Abstract:
A method and apparatus for reducing space and pixel circuit complexity by using a 4-way shared vertically aligned pixels in a same column. The at least four pixels in the pixel circuit share a reset transistor and a source follower transistor, can have a plurality of same colored pixels and a plurality of colors, but do not include a row select transistor.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Embodiments described herein relate generally to improved semiconductor imaging devices and in particular to imaging devices having an array of pixels and to methods of operating the pixels to reduce temporal noise. 
     2. Background of the Invention 
     A conventional four transistor (4T) circuit for a pixel  150  in a pixel array  230  of a CMOS imager is illustrated in  FIG. 1 . The 4T pixel  150  has a photosensor such as a photodiode  162 , a reset transistor  184 , a transfer transistor  190 , a source follower transistor  186 , and a row select transistor  188 . It should be understood that  FIG. 1  shows the circuitry for operation of a single pixel  150 , and that in practical use, there will be an M×N array of pixels arranged in rows and columns with the pixels of the array  230  being accessed using row and column select circuitry, as described in more detail below. 
     The photodiode  162  converts incident photons to electrons, which are selectively passed to a floating diffusion region A through the transfer transistor  190  when activated by a TX 1  control signal. The source follower transistor  186  has its gate connected to floating diffusion region A and thus amplifies the signal appearing at the floating diffusion region A. When a particular row containing pixel  150  is selected by an activated row select transistor  188 , the signal amplified by the source follower transistor  186  is passed on a column line  170  to column readout circuitry ( 242 ,  FIGS. 2-4 ). The photodiode  162  accumulates a photo-generated charge in a doped region of its substrate during a charge integration period. It should be understood that the pixel  150  may include a photogate or other photon to charge converting device, in lieu of a photodiode, as the initial accumulator for photo-generated charge. 
     The gate of transfer transistor  190  is coupled to a transfer control signal line  191  for receiving the TX 1  control signal, thereby serving to control the coupling of the photodiode  162  to region A. A voltage source Vpix is selectively coupled through reset transistor  184  and conductive line  163  to floating diffusion region A. The gate of the reset transistor  184  is coupled to a reset control line  183  for receiving a RST control signal to control the reset operation in which the voltage source Vpix is connected to floating diffusion region A. 
     A row select signal (Row Sel) on a row select control line  160  is used to activate the row select transistor  188 . Although not shown, the row select control line  160 , reset control line  183 , and transfer signal control line  191  are coupled to all of the pixels of the same row of the array. The voltage source Vpix is coupled to transistors  184  and  186  by conductive line  195 . The column line  170  is coupled to the output of all of the pixels of the same column of the array and typically has a current sink  176  at one end. Signals from the pixel  150  are selectively coupled to a column readout circuit  242  ( FIGS. 2-4 ) through the column line  170 . 
     As is known in the art, a value can be read from pixel  150  in a two step correlated double sampling process. First, floating diffusion region A is reset by activating the reset transistor  184 . The reset signal (e.g., Vrst) found at floating diffusion region A is readout to column line  170  via the source follower transistor  186  and the activated row select transistor  188 . During a charge integration period, photodiode  162  produces charge from incident light. This is also known as the image intergration period. After the integration period, the transfer transistor  190  is activated and the charge from the photodiode  162  is passed through the transfer transistor  190  to floating diffusion region A, where the charge is amplified by the source follower transistor  186  and passed to the column line  170  (through the row select transistor  188 ) as an integrated charge signal Vsig. In some instances, the reset signal Vrst is provided after the integrated charge signal Vsig. As a result, two different voltage signals—the reset signal Vrst and the integrated charge signal Vsig—are readout from the pixel  150  onto the column line  170  and to column readout circuitry  242 , where each signal is sampled and held for further processing as is known in the art. Typically, all pixels in a row are readout simultaneously onto respective column lines  170  and the column lines may be activated in sequence or in parallel for pixel reset and signal voltage readout. 
       FIG. 2  shows an example CMOS imager device  201  that includes the pixel array  230  and a timing and control circuit  232 , which provides timing and control signals to enable reading out of signals stored in the pixels in a manner commonly known to those skilled in the art. Example arrays have dimensions of M×N pixels, with the size of the array  230  depending on a particular application. In the illustrated imager device  201 , the pixel signals from the array  230  are readout a row at a time using a column parallel readout architecture. The controller  232  selects a particular row of pixels in the array  230  by controlling the operation of row addressing circuit  234  and row drivers  240 . Reset Vrst and image Vsig signals in the selected row of pixels are provided on the column lines  170  to a column readout circuit  242  in the manner described above. The signals read from each of the columns can be readout sequentially or in parallel using a column addressing circuit  244 . Pixel signals (Vrst, Vsig) corresponding to the readout reset signal and integrated charge signal are provided as respective outputs Vout 1 , Vout 2  of the column readout circuit  242  where they are subtracted in differential amplifier  246 , digitized by analog-to-digital converter (ADC)  248 , and sent to an image processor circuit  250  for image processing. 
       FIG. 3  shows more details of one example of the arrangement of the rows and columns  249  of pixels  150  in the array  230 . Each column  249  includes multiple rows of pixels  150 . Signals from the pixels  150  in a particular column  249  can be readout to sample and hold circuitry  261  associated with the column  249  (part of circuit  242 ) for acquiring the pixel reset Vrst and integrated charge Vsig signals. Signals stored in the sample and hold circuits  261  can be read sequentially column-by-column to the differential amplifier  246  ( FIG. 2 ), which subtracts the reset and integrated charge signals and sends them to the analog-to-digital converter  248  ( FIG. 2 ). Alternatively, a plurality of analog-to-digital converters  248  may also be provided, each digitizing sampled and held signals from one or more columns  249 . 
       FIG. 4  illustrates portions of three sample and hold circuits  261  of  FIG. 3  in greater detail. Each sample and hold circuit  261  holds a set of signals, e.g., a reset signal Vrst and an integrated charge signal Vsig from a desired pixel. For example, a reset signal Vrst of a desired pixel connected to column line  170  is stored on capacitor  226  and the integrated charge signal Vsig from column line  170  is stored on capacitor  228 . A front side of capacitor  226  is switchably coupled to the column line  170  through switch  222  and a backside of capacitor  226  is switchably coupled to amplifier  248  through switch  218 . A front side of capacitor  228  is switchably coupled to the column line  170  through switch  220  and a backside of capacitor  228  is switchably coupled to amplifier  248  through switch  216 . The front side of capacitor  226  is switchably coupled to the front side of capacitor  228  through crowbar switch  239 . The backside of capacitor  226  is switchably coupled to the backside of capacitor  228  and to a reference voltage Vref source through clamp switch  299 . 
     Each sample and hold circuit  261  is coupled to amplifier  248  having first and second inputs. The first input of amplifier  248  is coupled to a first output of amplifier  248  through a capacitor  278  and a switch  279  to provide a first feedback circuit. The second input of amplifier  248  is coupled to a second output of amplifier  248  through a capacitor  276  and a switch  277  to provide a second feedback circuit. 
     The CMOS imager of  FIGS. 1-4  has identical correlated double sampling and holding timing for all columns over an entire row. Thus, all of the pixels in a row are readout at substantially the same time. The simplified correlated double sampling and column read out timing is depicted in  FIG. 5 . 
     Thus, to begin a readout operation, a logic high clamp signal c 1  is provided to clamp switch  299  thereby coupling the backsides of capacitors  226 ,  228  to a reference voltage source Vref. When a reset signal Vrst is read from the pixel  150 , a logic high SHR signal is provided to the gate of switch  222  thereby coupling the front side of capacitor  226  to the column line  170 . When the readout of the reset signal Vrst from the pixel  150  is complete, a logic low SHR signal is provided to the gate of switch  222  thereby uncoupling the front side of capacitor  226  from the column line  170 . Thus, a reset signal Vrst has been sampled and stored on capacitor  226 . 
     After the reset Vrst signal is read from pixel  150 , an integrated charge signal Vsig is readout. When the integrated charge signal Vsig is read from pixel  150 , a logic high SHS signal is provided to the gate of switch  220  thereby coupling the front side of capacitor  228  to the column line  170 . When the readout of the integrated charge signal Vsig from the pixel  150  is complete, a logic low SHS signal is provided to the gate of switch  220  thereby uncoupling the front side of capacitor  228  from the column line  170 . Thus, an integrated charge signal Vsig has been sampled and stored on capacitor  228 . 
     When the readout operation is complete, a logic low clamp signal c 1  is provided to clamp switch  299  thereby uncoupling the backsides of capacitors  226 ,  228  from the reference voltage source Vref. 
     After a row of pixels has been readout, sampled, and held, then, generally in column order, the sample and hold circuits  261  output their stored signals to the amplifier  248 . When reading from a first sample and hold circuit  261 , a logic high control signal Φamp is provided to the feedback circuits to close switch  279  to couple the first output of amplifier  248  through capacitor  278  to its first input and to close switch  277  to couple the second output of amplifier  248  through capacitor  276  to its second input. A logic high crowbar control signal, e.g., crowbar 1  for the sample and hold circuit  261  associated with the first column, is also provided to the sample and hold circuit  261  being readout to close the associated crowbar switch  239 , thereby coupling the front side of capacitor  226  to the front side of capacitor  228 . A logic high control signal, e.g., c 1  for the sample and hold circuit  261  associated with the first column, is also provided to the sample and hold circuit  261  being readout to close switch  218  and switch  216 , thereby coupling the backside of capacitor  226  to the first input of amplifier  248  and coupling the backside of capacitor  228  to the second input of amplifier  248 . 
     After the reset and integrated charge signals have been readout to amplifier  248 , a logic low control signal Φamp is provided to the feedback circuits to open switch  279  and uncouple the first output of amplifier  248  from capacitor  278  and to open switch  277  and uncouple the second output of amplifier  248  from capacitor  276 . A logic low crowbar control signal (e.g., crowbar  1  for the first column) is provided to the sample and hold  261  being readout to open the associated crowbar switch  239 , thereby uncoupling the front side of capacitor  226  from the front side of capacitor  228 . A logic low control signal e.g., c 1 , is also provided to the sample and hold  261  being readout to open switch  218  and switch  216 , thereby uncoupling the backside of capacitor  226  from the first input of amplifier  248  and uncoupling the backside of capacitor  228  from the second input of amplifier  248 . Thus, a correlated double sampled signal is provided as output from amplifier  248  resulting from the input of the integrated charge and reset signals to the amplifier  248 . After a row of sample and hold circuits  261  have been readout, a next of row of pixels  150  in the pixel array  230  are sample, held, and then readout through the amplifier  248 . 
       FIG. 6  illustrates a modified pixel array  230 ′ that uses 4-way shared pixel circuitry comprising four pixels in neighboring columns and which desirably omits a row select transistor in the readout circuit for the shared pixel circuits. The pixel array  230 ′ is an alternative to the pixel array  230 . The pixel array  230 ′ is comprised of even columns that include pixels  450   a - d  and odd columns that include pixels  451   a - d . Although pixel array  230 ′ is depicted as including three columns and four rows, the pixel array  230 ′ is representative of a pixel array having any plurality of rows and columns. The columns of the pixel array  230 ′ are labeled Y(m+1), Y(m), and Y-1(m+1) and the rows of pixel array  230 ′ are labeled X(n), X(n+1), X(n+2), and X(n+3). 
     In array  230 ′ pixels are diagonally grouped by color into a pixel circuit; thus, green pixels are grouped together and blue and red pixels are grouped together. A green pixel circuit, for example PixelCircuit 1 , is comprised of pixels  451   a ,  450   b ,  451   c , and  450   d . The green pixel circuit PixelCircuit 1  also includes a reset transistor  484  and a source follower transistor  486 . A blue and red pixel circuit, for example PixelCircuit 2 , is comprised of pixels  450   a ,  451   b ,  450   c , and  451   d . The blue and red pixel circuit PixelCircuit 2  also includes a reset transistor  485  and a source follower transistor  487 . In operation, the green pixel circuit PixelCircuit 1  is readout, row by row, through a single column line, e.g., Col Y(m+1) and the blue and red pixel circuit PixelCircuit 2  is readout, row by row, through a single column line, e.g., Col Y(m). No row select transistors are used in the readout circuit to couple the source follower transistors  486 ,  487  to a column line. 
     Pixel array  230 ′ also includes transfer transistor control lines associated with each row of the array  230 ′, e.g., TX X(n) for pixels in row X(n) associated with transfer transistors  490   a  and  491   a . Additionally, pixel array  230 ′ includes reset transistor control lines associated with each group of four rows of the array, e.g., RST X(n) for pixels in rows X(n), X(n+1), X(n+2), and X(n+3), associated with reset transistors  484 ,  485 . Moreover, pixel array  230 ′ includes column pull up (Col_Pu) transistors  498  to control coupling a Vaa-pix voltage to a column line  496 ,  497 . 
       FIG. 7  depicts a simplified correlated double sampling and column read out timing for the pixel array  230 ′ of  FIG. 6 . To begin a readout operation of a row X(n), at a time t 1 , a row address X(n) is provided to row addressing circuit  234  and column addressing circuit  244  of  FIG. 2 . A Col_Pu signal is applied to transistors  498  to couple lines  496 ,  497  to a voltage (e.g., Vaa-pix signal level) and therefore to activate the reset transistors  484 ,  485 . At time t 2 , a logic high RST signal is provided to the reset line RST X(n), thereby placing a reset charge on one of a source or drain of reset transistors  484 ,  485 . The floating diffusion regions  494 ,  495  are reset by this operation. At time t 3 , a logic low Col_Pu signal is applied to transistors  498  to turn off transistors  498  and to deactivate reset transistors  484 ,  485 , no longer resetting diffusion regions  494 ,  495 . Time t 3  occurs approximately 250-750 ns after time t 2  occurs, preferably 500 ns. 
     At time t 4 , a logic high VLN_EN control signal is provided to the gates of column line transistors  491 ,  492 , thereby creating a pull down circuit on the associated column lines, e.g.,  496 ,  497 . Time t 4  occurs 50-100 ns after time t 3 , preferably 70 ns. After time t 4 , a logic high SHR signal is strobed to sample and hold a reset signal Vrst readout of the floating diffusion regions  494 ,  495  into sample and hold circuitry. The SHR strobe lasts approximately 1-2 μs, preferably 1.5 μs. A logic high TX(n) then is strobed, which closes transfer transistors  491   a ,  490   a  and couples the photodiodes  462  to their associated floating diffusion regions  494 ,  495 , thereby transferring the accumulated charge from the photodiode  462  to their associated floating diffusion regions  494 ,  495 . The TX strobe lasts approximately 500-1000 ns, preferably 750 ns, ending at time t 5 . A logic high SHS signal is strobed to sample and hold accumulated charge read from the floating diffusion regions  494 ,  495  into sample and hold circuitry. The SHS signal begins to be strobed before the TX strobe has completed, e.g., before time t 5 . The strobe of the SHS signal lasts approximately 1-2 μs, preferably 1.5 μs and ends at time t 6 . At time t 7 , a logic low VLN_EN signal is provided thereby no longer creating a pulldown circuit on the associated column line. Time t 7  occurs approximately 50-100 ns, preferably, 70 ns, after time t 6 , e.g., the completion of the SHS strobe. Subsequently, a logic high Col_Pu signal and a logic low RST(n) signal are provided. Thus, a reset signal and a charge accumulation signal are sampled from the pixel array  230 ′. 
     At t 8 , a rolling shutter operation occurs. A row address X(n+m) is provided to row addressing circuit  234  and column addressing circuit  244  of  FIG. 2 , which is used for a rolling shutter. After time t 8 , a logic high RST(n+m) signal and a logic high TX(n+m) are provided. The strobe of the TX(n+m) signal occurs while the RST(n+m) is provided with a logic high signal. After the rolling shutter operation ends, e.g., at time t 9 , the next row of the pixel array is sampled, e.g., row n+1. The pixel array continues to be readout, row by row, until substantially all of the rows of the pixel array have been readout. Thus, a reset signal and a charge accumulated signal are read out from the pixel array. Further, a rolling shutter has been toggled. 
     With the pixel array  230 ′ ( FIG. 6 ) PixelCircuit 1 , PixelCircuit 2 , are comprised of zigzagged pixels in two neighboring columns, so the pixel circuits are asymmetric and are difficult to significantly reduce in size. 
     It is desirable to have a shared pixel circuit that is more compact and of reduced size. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a conventional imager pixel. 
         FIG. 2  is a block diagram of a conventional imager device. 
         FIG. 3  is a block diagram of a portion of an array of pixels illustrated in  FIG. 2  and an associated column readout circuit. 
         FIG. 4  is a conventional sample and hold circuit. 
         FIG. 5  is a simplified timing diagram associated with operation of the circuitry of  FIGS. 1-4 . 
         FIG. 6  is a block diagram of a diagonally shared pixel circuit. 
         FIG. 7  is a simplified timing diagram associated with operation of the circuitry of  FIG. 6 . 
         FIG. 8  is a block diagram of a vertically shared pixel circuit in accordance with an example embodiment disclosed herein. 
         FIG. 9  is simplified timing diagram associated with operation of the circuitry of  FIG. 8 . 
         FIG. 10  is a block diagram representation of a processor-based camera system incorporating a CMOS imaging device in accordance with an embodiment disclosed herein. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following detailed description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments that may be practiced. These embodiments are described in sufficient detail to enable those of ordinary skill in the art to make and use them, and it is to be understood that structural, logical, or procedural changes may be made. 
     Embodiments described herein provide a shared pixel circuit which omits a row select transistor in the readout circuit of a shared pixel and which reduces the size and complexity required by the shared pixel array depicted in  FIG. 6 . By providing a vertically shared (i.e., within the same column) pixel circuit, the overall size of the pixel array can be reduced. With a pixel circuit being shared vertically instead of across columns, associated readout circuitry is less complex. Thus, pixel circuits are symmetrical and can be reduced in size. Furthermore, the pixel circuits can also be readout quicker than the pixel circuit of  FIG. 6 . 
       FIG. 8  illustrates a pixel array  800  comprising vertically 4-way shared pixel circuitry, each comprising four pixels in a same column in accordance with an example embodiment. The pixel array  800  is comprised of even columns that include pixels  850   a - d  and odd columns that include pixels  851   a - d . Although pixel array  800  is depicted as including three columns and four rows, the pixel array  800  is representative of a pixel array having any plurality of rows and columns. The columns of the pixel array  800  are labeled Y(m+1), Y(m), and Y-1(m+1) and the rows of pixel array  800  are labeled X(n), X(n+1), X(n+2), and X(n+3). 
     In illustrated embodiment, pixels are vertically grouped by column into a shared pixel circuit; thus, four pixels in a column are grouped together. A first shared pixel circuit, for example PixelCircuit 1 ′, is comprised of pixels  850   a ,  850   b ,  850   c , and  850   d . The first pixel circuit PixelCircuit 1 ′ also includes a reset transistor  884  and a source follower transistor  896 . PixelCircuit 1 ′ does not include a row select transistor. A second shared pixel circuit, for example PixelCircuit 2 ′, is comprised of pixels  851   a ,  851   b ,  851   c , and  851   d . The second pixel circuit PixelCircuit 2 ′ also includes a reset transistor  885  and a source follower transistor  897  and does not include a row select transistor. 
     Each shared pixel circuit, e.g., PixelCircuit 1 ′ has a plurality of pixels, and at least two of the plurality of pixels are of a same color. For example, as depicted in  FIG. 8 , PixelCircuit 1 ′ includes two green pixels  850   b ,  850   d . Additionally, PixelCircuit 1 ′ includes two pixels of a second same color, e.g., pixels  850   a ,  850   c  are red. Similarly, PixelCircuit 2 ′ includes two green pixels  851   a ,  851   c  and two blue pixels  851   b ,  851   d . All of the plurality of pixels of the shared pixel circuit are in a same column of pixels. For example, the pixels of PixelCircuit 1 ′ are all in column Y(m+1). Each column of pixels in array  230 ′ includes a plurality of pixel circuits. 
     In an aspect, the pixel array  800  includes a plurality of ground (GND) lines that run in a vertical direction of the array. These ground lines are connected throughout the array  800  at various locations to a ground source. Including a plurality of GND lines that are relatively locally connected to a ground source reduces noise. Pixel array  800  includes column pull up (Col_Pu) transistors  498  to control coupling a Vaa-pix voltage to a column line  488 ,  489 . 
       FIG. 9  depicts a simplified correlated double sampling and column read out timing for the pixel array  800  of  FIG. 8 . To begin a readout operation of a row X(n), at a time t′ 1 , a row address X(n) is provided to row addressing circuit  234  and column addressing circuit  244   FIG. 2 . At time t′ 2 , a logic high RST signal is provided to the reset line RST X(n), thereby placing a charge on one of a source or drain of reset transistors  884 ,  885 . The floating diffusion regions  494 ,  495  are reset. At time t′ 3 , a logic high Col_PU signal is provided to transistors  498  thereby coupling the lines  488 ,  489  to a voltage, e.g., Vaa_pix voltage level and enabling diffusion regions  494 ,  495  to be reset (via the reset transistors  884 ,  885 ). In an aspect, time t′ 3  occurs approximately 250-750 ns after time t′ 2  occurs, preferably 500 ns. Before time t′ 4  occurs, a logic low Col_Pu signal is provided to transistors  498  thereby uncoupling the lines  488 ,  489  from the voltage, e.g., Vaa_pix voltage level, and disabling diffusion regions  494 ,  495  from being further reset. 
     At time t′ 4 , a logic high VLN_EN control signal is provided to the gates of transistors  491 ,  492  thereby creating a pull down circuit on the associated column lines, e.g.,  488 ,  489 . In one aspect, time t′ 4  occurs approximately 50-100 ns after time t 3 , preferably 70 ns. After time t′ 4 , a logic high SHR signal is strobed to sample and hold a reset signal read from the floating diffusion regions  494 ,  495  into a sample and hold circuit. In an aspect, the SHR strobe lasts approximately 1-2 μs, preferably 1.5 μs. A logic high TX(n) is strobed which closes transfer transistors  891   a ,  890   a  and couples the photodiodes  462  to their associated floating diffusion regions  494 ,  495  transferring the accumulated charge from the photodiodes  462  to their associated floating diffusion regions  494 ,  495 . In an aspect the TX(n) strobe lasts approximately 50-100 ns, preferably 70 ns, and ends at time t′ 5 . A logic high SHS signal is strobed to sample and hold the accumulated charge read from the floating diffusion regions  494 ,  495  into a sample and hold circuit. In a preferred approach, the SHS signal begins to be strobed before time t′ 5 , e.g., before the TX(n) strobe has completed. In an aspect, the strobe of the SHS signal lasts approximately 1-2 μs, preferably 1.5 μs, and ends at time t′ 6 . At time t′ 7 , a logic low VLN_EN is provided thereby no longer creating a pulldown circuit on the associated column line. In an aspect time t′ 7  occurs approximately 50-100 ns, preferably, 70 ns, after the completion of the SHS strobe. Subsequently, a logic low RST(n) signal is provided. Thus, a reset signal and a charge accumulation signal are sampled from the pixel array. After that, the Col_Pu is enabled with RST(n) at low to reset the floating diffusion regions  494 ,  495  to a low potential, which turns off the source follower transistor on the nth row. 
     At time t′ 8 , a rolling shutter operation begins. A row address X(n+m) is provided to row addressing circuit  234  and column addressing circuit  244  ( FIG. 2 ), which is used to implement a rolling shutter. After time t′ 8 , the logic high RST(n+m) signal and a logic high TX(n+m) are provided to reset the floating diffusion regions  494 ,  495  and photodiodes  462  to a high potential and fully deplete the photodiodes  462 . In an aspect, the strobe of the TX(n+m) signal occurs while the RST(n+m) is provided with a logic high signal; the Col_Pu is high and keeps the RST (n+m) at low to turn off the source follower on the (n+m)th row. After an initial aspect of the rolling shutter operation ends at time t′ 9 , the next row of the pixel array is sampled, e.g., row n+1. As conventionally known, the pixel array continues to be readout, row by row, until substantially all of the rows of the pixel array have been readout. 
       FIG. 10  is a block diagram representation of processor system that may include imaging device  1101  having the pixel array  800  ( FIG. 8 ) and associated readout circuitry as described with respect to the various embodiments described herein. The processor system could, for example, be a camera system  1190 . A camera system  1190  generally comprises a shutter release button  1192 , a view finder  1196 , a flash  1198  and a lens system  1194  for focusing an image on the pixel array  800  of imaging device  1101 . A camera system  1190  generally also comprises a central processing unit (CPU)  1110 , for example, a microprocessor for controlling camera functions which communicates with one or more input/output devices (I/O)  1150  over a bus  1170 . The CPU  1110  also exchanges data with random access memory (RAM)  1160  over bus  1170 , typically through a memory controller. The camera system  1190  may also include peripheral devices such as a removable memory  1130 , which also communicates with CPU  1110  over the bus  1170 . Imager device  1101  is coupled to the processor system and includes a pixel array  800  as described along with respect to  FIGS. 8-9 . Other processor systems which may employ imaging devices  800  besides cameras, including computers, PDAs, cellular telephones, scanners, machine vision systems, and other systems requiring an imager operation. 
     While the embodiments have been described and illustrated with reference to specific example embodiments, it should be understood that many modifications and substitutions can be made. Although the embodiments discussed above describe specific numbers of transistors, photodiodes, conductive lines, etc., they are not so limited. For example, the above embodiments are not limited to vertical (single column) with internal reset and no row select of a 4 way shared pixel and could be applied to 2 way shared, 3 way shared, 5 way shared, etc. Accordingly, the claimed invention is not to be considered as limited by the foregoing description but is only limited by the scope of the claims.