Patent Publication Number: US-8119966-B2

Title: Solid-state image pickup device suppressing power consumption in case of increase in imaging pixels or speed by controlling imaging A/D converting circuit by signal from low power triggering A/D converting circuit

Description:
TECHNICAL FIELD 
     The present invention relates to a solid-state image pickup device having an imaging region in which a plurality of pixels respectively including photodiodes that each generate electric charge of an amount according to an incident light amount are arranged two dimensionally. 
     BACKGROUND ART 
     A solid-state image pickup device includes an imaging region in which a plurality of pixels respectively including photodiodes are arranged two dimensionally. Further, in some cases, the solid-state image pickup device includes an A/D converting circuit that outputs a digital value according to an amount of electric charge generated in a photodiode of each pixel. In such a solid-state image pickup device, the number of pixels is ever-increasing, and further, the speeding-up of imaging has been demanded. Such an increase in the number of pixels and speeding-up of imaging generally bring about an increase in power consumption of the solid-state image pickup device. 
     Patent Document 1: Japanese Translation of International Application Kohyo) No. 2002-505002 
     DISCLOSURE OF THE INVENTION 
     Problem to be Solved by the Invention 
     Meanwhile, depending on the usage of a solid-state image pickup device, attempts have been made to suppress an increase in power consumption, or attempts have been made to preferably reduce power consumption in some cases. For example, there are cases in which attempts have been made to drive the solid-state image pickup device with a battery over a long period of time, attempts have been made to suppress heat generation due to the configuration of an apparatus including the solid-state image pickup device, and the like. The present invention has been made in order to solve the above problem, and an object thereof is to provide a solid-state image pickup device capable of suppressing an increase in power consumption even if the intention is to increase the number of pixels or speed up imaging. 
     Means for Solving the Problem 
     A solid-state image pickup device according to the present invention includes: (1) an imaging region which includes a plurality of pixels each having a photodiode that generates electric charge of an amount according to an incident light amount and a charge storing section storing the electric charge, the imaging region stores electric charge generated in the photodiode in each of the plurality of pixels by the charge storing section during a period instructed by a controlling signal of a charge storing operation; (2) a triggering photosensitive region which includes a triggering photodiode that generates electric charge of an amount according to an incident light, amount; and (3) an output section that outputs a digital value (hereinafter, referred to as “pixel data”) according to the amount of electric charge stored in the charge storing section in each of the plurality of pixels after the period instructed by the controlling signal of the charge storing operation, and outputs a digital value hereinafter, referred to as “triggering data”) according to the amount of electric charge generated in the triggering photosensitive region during a period when the pixel data is not output. Moreover, the output section included in the solid-state image pickup device operates with lower power consumption at the time of outputting the triggering data as compared with the time of outputting the pixel data. Further, the output section preferably operates at a lower speed or with a smaller number of output bits at the time of outputting the triggering data as compared with the time of outputting the pixel data. 
     In the solid-state image pickup device according to the present invention, each of the plurality of pixels included in the imaging region has a photodiode that generates electric charge of an amount according to an incident light amount and a charge storing section that stores the electric charge. The electric charge generated in the photodiode in each of the plurality of pixels are stored by the charge storing section during a period instructed by a controlling signal of a charge storing operation. On the other hand, electric charge of an amount according to an incident light amount is generated in the triggering photodiode included in the triggering photosensitive region. After the period instructed by the controlling signal of the charge storing operation, a digital value pixel data) according to the amount of electric charge stored in the charge storing section in each of the plurality of pixels is output from the output section. Further, during a period when the pixel data is not output from the output section, a digital value (triggering data) according to the amount of electric charge generated in the triggering photosensitive region is output from the output section. 
     In this way, the period when the pixel data is output and the period when the triggering data is output are distinguished from one another. Then, the output section operates with lower power consumption at the time of outputting the triggering data as compared with the time of outputting the pixel data. Further, the output section operates at a lower speed or with a smaller number of output bits, which enables the output section to operate with lower power consumption. 
     In the solid-state image pickup device according to the present invention, it is preferable that the output section includes an imaging A/D converting circuit that performs an A/D converting operation to output the pixel data after the period instructed by the controlling signal of the charge storing operation, and a triggering A/D converting circuit that outputs the triggering data, and the triggering A/D converting circuit operates with lower power consumption as compared with the imaging A/D converting circuit. In this case, during the period when the pixel data is output from the output section, the imaging A/D converting circuit operates, and the triggering A/D converting circuit is suspended. On the other hand, during the period when the triggering data is output from the output section, the triggering A/D converting circuit operates, and the imaging A/D converting circuit is suspended. 
     In the solid-state image pickup device according to the present invention, it is preferable that the output section outputs the pixel data and the triggering data to a common output signal line. In this case, because the pixel data and the triggering data are output from the output section to the common output signal line in a time-division-multiplexed manner, a small number of wirings for inputting and outputting signals and the like with an external device may be sufficient, and when the solid-state image pickup device possesses higher reliability in use in X-ray imaging in an oral cavity, for example. In addition, it is preferable that the pixel data and the triggering data output from the output section to the common output signal line are serial data. 
     It is preferable that the solid-state image pickup device according to the present invention further includes a controlling section to which the triggering data output from the output section is input, and generates the controlling signal of the charge storing operation, which is instructing each of the plurality of pixels in the imaging region to perform a charge storing operation when an absolute value of the triggering data is greater than a threshold value. In this case, the controlling signal of the charge storing operation is automatically generated by the controlling section on the basis of the triggering data output from the output section. 
     In the solid-state image pickup device according to the present invention, it is preferable that the triggering photosensitive region includes one triggering photodiode provided so as to surround the imaging region. Moreover, it is also preferable that the triggering photosensitive region includes a plurality of triggering photodiodes which are provided around the imaging region so as to be connected to one another. By thus forming the triggering photosensitive region, light incidence into the solid-state image pickup device can be detected with high sensitivity. 
     Effects of the Invention 
     The solid-state image pickup device according to the present invention is capable of suppressing an increase in power consumption even when an attempt is made to increase the number of pixels or speed up imaging. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a configuration diagram of a solid-state image pickup device  1  according to the present embodiment. 
         FIG. 2  is a configuration diagram of an output section  60  included in the solid-state image pickup device  1  according to the present embodiment. 
         FIG. 3  is a diagram showing the respective circuit configurations of a pixel P m,n  and a holding circuit H n  included in the solid-state image pickup device  1  according to the present embodiment. 
         FIG. 4  is a diagram showing the circuit configuration of a differential operating circuit  61  included in the solid-state image pickup device  1  according to the present embodiment. 
         FIG. 5  is a diagram showing the circuit configuration of an integrating circuit  62  included in the solid-state image pickup device  1  according to the present embodiment. 
         FIG. 6  is a timing chart showing an example of operations of the solid-state image pickup device  1  according to the present embodiment. 
         FIG. 7  is a schematic plan view of the solid-state image pickup device  1 . 
         FIG. 8  is a sectional view taken along arrow VIII-VIII of a triggering photosensitive region  20  shown in  FIG. 7 . 
         FIG. 9  is a schematic plan view of the solid-state image pickup device  1 . 
         FIG. 10  is a circuit diagram showing an electrical connection relationship among triggering photodiodes TD in the triggering photosensitive region  20  shown in  FIG. 9 . 
     
    
    
     DESCRIPTION OF SYMBOLS 
       1  Solid-state image pickup device 
       10  Imaging region 
       20  Triggering photosensitive region 
       30  Row selecting section 
       40  Column selecting section 
       50  Voltage holding section 
       60  Output section 
       61  Differential operating circuit 
       62  Integrating circuit 
       63  Imaging A/D converting circuit 
       64  Triggering A/D converting circuit 
       70  Controlling section 
     P 1,1 -P M,N  Pixels 
     BEST MODES FOR CARRYING OUT THE INVENTION 
     Hereinafter, a best mode for carrying out the present invention will be described in detail with reference to the accompanying drawings. Here, in the description of the drawings, identical elements are designated with identical numerical symbols so as to avoid overlapping descriptions. 
       FIG. 1  is a configuration diagram of a solid-state image pickup device  1  according to the present embodiment. The solid-state image pickup device  1  shown in this drawing includes an imaging region (an imaging photodetecting section)  10 , a triggering photosensitive region (a triggering photodetecting section)  20 , a row selecting section  30 , a column selecting section  40 , a voltage holding section  50 , an output section  60 , and a controlling section  70 . In addition, in this drawing, wirings among elements are omitted or simplified. 
     The imaging region  10  is a region for taking an image of incident light, and includes pixels P 1,1 , to P M,N  arrayed two dimensionally in M rows and N columns. A pixel P m,n  is located in the m-th row and the n-th column. The M×N pixels P 1,1  to P M,N  have a common configuration, and each of those includes a photodiode that generates electric charge of an amount according to the incident light amount and a charge storing section that stores the electric charge. The imaging region  10  stores the electric charge generated in the photodiode in each of the M×N pixels P 1,1  to P M,N  by the charge storing section during a period instructed by a controlling signal of the charge storing operation, which is output from the controlling section  70 . Where M and N are integers greater than or equal to 2, m is an integer greater than or equal to 1 and less than or equal to M, and n is an integer greater than or equal to 1 and less than or equal to N. 
     The triggering photosensitive region  20  is a region for sensing light incidence, and includes a triggering photodiode that generates electric charge of an amount according to the incident light amount. The number and the arrangement of the triggering photodiodes included in the triggering photosensitive region  20  may be made in various modes. However, in order to sense light incidence with high sensitivity, it is preferable that the triggering photodiodes are provided so as to surround the imaging region  10 , and also the photodetecting area is wide. 
     It is preferable that the triggering photosensitive region  20  includes one triggering photodiode TD provided so as to surround the imaging region  10  as shown in the drawing (refer to  FIG. 8 ). 
       FIG. 7  is a schematic plan view of the solid-state image pickup apparatus  1 , and the imaging region  10  is set in the center of a semiconductor substrate  100 , and the triggering photosensitive region  20  is provided so as to surround the imaging region  10 . 
       FIG. 8  is a sectional view taken along arrow VIII-VIII of the triggering photosensitive region  20  shown in  FIG. 7 . A P-type semiconductor region  101  is formed at the surface side of an N-type semiconductor substrate  100 , and the surface of the semiconductor substrate  100  is covered with an insulating layer  102 , and an upper electrode  103  contacts the P-type semiconductor region  101  via a contact hole provided in the insulating layer  102 . A lower electrode  104  is provided on the back surface of the semiconductor substrate  100 . A PN junction is formed on the interface between the P-type semiconductor region  101  and the N-type semiconductor substrate  100 , and these constitute one triggering photodiode TD. That is, the P-type semiconductor region  101  continuously surrounds the circumference of the imaging region  10 . 
     It is also preferable that the triggering photosensitive region  20  includes a plurality of triggering photodiodes TD provided around the imaging region  10  so as to be connected to one another in parallel (refer to  FIG. 9 ). 
       FIG. 9  is a schematic plan view of the solid-state image pickup apparatus  1 , and the imaging region  10  is set in the center of the semiconductor substrate  100 , and the triggering photosensitive region  20  is provided so as to surround the imaging region  10 . A sectional view taken along arrow VIII-VIII of the triggering photodiodes TD in the triggering photosensitive region  20  shown in  FIG. 9  is the same as that shown in  FIG. 8 . 
       FIG. 10  is a circuit diagram showing an electrical connection relationship among the triggering photodiodes TD in the triggering photosensitive region  20  shown in  FIG. 9 . The anodes of the triggering photodiodes TD are connected with a common wiring formed of the upper electrode  103 , and the cathodes thereof are grounded via a common electrode formed of the lower electrode  104 . 
     Description of the present invention will be continued with reference to  FIG. 1  again. The row selecting section  30  sequentially designates the respective rows in the imaging region  10  to output a voltage value according to an amount of electric charge stored in the charge storing section in each of the N pixels P m,1  to P m,N  in the designated m-th row to the voltage holding section  50  under control of the controlling section  70 . The row selecting section  30  includes an M-staged shift register circuit, and is capable of sequentially designating each row in the imaging region  10  by an output bit at each stage of this shift register circuit. 
     The voltage holding section  50  includes N holding circuits H 1  to H N  having a common configuration. The holding circuit H n  is connected to the M pixels P 1,n  to P M,n  in the n-th column in the imaging region  10 , and a voltage value output from one pixel P m,n  of the pixels is input thereto, and the voltage holding section  50  holds and outputs the input voltage value. The holding circuit H n  is capable of not only holding a voltage value indicating a signal component superimposed with a noise component but also holding a voltage value indicating a noise component. 
     The column selecting section  40  sequentially designates the N holding circuits H 1  to H N  included in the voltage holding section  50  to output a voltage value held by the designated n-th holding circuit H n  to the output section  60 . The column selecting section  40  includes an N-staged shift register circuit, and is capable of sequentially designating the N holding circuits H 1  to H N  by an output bit at each stage of this shift register circuit. 
     The output section  60  outputs a digital value (pixel data) according to the amount of electric charge stored in the charge storing section in each of the M×N pixels P 1,1  to P M,N  after a period instructed by the controlling signal of the charge storing operation, which is output from the controlling section  70  (i.e., a period in which electric charge generated in the photodiode in each pixel P m,n  is stored in the charge storing section). Further, the output section  60  outputs a digital value (triggering data) according to the amount of electric charge generated in the triggering photosensitive region  20  during a period in which the pixel data is not output. The output section  60  operates with lower power consumption at the time of outputting the triggering data as compared with the time of outputting the pixel data. 
     It is preferable that the output section  60  outputs the pixel data and the triggering data to a common output signal line Lout, and it is also preferable that the output section  60  outputs these data as serial data. In these cases, the number of wirings for outputting these data can be reduced, which is advantageous from the standpoint of improvement in reliability. 
     The controlling section  70  is to control the operations of the solid-state image pickup device  1  as a whole. For example, the controlling section  70  controls a row selecting operation in the row selecting section  30 , a column selecting operation in the column selecting section  40 , a data holding operation in the voltage holding section  50 , and output operations of pixel data and triggering data in the output section  60 . Further, the triggering data output from the output section  60  is input to the controlling section  70 , and the controlling section  70  outputs a controlling signal of a charge storing operation, which is instructing each of the pixels P m,1  to P m,N  in the imaging region  10  to perform a charge storing operation when an absolute value of the triggering data is greater than a threshold value. Moreover, the controlling section  70  outputs a clock signal CLK synchronized with the output timing of each bit of each of the pixel data and the triggering data by the output section  60 . 
     In addition, a controlling signal of a charge storing operation, which is instructing each of the pixels P m,1  to P m,N  in the imaging region  10  to perform a charge storing operation may be supplied directly from the controlling section  70  to the imaging region  10 , and may instruct it to perform a charge storing operation along with controlling signals (a Reset(m) signal, a Trans(m) signal, and a Hold(m) signal which will be described later) provided to a gate terminal of each transistor included in each pixel P m,n . Or, a controlling signal of a charge storing operation may be supplied from the controlling section  70  to the row selecting section  30 , and the controlling signals provided to a gate terminal of each transistor included in each pixel P m,n  may be generated on the basis of the controlling signal of the charge storing operation. 
       FIG. 2  is a configuration diagram of the output section  60  included in the solid-state image pickup device  1  according to the present embodiment. The output section  60  shown in this drawing has a differential operating circuit  61 , an integrating circuit  62 , an imaging A/D converting circuit  63 , a triggering A/D converting circuit  64 , a switch SW 61 , and a switch SW 62 . 
     With respect to the differential operating circuit  61 , a voltage value indicating a signal component superimposed with a noise component is input from the holding circuit H n , and a voltage value indicating a noise component as well is input from the holding circuit H n , and the differential operating circuit  61  outputs a voltage value according to a difference between the both values. The voltage value output from the differential operating circuit  61  indicates a signal component whose noise component has been removed. With respect to the integrating circuit  62 , electric charge output from the triggering photosensitive region  20  is input to be stored, and the integrating circuit  62  outputs a voltage value according to an amount of the stored electric charge. 
     The voltage value output from the differential operating circuit  61  is input to the imaging A/D converting circuit  63 , and the imaging A/D converting circuit  63  converts the input voltage value from analog to digital, and outputs a digital value (pixel data) which is a result of the A/D conversion. The voltage value output from the integrating circuit  62  is input to the triggering A/D converting circuit  64 , and the triggering A/D converting circuit  64  converts the input voltage value from analog to digital, and outputs a digital value (triggering data) which is a result of the A/D conversion. 
     The imaging A/D converting circuit  63  performs an A/D-converting operation after the period instructed by the controlling signal of the charge storing operation to output: pixel data. During a period when the imaging A/D converting circuit  63  does not output the pixel data, the triggering A/D converting circuit  64  outputs triggering data. The triggering A/D converting circuit  64  operates at a lower speed or with a smaller number of output bits as compared with the imaging A/D converting circuit  63 . 
     The switch SW 61  is controlled by a sel_data signal output from the controlling section  70  to perform an opening/closing operation. When the switch SW 61  is closed, the pixel data output from the imaging A/D converting circuit  63  is output to the output signal line Lout. The switch SW 62  is controlled by a sel_trig signal output from the controlling section  70  to perform an opening/closing operation. When the switch SW 62  is closed, the triggering data output from the triggering A/D converting circuit  64  is output to the output signal line Lout. The switch SW 61  and the switch SW 62  are not simultaneously closed in any case. 
     In addition, the output section  60  may include a common A/D converting circuit serving as the imaging A/D converting circuit  63  and the triggering A/D converting circuit  64 . In that case, the A/D converting circuit operates at a lower speed or with a smaller number of output bits at the time of outputting the triggering data as compared with the time of outputting the pixel data. For example, when the A/D converting circuit is a pipeline system, a number of stages to be operated is made less at the time of outputting the triggering data as compared with the time of outputting the pixel data. Further, for example, when the A/D converting circuit is a successive approximation system using a plurality of capacitors, a number of capacitors to be used is made less at the time of outputting the triggering data as compared with the time of outputting the pixel data. 
       FIG. 3  is a diagram showing the circuit configurations of a pixel P m,n  and a holding circuit H n  included in the solid-state image pickup device  1  according to the present embodiment. In this drawing, the pixel P m,n  is shown as a representative of the M×N pixel P 1,1  to P M,N  and the holding circuit H n  is shown as a representative of the N holding circuits H 1  to H N . 
     The pixel P m,n  is of an APS (Active Pixel Sensor) type, and includes a photodiode PD and five transistors T 1  to T 5 . As shown in this drawing, the transistor T 1 , the transistor T 2 , and the photodiode PD are connected in series in this order, and a reference voltage Vb 1  is input to a drain terminal of the transistor T 1 , and an anode terminal of the photodiode PD is grounded. 
     The transistor T 3  and the transistor T 4  are connected in series, and a reference voltage Vb 2  is input to a drain terminal of the transistor T 3 , and a source terminal of the transistor T 4  is connected to a wiring Vline(n). A junction point between the transistor T 1  and the transistor T 2  is connected to a gate terminal of the transistor T 3  via the transistor T 5 . Further, a constant current source is connected to the wiring Vline(n). 
     A Reset(m) signal is input to a gate terminal of the transistor T 1 , a Trans(m) signal is input to a gate terminal of the transistor T 2 , an Address(m) signal is input to a gate terminal of the transistor T 4 , and a Hold(m) signal is input to a gate terminal of the transistor T 5 . These Reset(m) signal, Trans(m) signal, Address(m) signal, and Hold(m) signal are output from the row selecting section  30  under the control of the controlling section  70  to be input in common to the N pixel P m,1  to P m,N  in the m-th row. 
     When the Reset(m) signal and the Trans(m) signal are at a high level, electric charge is discharged from a junction capacitance section (the charge storing section: the factor is the same as that of the photodiode PD) of the photodiode PD. When the Hold(m) signal is also at a high level, the electric potential of the gate terminal of the transistor T 3  is reset. Thereafter, when the Reset(m) signal, the Trans(m) signal, and the Hold(m) signal cone to a low level, the electric charge generated in the photodiode is stored in the junction capacitance section. When the Hold(m) signal is at a low level and the Address(m) signal is at a high level, a noise component is output from the pixel P m,n  to the wiring Vline(n). Then, when the Trans(m) signal, the Hold(m) signal, and the Address(m) signal come to a high level, a voltage value according to the amount of the electric charge stored in the junction capacitance section of the photodiode PD is output as a signal component to the wiring Vline(n). 
     The holding circuit H n  includes two capacitors C 1  and C 2  and four switches SW 11 , SW 12 , SW 21 , and SW 22 . In this holding circuit H n , the switch SW 11  and the switch SW 12  are connected in series so as to be provided between the wiring Vline(n) and a wiring Hline_s, and one end of the capacitor C 1  is connected to a junction point between the switch SW 11  and the switch SW 12 , and the other end of the capacitor C 1  is grounded. Further, the switch SW 21  and the switch SW 22  are connected in series so as to be provided between the wiring Vline(n) and a wiring Hline_n, and one end of the capacitor C 2  is connected to a junction point between the switch SW 21  and the switch SW 22 , and the other end of the capacitor C 2  is grounded. 
     In this holding circuit H n , the switch SW 11 , is opened and closed according to a level of a set_s signal supplied from the controlling section  70 . The switch SW 21  is opened and closed according to a level of a set_n signal supplied from the controlling section  70 . The set_s signal and the set_n signal are input in common to the N holding circuits H 1  to H N . The switches SW 12  and SW 22  are opened and closed according to a level of an hshift(n) signal supplied from the controlling section  70 . 
     In this holding circuit H n , a noise component that is being output from the pixel P m,n  to the wiring Vline(n) when the set_n signal is switched from a high level to a low level to open the switch SW 21  is held as a voltage value out_n(n) by the capacitor C 2 . A signal component that is being output from the pixel P m,n  to the wiring Vline(n) when the set_s signal is switched from a high level to a low level to open the switch SW 11  is held as a voltage value out_s(n) by the capacitor C 1 . Then, when the hshift(n) signal comes to a high level, the switch SW 2  is closed, and the voltage value out_s(n) that has been held by the capacitor C 1  is output to the wiring Hline_s, and further, the switch SW 22  is closed, and the voltage value out_n(n) that has been held by the capacitor C 2  is output to the wiring Hline_n. A difference between these voltage values out_s(n) and out_n(n) indicates a voltage value according to the amount of electric charge generated by the photodiode PD in the pixel P m,n . 
       FIG. 4  is a diagram showing the circuit configuration of the differential operating circuit  61  included in the solid-state image pickup device  1  according to the present embodiment. As shown in this drawing, the differential operating circuit  61  includes amplifiers A 64  to A 66 , switches SW 64  and SW 65 , and resistors R 1  to R 4 . An inverting input terminal of the amplifier A 66  is connected to an output terminal of the buffer amplifier A 64  via the resistor R 1 , and is connected to its own output terminal via the resistor R 3 . A non-inverting input terminal of the amplifier A 66  is connected to an output terminal of the buffer amplifier A 65  via the resistor R 2 , and is connected to the ground potential via the resistor R 4 . An output terminal of the amplifier A 66  is connected to an input terminal of the imaging A/D converting circuit  63 . An input terminal of the buffer amplifier A is connected to the N holding circuits H 1  to H N  via the wiring Hline_s, and is connected to the ground potential via the switch SW 64 . An input terminal of the buffer amplifier A 65  is connected to the N holding circuits H 1  to H N  via the wiring Hline_n, and is connected to the ground potential via the switch SW 65 . 
     The switches SW 64  and SW 65  of the differential operating circuit  61  are controlled by an hreset signal to perform opening/closing operations. When the switch SW 64  is closed, the voltage value to be input to the input terminal of the buffer amplifier A 64  is reset. When the switch SW 65  is closed, the voltage value to be input to the input terminal of the buffer amplifier A 65  is reset. When the switches SW 64  and SW 65  are open, voltage values out_s(n) and out_n(n) output to the wirings Hline_s and Hline_n from one holding circuit H n  among the N holding circuits H 1  to H N  are input to the input terminals of the buffer amplifiers A 64  and A 65 . Assuming that the buffer amplifiers A 64  and A 65  respectively have an amplification factor of 1 and the respective resistance values of the four resistors R 1  to R 4  are equal to one another, a voltage value output from an output terminal of the differential operating circuit  61  indicates a difference between the voltage values input respectively through the wiring Hline_s and the wiring Hline_n. 
       FIG. 5  is a diagram showing the circuit configuration of the integrating circuit  62  included in the solid-state image pickup device  1  according to the present embodiment. As shown in this drawing, the integrating circuit  62  includes an amplifier A 67 , a capacitor C 67 , and a switch SW 67 . The capacitor C 67  and the switch SW 67  are connected in parallel to one another so as to be provided between an inverting input terminal and an output terminal of the amplifier A 67 . The inverting input terminal of the amplifier A 67  is connected to the triggering photosensitive region  20 . A non-inverting input terminal of the amplifier A 67  is connected to a reference potential Vb. The output terminal of the amplifier A 67  is connected to an input terminal of the triggering A/D converting circuit  64 . The switch SW 67  of the integrating circuit  62  is controlled by a reset_trig signal to perform an opening/closing operation. When the switch SW 67  is closed, electric charge is discharged from the capacitor C 67 , and a voltage value output from the integrating circuit  62  is reset. When the switch SW 67  is open, the electric charge output from the triggering photosensitive region  20  is stored in the capacitor C 67 , and a voltage value according to the amount of stored electric charge is output from the integrating circuit  62 . 
     Next, description will be given of an example of operations of the solid-state image pickup device  1  according to the present embodiment.  FIG. 6  is a timing chart showing an example of operations of the solid-state image pickup device  1  according to the present embodiment. The solid-state image pickup device  1  operates under the control of the controlling section  70 . In this drawing, there are shown (a) Light intensity to be incident into the solid-state image pickup device  1 , (b) Clock signal CLK output from the controlling section  70 , (c) Digital signal Dout (pixel data Ddata(m) or triggering data Dtrig) output from the output section  60  to the output signal line Lout, (d) Controlling signal of the charge storing operation output from the controlling section  70 , (e) Triggering data reading operation by the triggering photosensitive region  20 , the integrating circuit  62 , and the triggering A/D converting circuit  64 , and (f) Pixel data reading operation by the imaging region  10 , the voltage holding section  50 , the differential operating circuit  61 , and the imaging A/D converting circuit  63  in this order. 
     In this drawing, with respect to the m-th row in the imaging region  10 , a digital value (pixel data) output from the imaging A/D converting circuit  63  is expressed as Ddata(m), and a digital value (triggering data) output from the triggering A/D converting circuit  64  is expressed as Dtrig. Clock times t 0 , t 1 , t 2 , t 3 , t t 5 , and t 6  indicate trailing edge clock times of the clock signal CLK output from the controlling section  70 . Further, before the clock time t 0  and after the clock time t 7 , a light is not incident into the solid-state image pickup device  1 , and a light is incident into the solid-state image pickup device  1  during the period from the clock time t 0  to the clock time t 7 . 
     During a given period immediately after a power supply is applied to the solid-state image pickup device  1 , the controlling signal of the charge storing operation, which is output from the controlling section  70  is set to be a high level. Then, after the controlling signal of the charge storing operation is shifted to a low level, pixel data of one frame are output from the output section  60  through the imaging region  10 , the voltage holding section  50 , the differential operating circuit  61 , the imaging A/D converting circuit  63 , and the switch SW 61 . The pixel data output at this time is insignificant. However, because the controlling signal of the charge storing operation is set to be a high level during the given period after application of power, each pixel P m,n  in the imaging region  10  and the other circuits are reset, which allows normal performance thereafter. 
     Thereafter, before the clock time t 0 , the triggering data Dtrig according to the amount of light received at the triggering photosensitive region  20  is output from the output section  60  through the integrating circuit  62 , the triggering A/D converting circuit  64 , and the switch SW 61 . The clock signal CLK output from the controlling section  70  is to be synchronized with the output timing of each bit of the triggering data. Then, in the controlling section  70 , it is judged that an absolute value of the triggering data Dtrig is less than the threshold value, and that a light is not incident into the solid-state image pickup device  1  (or the incident light amount is less than a certain level), and the controlling signal of the charge storing operation is kept to be a low level. 
     Further, before the clock time t 0 , the respective pixels P 1,1  to P M,N  in the imaging region  10  are kept in a reset state. That is, the Reset(m) signal, the Trans(m) signal, and the Hold (m) signal supplied from the row selecting section  30  to each pixel P m,n  are all set to be a high level, and the transistors T 1 , T 2 , and T 5  are in an on-state, and electric charge is discharged from the junction capacitance section (the charge storing section) of the photodiode PD, and the electric potential of the gate terminal of the transistor T 3  is reset. Further, the imaging A/D converting circuit  63  is in a suspended state, and the switch SW 61  is open. 
     When light begins to be incident into the solid-state image pickup device  1  after the clock time t 0 , it is judged in the controlling section  70  that an absolute value of the triggering data Dtrig output from the output section  60  is greater than the threshold value, and that the light is incident into the solid-state image pickup device  1  (or an incident light amount is greater than a certain level), and the controlling signal of the charge storing operation is shifted to a high level. 
     Then, during the period from the trailing edge clock time t 3  of the clock signal CLK after the controlling signal of the charge storing operation is shifted to a high level up to the trailing edge clock time t 6  of the clock signal CLK after the controlling signal of the charge storing operation is shifted to a low level, in each pixel P m,n  in the imaging region  10 , the Reset(m) signal, the Trans(m) signal, and the Hold (m) signal shift to a low level, and the transistors T 1 , T 2 , and T 5  come into an off-state, and the electric charge generated in the photodiode is stored in the junction capacitance section. 
     During this period from the clock time t 3  to the clock time t 6 , triggering data Dtrig according to an amount of the light received at the triggering photosensitive region  20  is output from the output section  60  through the integrating circuit  62 , the triggering A/D converting circuit  64 , and the switch SW 61 . The clock signal CLK output from the controlling section  70  is to be synchronized with the output timing of each bit of the triggering data. Further, the imaging A/D converting circuit  63  is in a suspended state, and the switch SW 61  is open. 
     In addition, a cumulative incident light amount can be monitored on the basis of the triggering data output at this time. Then, a time for charge storage (i.e., a period when the controlling signal of the charge storing operation is at a high level) in the imaging region  10  can be set to an appropriate value on the basis of the monitored cumulative incident light amount. Further, the controlling signal of the charge storing operation may be shifted to a low level at a point in time when the monitored incident light amount is made less than a certain level. Or, in a case in which an incident light amount can be predicted in advance, the controlling signal of the charge storing operation may be set to an appropriate value on the basis of the predicted value. 
     During the period from the clock time t 6  up to the clock time t 7  of the clock signal CLK after the controlling signal of the charge storing operation is shifted to a low level, in each pixel P m,n  in the imaging region  10 , the Reset(m) signal and the Address(m) signal shift to a low level, and the transistors T 1  and T 4  come into an off-state, and the Trans(m) signal and the Hold(m) signal shift to a high level, and the transistors T 2  and T 5  come into an on-state. In accordance therewith, the electric charge stored in the junction capacitance section until that time move through the transistors T 2  and T 5  to the gate terminal of the transistor T 3  to be, held. However, because the transistor T 4  is in an off-state, a voltage value according to the amount of the stored electric charge is not output from each pixel P m,n  to the wiring Vline(n) in any case. 
     During this period from the clock time t 6  up to the clock time t 7 , both of the imaging A/D converting circuit  63  and the triggering A/D converting circuit  64  are in a suspended state, and no pixel data and triggering data is output: from the output section  60 . Further, the clock signal CLK is not output from the controlling section  70 . 
     During the following period from the clock time t 7  to the clock time t 9 , N pixel data Ddata( 1 ) according to the amounts of the stored electric charge in the N pixels P 1,1  to P 1,N  in the first row in the imaging region  10  are output from the output section  60 . In detail, during the period from the clock time t 7  to the clock time t 8 , the Address( 1 ) signal comes to a low level only in the first row in the imaging region  10 , and the transistor T 4  comes into an on-state, and a voltage value according to the amount of stored electric charge in each pixel P 1,n  in the first row is output to the wiring Vline(n) to be held by the holding circuit H n  of the voltage holding section  50 . Then, voltage values sequentially output from the respective holding circuits H n  during the period from the clock time t 8  to the clock time t 9  are input into the imaging A/D converting circuit  63  via the differential operating circuit  61  to be converted from analog to digital, and N pixel data Ddata( 1 ) are sequentially output from the imaging A/D converting circuit  63  via the switch SW 61 . During this period from the clock time t 7  to the clock time t 9 , the clock signal CLK output from the controlling section  70  is to be synchronized with the output timing of each bit of the imaging data. Further, the triggering A/D converting circuit  64  is in a suspended state, and the switch SW 62  is open. 
     During the following period from the clock time t 9  to the clock time t 11 , N pixel data Ddata( 2 ) according to the amounts of the stored electric charge in the N pixels P 2,1  to P 2,N  in the second row in the imaging region  10  are output from the output section  60 . In detail, during the period from the clock time t 9  to the clock time t 10 , the Address( 2 ) signal comes to a low level only in the second row in the imaging region  10 , and the transistor T 4  comes into an on-state, and a voltage value according to the amount of stored electric charge in each pixel P 2,n  in the second row is output to the wiring Vline(n) to be held by the holding circuit H n  of the voltage holding section  50 . Then, voltage values sequentially output from the respective holding circuits H n  during the period from the clock time t 10  up to the clock time t 11  are input into the imaging A/D converting circuit  63  via the differential operating circuit  61  to be converted from analog to digital, and N pixel data Ddata( 2 ) are sequentially output from the imaging A/D converting circuit  63  via the switch SW 61 . During this period from the clock time t 9  to the clock time t 11 , the clock signal CLK output from the controlling section  70  is to be synchronized with the output timing of each bit of the imaging data. Further, the triggering A/D converting circuit  64  is in a suspended state, and the switch SW 62  is open. 
     In the same way thereafter, N pixel data Ddata(m) according to the amounts of the stored electric charge in the N pixels P m,1  to P m,N  in the m-th row are output from the output section  60  sequentially from the third row to the M-th row in the imaging region  10 . In this way, the pixel data Ddata( 1 ) to Ddata(M) of one frame are output from the output section  60  through the imaging region  10 , the voltage holding section  50 , the differential operating circuit  61 , the imaging A/D converting circuit  63 , and the switch SW 61 . Then, after the pixel data of one frame are output, the device returns to a state which is the same as that before the clock time t 0 . 
     In this way, in the solid-state image pickup device  1  according to the present invention, the imaging A/D converting circuit  63  and the triggering A/D converting circuit  64  are provided, and the two A/D converting circuits  63  and  64  do not simultaneously operate in any case. During the period when it is monitored whether or not a light is incident into the solid-state image pickup device  1 , and during the period when the electric charge generated in the photodiode in each pixel P m,n  in the imaging region  10  is stored in the junction capacitance section after sensing the light incidence, the imaging A/D converting circuit  63  is suspended, and the triggering A/D converting circuit  64  operates. During the period when pixel data is read out after storing the electric charge in each pixel P m,n  in the imaging region  10 , the triggering A/D converting circuit  64  is suspended, and the imaging A/D converting circuit  63  operates. 
     Because the imaging A/D converting circuit  63  for reading out pixel data is required to operate at a high speed, and required to have a given number or more of output bits, the electric power consumption thereof is high. The clock signal CLK output from the controlling section  70  when the imaging A/D converting circuit  63  operates is to be a high-frequency signal in synchronization with the output timing of each bit in the pixel data. For example, in this case, the frequency of the clock signal is 80 MHz, the pixel data is 14-bit data, and the electric power consumption is 500 mW. 
     In contrast thereto, because the triggering A/D converting circuit  64  for reading out triggering data may operate at a low speed, and flier may have a small number of output bits, the electric power consumption thereof is low. The clock signal CLK output from the controlling section  70  when the triggering A/D converting circuit  64  operates is a low-frequency signal in synchronization with the output timing of each bit in the triggering data. For example, in this case, the frequency of the clock signal is 1 MHz, the triggering data is 8-bit data, and the electric power consumption is 25 mW. 
     The solid-state image pickup device  1  according to the present embodiment can achieve the advantageous effects in the following application, for example. that is, provided that scintillators are provided on the respective acceptance surfaces of the imaging region  10  and the triggering photosensitive region  20 , the solid-state image pickup device  1  is capable of converting an incident X-ray beam into a visible light to receive the visible light with the photodiodes in the imaging region  10  or the triggering photosensitive region  20 , and imaging the incident X-ray beam thereby. The solid-state image pickup device  1  in which such scintillators are provided is used for X-ray imaging in an oral cavity. 
     When the solid-state image pickup device  1  is used for X-ray imaging in an oral cavity, a period when an X-ray beam to be imaged is incident is extremely short, and the solid-state image pickup device  1  is required to capture the timing of X-ray incidence to image the X-ray beam. Then, the solid-state image pickup device  1  reads out triggering data by the triggering photosensitive region  20 , the integrating circuit  62 , and the triggering A/D converting circuit  64  before X-ray incidence, and senses the X-ray incidence on the basis of the triggering data. Then, after the solid-state image pickup device  1  senses the X-ray incidence, the solid-state image pickup device  1  reads out pixel data by the imaging region  10 , the voltage holding section  50 , the differential operating circuit  61 , and the imaging A/D converting circuit  63 . In this way, the solid-state image pickup device  1  is capable of capturing the timing of X-ray incidence to image the X-ray beam. 
     In this way, in a case m which the solid-state image pickup device  1  is used for X-ray imaging in an oral cavity, the triggering A/D converting circuit  64  can be suspended before X-ray incidence, and the triggering A/D converting circuit  64  may be operated only at the time of X-ray incidence. Accordingly, the solid-state image pickup device  1  is capable of suppressing increase in electric power consumption even if an attempt is made to increase the number of pixels or speed up imaging. 
     Further, in a case in which the solid-state image pickup device  1  is used for X-ray imaging in an oral cavity, it is preferable that pixel data and triggering data are output to the common output signal line Lout, and further, these data are output as serial data. In these cases, it is possible to reduce the number of wirings for outputting these data, which results in improvement in reliability. 
     Further, the solid-state image pickup device  1  is capable of storing electric charge generated in the photodiode during, the same period in each of the M×N pixels P 1,1  to P M,N  in the imaging region  10  by the charge storing section after sensing light incidence, and after the charge storage, pixel data on each pixel P m,n  can be sequentially output from the output section  60 . Accordingly, even when a temporal change in an incident light amount is rapid, it is possible to obtain the incident light amounts of all the pixels during the same period, which makes it possible to perform highly precise imaging. 
     The present invention is not limited to the above-described embodiment, and various modifications are possible. For example, in the above-described embodiment, the controlling section  70  generates a controlling signal of a charge storing operation. However, an external device that generates a controlling signal of a charge storing operation on the basis of triggering data may be provided separately from the solid-state image pickup device. In this case, triggering data is output to the external device from the output section of the solid-state image pickup device, and a controlling signal of a charge storing operation is generated by the external device on the basis of the output triggering data, and the generated controlling signal of the charge storing operation is provided to the solid-state image pickup device from the external device. 
     In this way, at the time of sensing light incidence based on a comparison of values between the triggering data and a threshold value, the threshold value can be flexibly adjusted by the external device. Further, a period when the controlling signal of the charge storing operation makes an instruction to store electric charge (i.e., a period when electric charge generated in the photodiode in each pixel is stored by the charge storing section) can be flexibly adjusted by the external device, which makes it possible to easily respond to a wide range of incident light amounts. 
     The above-described solid-state image pickup device includes the triggering photosensitive region  20 , the imaging region  10  having a plurality of pixels, in which electric charge generated in the pixel P(m,n) during a first period (t 3  to t 6 ) is stored, and the output section  60  that outputs triggering data (trig) which is a digital value from the triggering photosensitive region  20 , and outputs pixel data (Ddata) which is a digital value from the imaging region  10  during a second period (t 8  to t 9 ) different from the first period (t 3  to t 6 ), and operates with lower power consumption at the time of outputting the triggering data (Dtrig) as compared with the time of outputting the pixel data (Ddata). Accordingly, the power consumption of the entire device can be reduced. 
     Further, the output section  60  outputs the triggering data (Dtrig) from the triggering photosensitive region  20  during a period overlapping with the first period (t 3  to t 6 ). In this example, because the triggering data is output during a period overlapping with the first period when storage is achieved, an entire period from charge storage to data output can be shortened.