Abstract:
In a control circuit for controlling a solid-state image pickup device, two sorts of image data are read out separately with differing sensitivities. A timing generator control in a digital camera controls a timing signal generator to the interlace scanning or to all-pixel scanning, and outputs a timing signal, consistent with this control, to the driver. The driver outputs a driving signal, consistent with the timing signal, to the solid-state image pickup device included in an image pickup unit to read out signal charges. In particular, in interlace scanning, readout of signal charges of main pixels of the image pickup device is separated from that of subsidiary pixels of the device.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a control circuit for controlling a solid-state image pickup device, and to a method for driving an image pickup device. The control circuit for controlling a solid-state image pickup device according to the present invention specifically pertains to the technique of controlling the generation of timing signals for reading out, e.g. image data with a wide dynamic range. The method for driving an image pickup device according to the present invention pertains especially to a procedure of reading out signal charges from a solid-state image pickup device which provides for a wide dynamic range.  
         [0003]     2. Description of the Background Art  
         [0004]     U.S. Patent Application Publication 2003/0141564 A1 to Ryuji Kondo, et al., teaches a solid-state image pick up device in which two pixels, or photosensitive cells, of different photo-sensitivities are employed for each pixel in order to provide for a wide dynamic range. Each pixel is divided into two photosensitive areas, one formed to a higher sensitivity and the other formed to a lower sensitivity, in order to output pixel data of higher and lower sensitivities free of spatial deviation or deviation along time axis. Two images with different sensitivities may be obtained simultaneously by outputting these two sorts of pixel data as one pixel.  
         [0005]     If a plural number of color filter segments, arranged on opposite sides of a vertical transfer path, are taken into consideration, color filter segments are arranged in a column of green segments G and a column of blue segments B and red segments R on one side of the vertical transfer path, and a column of green segments G and a column of red segments R and blue segments B on the other side of the vertical transfer path. The pixels are read with the set of the column of green segments G and the column of blue segments B and red segments R in one field and with the set of the column of green segments G and the column of red segments R and blue segments B in the other field.  
         [0006]     Meanwhile, interlace readout of signal charges from such an image pickup device does not cause the pixel data of high and low sensitivities to be output separately from each other. Thus, for readout, a line memory is needed for temporarily storing the two sorts of the pixel data, and hence the use of such a solid-state image pickup device leads to increased costs.  
       SUMMARY OF THE INVENTION  
       [0007]     It is an object of the present invention to provide a control circuit for controlling a solid-state image pickup device for separately reading out the two sorts of pixel data of different sensitivities, and a method for driving the solid-state image pickup device.  
         [0008]     In accordance with the present invention, there is provided a control circuit for controlling a solid-state image pickup device, made up of first photosensitive cells of relatively higher sensitivity to incident light from an imaging field captured and second photosensitive cells of relatively lower sensitivity than the higher sensitivity to the incident light. The first and second photosensitive cells are arranged in a two-dimensional array for photo-electrically transducing the incident light. The control circuit controls the readout of the signal charges stored in the solid-state image pickup device. The control circuit controls a timing signal generator which generates a timing signal for interlace scanning or for all-pixel scanning in reading out the signal charges in the first and second photosensitive cells. The control circuit transmits the timing signal generated from the timing signal generator by the control circuit to a driving signal generator adapted for generating a driving signal. The control circuit outputs the driving signal, generated by the driving signal generator, to the solid-state image pickup device for reading out the signal charges stored in the first and second photosensitive cells, responsive to the driving signal. The control circuit in the interlace scanning controls the readout of the signal charge in a plurality of number of times from the solid-state image pickup device.  
         [0009]     The control circuit for solid-state image pick up device according to the present invention controls the timing signal generator to interlace scanning or to all-pixel scanning, and outputs a timing signal consistent with the control to driving signal generator. The driving signal generator outputs a driving signal, consistent with the driving signal, to the solid-state image pickup device, to read out signal charges. In particular, in interlace scanning, the signal charges from the main pixels of the solid-state image pickup device can be read out separately from those from the subsidiary pixels of the device.  
         [0010]     In accordance with the present invention, there is also provided a method of driving a solid-state image pickup device, made up of first photosensitive cells of relatively higher sensitivity to incident light from an imaging field captured and second photosensitive cells of relatively lower sensitivity than the higher sensitivity to the incident light. The first and second photosensitive cells are arranged in a two-dimensional array for photo-electrically transducing the incident light. The method includes the steps of controlling the readout of signal charges in the first and second photosensitive cells to interlace scanning or all-pixel scanning, and controlling the readout of signal charges in a plurality of number of times in the interlace scanning.  
         [0011]     The method of driving a solid-state image pick up device, according to the present invention, controls the readout of signal charges in the first and second photosensitive cells to the interlace scanning or to all-pixel scanning. In particular, in the interlace scanning, the signal charges from the first photosensitive cells can be read out separately from those from the second devices. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     The objects and features of the present invention will become more apparent from consideration of the following detailed description taken in conjunction with the accompanying drawings in which:  
         [0013]      FIG. 1  is a schematic block diagram showing an embodiment of a digital camera to which is applied a control circuit for controlling a solid-state image pickup device according to the present invention;  
         [0014]      FIG. 2  is a plan view partially showing the essential portion of the photosensitive array of the solid-state image pickup device and a vertical transfer path arranged in an image pickup unit of  FIG. 1 ;  
         [0015]      FIGS. 3A through 3D  are schematic cross-sectional views showing the cross sections of the main and subsidiary pixels in the photosensitive array of  FIG. 2 ;  
         [0016]      FIGS. 4A and 4B  are timing charts for illustrating signal charge readout in the digital camera of  FIG. 1  from one main pixel field to another;  
         [0017]      FIGS. 5A and 5B  are timing charts for illustrating signal charge readout in the digital camera of  FIG. 1  from one subsidiary pixel field to another;  
         [0018]      FIG. 6  is a timing chart for illustrating vertical signal charge transfer in the digital camera of  FIG. 1 ;  
         [0019]      FIG. 7  is a timing chart useful for understanding the saturation suppression voltage of a subsidiary pixel field in the digital camera of  FIG. 1 ; and  
         [0020]      FIG. 8  is a timing chart useful for understanding the different saturation suppression voltages of the main and subsidiary pixel fields in the digital camera of  FIG. 1 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0021]     With reference to the accompanying drawings, a preferred embodiment of a control circuit for controlling a solid-state image pickup device according to the present invention will be described in detail. The present embodiment is adapted for a case where the control circuit for controlling a solid-state image pickup device according to the present invention is applied to a digital camera  10 . Components not directly relevant to understanding the present invention are not shown in the drawings, and a description associated therewith will be dispensed with.  
         [0022]     Referring to  FIG. 1 , the digital camera  10  of the present embodiment includes an optical system  12 , an image pickup unit  14 , a pre-processor  16 , a signal processor  18 , an operating pane  120 , a system controller  22 , a timing generator (TG) control  24 , a timing signal generator  26 , a driver  28 , a medium interface (I/F)  30 , a recording medium  32  and a display monitor  34 , which are interconnected as illustrated.  
         [0023]     The optical system  12  has the function of receiving incident light  13  from an object field to form an optical image on the image pickup unit  14 . The optical system  12  is responsive to a zooming operation or a half-stroke operation of a shutter release key, not shown, applied to the operating panel  20 , to adjust its angle of field or focal length.  
         [0024]     In the image pickup unit  14 , there are arrayed color filter segments so that the color filter segments are in register with the photosensitive cells in the incoming direction of the incident light  13 . The image pickup unit  14  includes an image pickup device or image sensor  36  having the function of color-separating the incident light  13  and converting the light of the color components, resulting from color separation, into signal charges, by the photosensitive cells, to output a corresponding electrical signal. Referring additionally to  FIG. 2 , showing the image pickup device  36 , the color filter segments of three prime colors, namely red (R), green (G) and blue (B), are arrayed so that the pixels of two neighboring rows are shifted by a one-half pixel pitch with respect to the pixel pitch PP in the horizontal direction. There are two types of the pixels of the image pickup device  36 , one is relatively higher sensitivity pixels  38  and the other is relatively lower sensitivity pixels  40 .  
         [0025]     The image pickup device  36  of the instant embodiment has two kinds of micro-lenses  42  and  44  in the form of on-chip lens. In order to provide for a difference in the light condensing power for the incident light  13  and hence to provide for a difference in the optical sensitivity, the micro-lenses  42  and  44  are different in size or spherical curvature as shown in  FIGS. 3A through 3D . The relatively higher and lower sensitivity pixels  38  and  40  are briefly shown in cross-sectional views taken along dot-and-dash lines  3 B- 3 B and  3 D- 3 D of  FIGS. 3A and 3C , respectively. The higher and lower sensitivity pixels  38  and  40  constitute a photosensitive layer  48  in a substrate  46  for photo-electrically converting the incident light  13 . A transparent member  50  is provided for covering the upper surface of the photosensitive layer  48 . A pair of electrodes  52 ,  52  are formed on either sides of and on the upper surface of the photosensitive layer  48 . The electrodes  52 ,  52  are covered up by an optical shielding member  54  adapted for shielding the incident light  13 . The light shielding member  54  has its upper surface smoothed in its entirety with a transparent member  50 . On the smoothed upper surface, there are formed color filter segments  56  exhibiting spectral sensitivity characteristics. On the top of the color filter segments  56 , there are arrayed micro-lenses  42  and  44  having differential curvatures, as apparent from  FIGS. 3B and 3D .  
         [0026]     Directly below the electrodes  52 , there are arrayed vertical transfer paths, not shown, depending on the levels of the driving signals transmitted to the electrodes.  
         [0027]     For the higher sensitivity pixel, such a micro-lens having a larger lens diameter and hence a higher light condensing power may desirably be formed on the light incident side. For the lower sensitivity pixel, such a micro-lens having a lens diameter smaller than the normal or larger lens diameter is used.  
         [0028]     Reverting now to  FIG. 2 , the higher and lower sensitivity pixels are arranged every other row and every other column. The higher and lower sensitivity pixels are also termed the main and subsidiary pixels, respectively. As the color filter segments, higher and lower sensitivity pixels are arranged as a set or pair so that two pixels of the same color are arrayed for extending in an obliquely upward direction on the photosensitive array  36 . By this array of the color filter segments, two consecutive ones of every four rows are for the colors G and B for with the alternating two rows neighboring thereto, or remaining rows, are for the colors R and B.  
         [0029]     In the image pickup device  36 , a field shift gate  60  is formed between the relatively higher and lower sensitivity pixels  38  and  40  and the vertical transfer path  58 . The field shift gate  60  is meanderingly formed because the higher and lower sensitivity pixels  38  and  40  are arrayed with a shift of one half of the pixel pitch, equal to PP/2.  
         [0030]     The signal charges are read out from the image pickup device  36  with a row of the main pixels and a row of the subsidiary pixels, totaling at two rows, as a first field depicted with reference numerals  110  and  112 , respectively, in  FIG. 2 , and with a row of the main pixels and a row of the subsidiary pixels, totaling at two rows, and neighboring to the first-stated two rows of the main and subsidiary pixels, as a second field depicted with reference numerals  114  and  116 , respectively. In the present embodiment, distinction is made in the signal readout of the first field. More specifically, the vertical driving signals are supplied to the main pixels from electrodes V 3 A and V 3 B, while being supplied to the subsidiary pixels from electrodes V 1 A and V 1 B. By forming the electrodes in this manner, vertical thinning becomes possible in signal readout from the image pick up device  36  in response to the vertical driving signal transmitted to only one electrode of each of the main and subsidiary pixels. For all-pixel readout, the same vertical driving signals ΦV 1  and ΦV 3  are supplied, in the image pickup device  36 , without making any distinctions. In the following, signals are designated with reference numerals of connections on which they appear. The signal readout from the image pickup device  36  will be described subsequently. The system for reading out signals from the image pickup device  36  may not be restricted to the two-field reading but may be such that the image pickup device may be read out on an n-field basis, where n is a natural number more than unity, or alternatively read out in a thinning-out fashion. The image pickup unit  14  outputs an analog image signal  62 , as read out from the image pickup device  36 , to the pre-processor  16 .  
         [0031]     The pre-processor  16  has the function of performing noise reduction and digitization on the analog image signal  62  as supplied. The correlated double sampling (CDS) circuit, not shown, reduces the noise contained in the analog image signal  62  to transmit the resulting noise-free analog image signal to an analog-to-digital (AD) converter, also not shown. The AD converter digitizes the noise-free analog image signal. The pre-processor  16  outputs digitized image data  64  over a bus  66  and a signal line  68 .  
         [0032]     The signal processor  18  has the function of performing the processing for providing for synchronizing, luminance and chrominance (Y/C) signal conversion, compression/decompression and display conversion, for the digitized image data  64  supplied thereto in the recording compression mode. The processing for providing for synchronizing means the processing for providing for the same output timing of the three prime colors for each pixel. The signal processor  18  outputs the digitized image data  64 , supplied thereto in the recording raw mode, without performing any signal processing. When a through picture mode is selected, i.e. an image captured by the image pickup device  14  is directly to be displayed on the display monitor  34 , the signal processor  18  performs the processing for providing for the synchronizing, Y/C signal conversion and display conversion on the digitized image data  64  to output display image data  70  on the monitor  34 .  
         [0033]     In the recording compression mode or in the recording raw mode, the signal processor  18  outputs processed image data to the medium interface  30  over a signal line  68 , a bus  66  and a signal line  72 . The medium interface  30  outputs image data  74  to the recording medium  32 . In image reproduction, the image data  74  is read out from the medium  32  and the so read out data is output to the medium interface  30 . The medium interface  30  outputs the image data  74 , supplied thereto, to the signal processor  18  over the signal line  72 , bus  66  and signal line  68 . The signal processor  18  performs conversion, consistent with the recording mode, on the image data  74 , and transmits the resultant display image data  70  to the monitor  34 .  
         [0034]     The operating panel  20  has the function of manually giving commands on the operations in the digital camera  10 . The operating panel  20  outputs an operating signal  76 , in response to the depressing operation of keys and a shutter button, not shown, in its half or full stroke, and according to the recording modes, to the system controller  22 .  
         [0035]     The system controller  22  has the function of generating control signals for controlling the signal processor  18 , timing generator control  24  and the medium interface circuit  30 . The system controller  22  generates control signals  78  and  80  in response to the operating signal  76 . The system controller  22  generates the control signal  78  for controlling the timing generator control  24 , to output the so generated control signal to the timing generator control  24 . The system controller  22  generates the control signal  80  for controlling the signal processor  18  and the medium interface  30 , and outputs the so generated control signal  80 .  
         [0036]     The timing generator control  24  has the function of controlling the timing signal generator  26  for generating the signal in depending on whether or not the signals are to be read by a thinning readout. The timing generator control  24  also has the function of modifying a driving signal from the driver  28  responsively to readout from the subsidiary pixel field. The timing generator control  24  generates a control signal  82  for signal generation in the timing signal generator  26 . The control signal  82  exercises control for reading out main and subsidiary pixels in respective different fields, reading out only main pixels in respective different fields, simultaneously reading out all of the main and subsidiary pixels in distinct fields, or for reading out the pixels by thinning readout. The control signal  82  is generated responsive to control by the control signal  78 , while the control signal  78  gives a command which readout is to be used responsive to the operating signal  76 .  
         [0037]     The timing generator control  24  generates and outputs a driving signal, in particular a control signal  84  which modifies or modulates the substrate potential in reading out the subsidiary pixels. This operation is not limited to readout of the subsidiary pixels but can also be carried out in reading out the main pixels. It is desirable to provide for differences in the modification of the substrate potential.  
         [0038]     The timing signal generator  26  has the function of generating a timing signal conforming to all-pixel readout and to thinned readout. The timing signal generator  26  generates, e.g. a vertical synchronous signal VD, a horizontal synchronous signal HD, an overflow drain (OFD) signal, a vertical timing signal and a horizontal timing signal to output the so generated signals to the driver  28  as a timing signal  86 .  
         [0039]     The driver  28  has the function of generating a driving signal consistent with the timing signal  86 . In particular, the driver  28  outputs vertical driving signals ΦV 1 A, ΦV 1 B, ΦV 2 , ΦV 3 A, ΦV 3 B, ΦV 4 , ΦV 5 , ΦV 6 , ΦV 7  and ΦV 8  and an OFD signal, as a driving signal  88 , to the image pickup device  36 . The OFD signal is a combination of the substrate potential, modified in reading out the subsidiary pixels, and the sweep-out signal or the draining signal.  
         [0040]     In the image pickup device  36  of the present embodiment, signal charges read out from the photosensitive cells are transferred vertically in eight-phase driving. The capacity of a packet of the signal charges in such eight-phase driving is smaller than that in, e.g. four-phase driving. Hence, the signal charges, stored in reading out the signal charges, may not be accommodated in a packet for signal charges, so that there may occur the overflow of the signal charges. In order to avoid this from occurring, a packet of signal charges may be formed in an area located above the vertical transfer path neighboring to the field shift gate, thereby increasing the packet capacity. The driving signals V 2 A, V 2 B, V 8 A and V 8 B are designed, e.g. as to values, to cope with the generation of such packets of image signals and the driving signals thus designed, in signal values for example, are applied to generate packets of image signals.  
         [0041]     The medium interface  30  is adapted to interface with the medium  32  responsively to the control signal transmitted from the system controller  22 . The recording medium  32  has the function of recording or reading out data transmitted thereto or recorded therein. The medium  32  is preferably a semiconductor memory. The display monitor  34  is desirably a liquid crystal display.  
         [0042]     The operation of the digital camera  10  will now be described according to the present invention.  FIGS. 4A and 4B  show vertical driving signals transmitted when reading out the first and second fields of the main pixels, respectively. In the first field of the main pixels, shown in  FIG. 4A , the vertical driving signals ΦV 3 A and ΦV 3 B, supplied to the field shift gate  60  of main pixels, shown in  FIG. 2 , are set to the high level “VH” thereof. Moreover, the vertical driving signals ΦV 2 A and ΦV 2 B are also set to the high level “VH” thereof, while the vertical driving signals ΦVLA and ΦVLB are set to the middle level “VM” thereof in order to cope with shortage of the packet capacity. This forms two packets of the deepest potential and a packet of a medium depth of potential in reading out the signal charges of the first field.  
         [0043]     The timing chart of  FIG. 4B  is for the second field of the main pixels. The vertical driving signal ΦV 7 , supplied to the field shift gate  60  for the main pixels, shown in  FIG. 2 , is set to its high level “VH”. In this case, the vertical driving signal ΦV 6  is set to its high level “VH”, and the vertical driving signal ΦV 5  is again set to its middle level “VM”, in order to cope with the shortage of the packet capacity. This forms two packets of the deepest potential and a packet of a medium depth of potential in reading out the signal charges of the second field.  
         [0044]      FIG. 5  shows vertical driving signals transmitted when reading out the first and second fields of the subsidiary pixels. In the first field of the subsidiary pixels, shown in  FIG. 5A , the vertical driving signals ΦV 1 A and ΦVLB, supplied to the field shift gate  60  of main pixels shown in  FIG. 2 , are set to the high level “VH” thereof. Moreover, the vertical driving signals  101  V 8 A and ΦV 8 B are again set to the high level “VH” thereof, while the vertical driving signal ΦV 7  is also set to its middle level “VM”, in order to cope with shortage of the packet capacity. This forms two packets of the deepest potential and a packet of a medium depth of potential in reading out the signal charges of the first field.  
         [0045]     The timing chart of  FIG. 5B  is for the second field of the subsidiary pixels. The vertical driving signal ΦV 5 , supplied to the field shift gate  60  for the main pixels, shown in  FIG. 2 , is set to its high level “VH”. In this case, the vertical driving signal ΦV 4  is set to its high level “VH”, and the vertical driving signals ΦV 3 A and ΦV 3 B are also set to the middle level “VM” thereof, in order to cope with the shortage of the packet capacity. This forms two packets of the deepest potential and a packet of a medium depth of potential in reading out the signal charges of the second field.  
         [0046]     The signal charges, thus read out, are transferred to the horizontal transfer path, not shown, subject to supplying the vertical driving signals shown in  FIG. 6 . This transfer is performed by packet movement brought about responsive to level changes of levels “VL” and “VM”. In the time domain, as the vertical driving signals ΦV 8 A and ΦV 8 B are changed to the level “VM” at time T 1 , a packet is formed in the relevant vertical transfer path  58 . After this packet has been formed, the vertical driving signals ΦV 1 A and ΦVLB are changed at time T 2  to the level “VM”. By these level changes, a packet is formed in the vertical transfer path  58 , beginning from the position where the vertical driving signals ΦV 3 A and ΦV 3 B are supplied, until a time point T 3  when the vertical driving signals. ΦV 8 A and ΦV 8 B are of the low level “VL”. With the vertical driving signals ΦV 8 A and ΦV 8 B being of the low level “VL” at time T 3 , a potential barrier is formed to store six packets of signal charges. At time T 3 , five packets of signal charges are formed from the vertical driving signals ΦV 1 A, ΦV 1 B up to the vertical driving signal ΦV 5 , with the potential barrier operating as a stopper. The signal charges, thus read out in the form of packets of signal charges, are sequentially transferred towards the horizontal transfer path.  
         [0047]     A sequence of operations in the digital camera  10  will now be described. When the shutter release button, now shown, of the operating panel  20  of the digital camera  10  is thrust to its full stroke, an operating signal  76  (S 2 ) is transmitted to the system controller  22 . The system controller  22  in turn outputs the control signal  78  to the timing generator control  24 . The timing generator control  24  transmits the control signal  82  to the timing signal generator  26 . The timing signal generator  26  outputs the timing signal  86 , including the vertical and horizontal synchronous signals VD and HD, shown in  FIG. 7 , lines (a) and (b), and the OFD signal. The OFD shown in  FIG. 7 , line (c), is output from the driver  28  as an electronic shutter signal. The time period during which no electronic shutter signal is output is equivalent to an exposure time  90 . Turning to an output of  FIG. 7 , line (d), there is provided a high-speed drain period  92  until the end of the exposure. The purpose of providing the high-speed drain period  92  is to sweep out signal charges stored in the vertical transfer path  58  and in the horizontal transfer path, not shown.  
         [0048]     After the exposure, the signal charges of the main pixels of the first field are read out by signal charge readout shown in  FIG. 4A . The signal charges are transferred by the transfer driving of  FIG. 6 , without color mixing, by way of performing signal charge readout  94  of the main pixels of the first field. The high-speed draining  92  is again carried out and the signal charges of the main pixels of the second field are then read out by signal charge readout shown in  FIG. 4B , by way of performing signal charge readout  96  of the main pixels of the second field.  
         [0049]     Then, before reading out the subsidiary pixel field, the timing generator control  24  outputs the control signal  84  to the driver  28 . The driver  28  raises or modifies the OFD voltage as from the time of the high-speed draining until the end of the readout of the signal charges of the fields of the subsidiary pixels. This sweeps out signal charges left over in each transfer path. The saturation output of the subsidiary pixels may be suppressed by providing a period of voltage elevation  98  for the OFD voltage. No blooming is produced even if concurrent readout of the totality of pixels (subsidiary pixel fields  100 ) is carried out without making distinction between the first and second fields of the subsidiary pixels. In this manner, the signal charges may be read out from the main and subsidiary pixels in different fields.  
         [0050]     The OFD voltage may be increased not only during the period  98  including the readout period for the subsidiary pixel fields, but also during a period  102  including main pixel fields, as shown in  FIG. 8 , line (c). Turning to the outputting of  FIG. 8 , line (d), signal charges of the main pixels are read out simply to form a main pixel field, without making distinctions of the first and second fields. It is noted that an OFD voltage  108  during the period  98  is set so as to be higher than the OFD voltage  106  during the period  102 .  
         [0051]     Meanwhile, the value of the OFD voltage to be raised is usually determined depending on device characteristics. In distinction from the usual OFD voltage, the OFD voltage in the present embodiment is desirably set stepwise as different saturation suppression voltages for the main and subsidiary pixels.  
         [0052]     The present invention is not limited to the illustrative embodiment applied to a digital camera, but may, of course, be applied to a mobile phone with camera function as well.  
         [0053]     The entire disclosure of Japanese patent application No. 2005-300081 filed on Oct. 14, 2005, including the specification, claims, accompanying drawings and abstract of the disclosure is incorporated herein by reference in its entirety.  
         [0054]     While the present invention has been described with reference to the particular illustrative embodiment, it is not to be restricted by the embodiment. It is to be appreciated that those skilled in the art can change or modify the embodiment without departing from the scope and spirit of the present invention.