the exposure is complete, the reset and selection circuit  61  selects the sensing pixels in a row, and the signal reading circuit  62  reads sensing voltages corresponding to the sensing currents. The photo sensor device  70  includes a photo sensing array  701  and a signal reading circuit  72 . The sensing pixels of the photo sensor array  701  have a relative larger photo sensing area. Therefore, after the photo sensor array  701  is reset and exposed, the sensing current detected by the signal reading circuit  72  is converted into a corresponding sensing voltage. The sensing voltage is used to determine the intensity of the ambient brightness or the variation in the contraction and expansion of micro blood vessels on a finger. 
         [0006]    Accordingly, to integrate two or more different applications, the optical sensor device has to use two different sensors, such as the active pixel sensing array  601  and the photo sensing array  701 . Moreover, the two different sensing arrays have different circuit designs, and result in increasing both the cost and size of the entire device. In the example of having fingerprint recognition and pulse measurements, the user needs to place his finger on different regions corresponding to the different sensors for different purposes. Such operation is not convenient. 
         [0007]    Moreover, such a dual-application optical sensor device has the active pixel sensing array  601  and the photo sensing array  701  formed in different regions. If only a single focusing element is used, it is difficult to have a precise focus because the active pixel sensing array  601  and the photo sensing array  701  are not in the same region. If two focusing elements are used for the active pixel sensing array  601  and the photo sensing array  701 respectively, the cost becomes higher and the control circuit gets more complicated. 
       SUMMARY OF THE INVENTION 
       [0008]    An objective of the invention is to provide a pixel sensor device using a single pixel sensing array to provide several different applications. 
         [0009]    To achieve the above-mentioned objective, the active pixel sensor device includes: 
         [0010]    a first sensing unit including a plurality of first sensing pixels; 
         [0011]    a second sensing unit including a plurality of second sensing pixels, wherein the first sensing pixels are disposed around an outer edge of the second sensing pixels and the first and second sensing units are disposed concentrically; 
         [0012]    a first signal reading unit connecting to all the first sensing pixels for detecting a summation of sensing currents flowing through all the first sensing pixels; and 
         [0013]    a second control and reading unit connecting to each second sensing pixel for reading individually a sensing voltage of each second sensing pixel. 
         [0014]    The first and second sensing units of the pixel sensor device all exist on a single pixel sensing array. The first signal reading unit and the second control and reading unit can perform detections separately or simultaneously, thereby implementing two different applications. Since the first and second sensing units are configured concentrically, only a single focusing element is required to focus at the center of the first and second sensing units in the fabrication. This can achieve accurate focusing and increase the precision in recognition. For the dual applications of fingerprint recognition and pulse measurement, the user only needs to use one finger. This avoids the problem of imprecise measurements as a result of being out of focus as the user moves fingers. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1A  is a circuit block diagram of the pixel sensor device of the invention; 
           [0016]      FIG. 1B  is another circuit block diagram of the pixel sensor device of the invention; 
           [0017]      FIG. 2A  is a detailed circuit diagram of part of the first sensing unit and the first signal reading unit in the first embodiment of the invention; 
           [0018]      FIG. 2B  is another detailed circuit diagram of part of the first sensing unit and the first signal reading unit in the first embodiment of the invention; 
           [0019]      FIG. 3  is a detailed circuit diagram of part of the second sensing unit in the first embodiment of the invention; 
           [0020]      FIG. 4A  is a detailed circuit diagram of part of the first sensing unit and the first signal reading unit in the second embodiment of the invention; 
           [0021]      FIG. 4B  is another detailed circuit diagram of part of the first sensing unit and the first signal reading unit in the second embodiment of the invention; 
           [0022]      FIG. 5  is yet another circuit block diagram of the pixel sensor device; 
           [0023]      FIG. 6  is a flowchart of the operating method of the pixel sensor device; and 
           [0024]      FIG. 7  is a circuit block diagram of a conventional optical sensor device that integrates two applications. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0025]    This invention proposes a pixel sensor device. It uses the design of a single pixel sensing array that can separately or simultaneously support different applications. The contents of the invention are explained in example of following embodiments. 
         [0026]    With reference to  FIG. 1A , the pixel sensor device includes a first sensing unit  11 , a second sensing unit  12 , a first control and reading unit  20 , and a second control and reading unit  30 . 
         [0027]    The first and second sensing units  11 ,  12  are formed by a single pixel sensing array  10 . The first sensing unit  11  includes a plurality of first sensing pixels  111  disposed annularly and indicated by the white squares. The second sensing unit  12  also includes a plurality of second sensing pixels  121  indicated by the gray squares. All of the first sensing pixels  111  surround the second sensing unit  12 , so that the first sensing unit  11  and the second sensing unit  12  are concentric. As shown in  FIG. 1A , the first sensing unit  11  has an annular square shape. The second sensing pixels  121  of the second sensing unit  12  are disposed in a matrix shape. Alternatively, as shown in  FIG. 1B , the first sensing unit  11  has a square outer shape and an approximate circular inner shape. Therefore, the second sensing unit  12  is disposed in an approximate circular shape for making corresponding detections. Therefore, the first and second sensing units  11 ,  12  are also concentric. In this embodiment, the pixel sensing array  10  has m rows and n columns. The second sensing unit  12  includes pixels between the third row and the (m-2)th row and between the third column and the (n-2)th column. The other pixels belong to the first sensing unit  11 . 
         [0028]    The first control and reading unit  20  connects to all the sensing pixels  111  of the first sensing unit  11  for detecting a current sum Isum, i.e. a summation of sensing currents flowing through all the first sensing pixels  111  of the first sensing unit  11 . The first control and reading unit  20  further converts the current sum Isum into an output signal, which can be an output voltage or output current. 
         [0029]    The second control and reading unit  30  connects to all the sensing pixels  121  of the second sensing unit  12  for reading a sensing signal, such as a sensing voltage, of each second sensing pixel  121  of the second sensing unit  12 . 
         [0030]    The following example uses two embodiments with pixel sensing arrays  10  using different sensing pixels to explain the detailed circuit diagrams and circuit actions of the first and second control and reading units  20 ,  30 . 
         [0031]      FIG. 1A  is a circuit block diagram of a pixel sensor device.  FIG. 2A  is a detailed circuit diagram of part of the first sensing unit  11  and the first signal reading unit  22  in  FIG. 1A .  FIG. 3  is a detailed circuit diagram of part of the second sensing unit  12  in  FIG. 1A . As shown in  FIGS. 1A ,  2 A, and  3 , the first and second sensing pixels  111 ,  121  of the first and second sensing units  11 ,  12  are all active sensing pixels. The active sensing pixels, such as the pixels P 11 , P 33 , may have the 3T-APS (active pixel sensor) structure. The pixels P 11 , P 33  represent respectively the circuit structures of the first sensing pixel  111  and the second sensing pixel  121 . Each of the first and second sensing pixels  111 ,  121  includes a power terminal P, a reset terminal R, a selection terminal S, and an output terminal O. Each of the sensing pixels includes a reset switch M 11   a,  M 33   a,  a source follower M 11   b,  M 33   b,  a selection switch M 11   c,  M 33   c,  and a photo detector PD. The reset switch M 11   a,  M 33   a  is a metal-oxide-semiconductor field-effect transistor (MOSFET) that includes a drain connecting to the power terminal P, a gate connecting to the reset terminal R, and a source connecting to the photo detector PD. The source follower M 11   b,  M 33   b  can also be a MOSFET that includes a drain connecting to an operating power Va, a gate connecting to the source of the reset switch M 11   a,  M 33   a,  and a source connecting to the selection switch M 11   e,  M 33   c.  The selection switch M 11   c,  M 33   c  can also be a MOSFET which includes a drain connecting to the source of the source follower M 11   b,  M 33   b,  a gate connecting to a selection terminal S, and a source connecting to the output terminal O. The source of the selection switch M 11   c  of the first sensing pixel  111  can have no connection (NC), as shown in  FIGS. 2A and 2B , or connect to the second control and reading unit  30 , and both connection configurations do not affect the function of the first sensing pixel  111 . The output terminal O of the selection switch M 33   c  of the second sensing pixel  121  (as shown in  FIG. 3 ) connects to a voltage output terminal Vo 3  of the second control and reading unit  30 . A cathode of the photo detector PD connects to the source of the reset switch M 11   a,  M 33   a.  An anode of the photo detector PD connects to a ground terminal The photo detector PD obtains charges after the reset switch M 11   a,  M 33   a  becomes conductive. Under the exposure of light, the charges of the photo detector PD decline at a rate with a positive correlation to the intensity of the light source. Besides, each of the active sensing pixels may have the 4T-APS structure rather than limited to the 3T-APS structure. In the first sensing unit  11  and the second sensing unit  12 , the reset terminals R of the pixels in the same row are connected together, and the selection terminals S of the pixels in the same row are connected together. In the second sensing unit  12 , the output terminals O of the pixels in the same column are connected together and to the corresponding voltage output terminals Vo3˜Vo(n-2) of the second control and reading unit  30 . 
         [0032]    With reference to  FIGS. 1A and 2A , the power terminals P of all the pixels in the first sensing unit  11  connect to a measuring terminal M. The first control and reading unit  20  includes a first reset and selection unit  21 , which has a plurality of reset terminals R 1  to Rm connecting respectively to the switches of the first sensing pixels  111 , so as to output a reset signal to the switches of the first sensing pixels  111  simultaneously. After all the first sensing pixels  111  are exposed to light, the first control and reading unit  20  detects the current sum Isum flowing through all of the first sensing pixels  111  via the measuring terminal M. More explicitly, the first control and reading unit  20  may further include a first signal reading unit  22  that connects to the power terminals P of all first sensing pixels  111  via the measuring terminal M. After converting the detected current sum Isum into an output signal, the first control and reading unit  20  outputs the output signal as optical sensing information. The output signal can be an output voltage or an output current. In a different embodiment, the first reset and selection unit  21  can also provide only one reset terminal R that connects to the reset terminals R of all the first sensing pixels  111  through external conductive wires. 
         [0033]    As shown in  FIG. 2A , the first signal reading unit  22  includes an operational amplifier OP and a resistor R. The work voltage required by the operational amplifier OP can come from the operating power Va or other DC sources. A non-inverting input terminal (+) of the operational amplifier OP connects to a reference voltage Vref, and an inverting input terminal (−) of the operational amplifier OP connects to the power terminals P of the first sensing pixels  111 (i.e., P 11 , P 12 , P 13 ) via the measuring terminal M. The resistor R connects between the inverting input terminal (−) and the output terminal Vout_op of the operational amplifier OP. As shown in  FIG. 2B , the first signal reading unit  22 ′ in another embodiment can also include an operational amplifier OP, a capacitor C, and a switch SW. The work voltage required by the operational amplifier OP can come from the operating power Va or other DC sources. The non-inverting input terminal (+) of the operational amplifier OP connects to a reference voltage Vref, and the inverting input terminal (−) of the operational amplifier OP connects to the power terminals P of the first sensing pixels  111  via the measuring terminal M. The capacitor C connects between the inverting input terminal (−) and the output terminal Vout_op of the operational amplifier OR The switch SW connects in parallel with the capacitor C. The work power required by each of the first sensing pixels  111  can be the same as the reference voltage Vref of the operational amplifier OP. Due to the fact that the operational amplifier OP is connected to the virtual ground, the inverting input terminal (−) of the operational amplifier OP has a voltage level equivalent to the reference voltage Vref of the non-inverting input terminal (+). 
         [0034]    When the first sensing unit  11  of this embodiment performs the application such as ambient light detection or pulse measurement, the power terminals P of all the first sensing pixels  111  are connected with the inverting input terminal (−) of the operational amplifier OP of the first signal reading unit  22 . The first reset and selection unit  21  outputs a reset signal via the reset terminals R1˜Rm so that the reset switches of all the first sensing pixels  111  become conductive. The photo detector PD is then reversely biased at the voltage Vref, followed by exposure. The photo detectors PD of all the first sensing pixels  111  generate their sensing currents. The operational amplifier OP of the first signal reading unit  22  obtains the current sum Isum from the measuring terminal M, and converts the current sum Isum into an output voltage. The output voltage is output via the output terminal Vout_op of the operational amplifier OP as optical sensing information. Since all the first sensing pixels  111  are simultaneously charged and exposed to light, the invention provides a large optical sensing area for such applications as ambient light detection or pulse measurement. 
         [0035]    With reference to  FIGS. 1A and 3 , the second control and reading unit  30  includes a second reset and selection unit  31  and a second signal reading unit  32 . In this embodiment, the second sensing pixels  121  are also active sensing pixels. The second reset and selection unit  31  has a plurality of reset terminals R3˜Rm-2 connecting respectively to the reset switches of the second sensing pixels  121 (such as P 33 , P 34 , P 35  in  FIG. 3 ) for outputting a reset signal to the switch of each second sensing pixel  121  and outputting a selection signal to the selection terminal S 3  of each second sensing pixels  121 . The voltage output terminals Vo3˜Vo(n-2) of the second signal reading unit  32  connect respectively to the output terminals O of the second sensing pixels  121  in each column for reading the sensing current produced by the stored charges in the photo detectors PD in each of the second sensing pixels  121  in each column due to light exposure, or reading the sensing voltage corresponding to the sensing current. 
         [0036]    The reset terminals R of the second sensing pixels  121  in the same row are connected together, and the selection terminals S thereof are connected together as well. Therefore, the second sensing pixels  121  in the same row can be simultaneously reset and selected. After row sensing data of the sensing pixels  121  in the same row are read out, the row sensing data can be decoded to obtain individual sensing data of the second sensing pixels  121 . Since the decoding technique is well-known to a person skilled in the art, it is not further described herein. In addition to the above-mentioned connection scheme, one can also connect the reset terminal R and the selection terminal S of each of the second sensing pixels  121  separately to the second reset and selection unit  31 , so that the second reset and selection unit  31  can independently reset and select the second sensing pixels  121 . Besides, another feasible scheme is to connect all the second sensing pixels  121  together before further connecting to the second reset and selection unit  31 . Therefore, all of the second sensing pixels  121  are simultaneously reset and selected. After the sensing data of all the second sensing pixels  121  are read out, the sensing data are decoded to obtain individual sensing data of each of the sensing pixels. 
         [0037]    When the second sensing unit  12  of this embodiment performs the application of fingerprint recognition, the second reset and selection unit  31  outputs a reset signal to the reset terminal R of each second sensing pixel (using the second sensing pixel P 33  as an example), thereby resetting the voltage of the photo detector PD. Under light exposure, the photo detector PD generates a sensing current. The second reset and selection unit  31  further outputs the selection signal to the selection terminal S of the second sensing pixel  121  which have been reset, thereby making the selection switch thereof conductive. The second signal reading unit  32  reads the sensing voltages of the voltage output terminals Vo3˜Vo(n-2). Thus the sensing voltage of each second sensing pixel  121  that scans the fingerprint for fingerprint recognition is obtained. 
         [0038]    A second embodiment of the invention is described as follow. As shown in  FIGS. 1A ,  3 , and  4 A, the first sensing pixels  111  of the first sensing unit  11  are passive sensing pixels, and the second sensing pixels  121  of the second sensing unit  12  are active sensing pixels, wherein the second sensing pixels  121  are the same as the first embodiment and are not further described here. The passive sensing pixel includes a power terminal P, a reset terminal S, a reset switch M 11 , and a photo detector PD. The reset switch M 11  can be a MOSFET that includes a drain connecting to the power terminal S, a gate connecting to the reset terminal R (taking the first sensing pixel P 11  as an example), and a source connecting to the cathode of the photo detector PD. The anode of the photo detector PD connects to a ground terminal. Therefore, the photo detector PD obtains charges when the reset switch M 11  becomes conductive, and the charges decline at a rate with a positive correlation to the intensity of the light source. Besides a passive sensing pixel, each of the first sensing pixels  111  of the first sensing unit  11  in another embodiment can be a photo detector PD without the reset switch M 11 . The cathode of the photo detector PD connects to the power terminals P of the first sensing pixels  111  in order to connect to the first signal reading unit  22 . Under this structure, the first reset and selection unit  21  in  FIG. 1A  is not required. 
         [0039]    The first control and reading unit  20  in this embodiment is the same as that in the first embodiment. That is, the first control and reading unit  20  includes a first reset and selection unit  21  or further includes first signal reading units  22 ,  22 ′. The first signal reading units  22 ,  22 ′ are shown in  FIGS. 4A and 4B  and are the same as those in  FIGS. 2A and 2B . Therefore, they are not further described here again. 
         [0040]    When the first sensing unit  11  of this embodiment performs such an application as ambient light detection or pulse measurement, the power terminals P of all the first sensing pixels  111  connect to the inverting input terminal (−) of the operational amplifier OP of the first signal reading unit  22 . The first reset and selection unit  20  outputs the reset signal to the reset terminals R of all the first sensing pixels  111 , so that the photo detectors PD are biased at the voltage Vref. After exposure to light, the photo detectors PD of all the first sensing pixels  111  produce sensing currents. The operational amplifier OP of the first signal reading unit  22  obtains a current sum Isum, i.e. a summation of the sensing currents, converts the current sum Isum into an output voltage, and outputs the output voltage via the output terminal Vout_op of the operational amplifier OP as optical sensing information. Since all the first sensing pixels  111  are simultaneously charged and exposed to light, a larger optical sensing area is achieved to detect the intensity of ambient brightness or to measure pulses by detecting the contraction and expansion of finger blood capillaries. The application of fingerprint recognition by the second sensing unit  12  is the same as that in the first embodiment. 
         [0041]    It is clear from the above description that the first and second reset and selection units  21 ,  31  in either the first embodiment or the second embodiment are connected respectively to the first and second sensing pixels  111 ,  121  and have the same functions. Therefore, as shown in  FIG. 5 , the first and second reset and selection units  21 ,  31  can be further integrated into a single reset and selection unit  40 . 
         [0042]    With reference to  FIG. 6 , the operating method of the active pixel sensor device can be summarized into one operating in the first mode S 10  and the other operating in the second mode S 20 . Under the first mode, the method includes the steps of: driving the first sensing pixels (step S 11 ); and measuring the measuring terminal to obtain a summation of sensing currents flowing through all of the first sensing pixels (step S 12 ). Under the second mode, the method includes the steps of: driving each second sensing pixel (step S 21 ); and measuring individually the sensing signal of each second sensing pixel (step S 22 ). 
         [0043]    The first sensing unit  11  and the second sensing unit  12  of the invention are disposed concentrically. Not only does this scheme save the area in manufacturing, only a single focusing element is required to focus at the center of the first sensing unit  11  and the second sensing unit  12 . This can readily achieves the effect of focusing accurately and increasing the resolution of recognition. 
         [0044]    When making the sensing pixels for fingerprints recognition, such as the second sensing pixels  121  of the second sensing unit  12 , the surrounding of these sensing pixels is formed with several dummy pixels to ensure the symmetry property of the sensing pixels for fingerprints recognition. Therefore, the invention can directly use the dummy pixels as the first sensing pixels  111 . In this case, the original dummy pixels become useful and have the function of detection, supporting different applications (e.g., the above-mentioned ambient light detection or pulse measurement) without purposely making additional sensing pixels. 
         [0045]    In summary, the invention divide the pixel sensing array into the first and second sensing units disposed concentrically in order to perform sensing by the first and second control and reading units. The first control and reading unit connects to all the first sensing pixels and, therefore, can detect the summation of sensing currents flowing through all the sensing pixels, thereby realizing large-area sensing. The second control and reading unit reads individually the second sensing pixels of the second sensing unit for implementing high-resolution fingerprint recognitions. Consequently, the invention only requires a single pixel sensing array to provide applications of high-resolution fingerprint recognitions integrated with ambient light or pulse measurement. It has the advantage of lower cost, simpler circuit, and smaller size. The user only needs to place his finger at the pixel sensing array, relatively easy in use. The first and second sensing units are disposed concentrically. When the user puts a single finger for measurement, the invention can avoid the problem of imprecise measurements as a result of being out of focus as the user moves fingers. 
         [0046]    The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.