Abstract:
An imaging system provides a serial video signal that is indicative of the intensity of the light. The imaging system has an array of pixel image sensors arranged in rows and columns. A control circuit is in communication with the rows of the array and the plurality of column switches. The control circuit generates reset control signals, transfer gating signals, pixel image sensor initiation signals for each selected row for controlling resetting, integration of photoelectrons generated from the light impinging upon the array of pixel image sensors, charge transfer of the photoelectrons from the photosensing devices to the charge storage device, and to activate the photoelectron sensing devices on each row to generate output signals from each of the pixel image sensors on a selected row. The control circuit generates the column selection signals for transfer of the output signals from selected rows to form a serial video output signal.

Description:
[0001]    This application is a continuation of and claims priority to pending U.S. patent application Ser. No. 11/998,960, filed Dec. 3, 2007, which claims priority under 35 U.S.C. §.119 to U.S. Provisional patent application Ser. No. 60/872,120, filed Dec. 1, 2006, all of which are herein incorporated by reference in their entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to solid-state image sensing devices, methods and circuits for operating solid state image sensing devices and an imaging system using the same. 
         [0004]    2. Description of Related Art 
         [0005]    Integrated circuit image sensors are finding applications in a wide variety of fields, including medical imaging, machine vision, robotics, guidance and navigation, automotive applications, and consumer products such as digital camera and video recorders. Imaging circuits typically include a two dimensional array of photo sensors. Each photo sensor includes one picture element (pixel) of the image. Light energy emitted or reflected from an object impinges upon the array of photo sensors. The light energy is converted by the photo sensors to an electrical signal. Imaging circuitry scans the individual photo sensors to readout the electrical signals. The electrical signals of the image are processed by external circuitry for subsequent display. 
         [0006]    Modern metal oxide semiconductor (MOS) design and processing techniques have been developed that provide for the capture of light as charge and the transporting of that charge within active pixel sensors and other structures so as to be accomplished with almost perfect efficiency and accuracy. 
         [0007]    One class of solid-state image sensors includes an array of active pixel sensors (APS). An APS is a light sensing device with sensing circuitry inside each pixel. Each active pixel sensor includes a sensing element formed in a semiconductor substrate and capable of converting photons of light into electronic signals. As the photons of light strike the surface of a photoactive region of the solid-state image sensors, free charge carriers are generated and collected. Once collected the charge carriers, often referred to as charge packets or photoelectrons are transferred to output circuitry for processing. 
         [0008]    An active pixel sensor also includes one or more active transistors within the pixel itself. The active transistors amplify and buffer the signals generated by the light sensing element to convert the photoelectron to an electronic signal prior to transferring the signal to a common conductor that conducts the signals to an output node. 
         [0009]    Active pixel sensor devices are fabricated using processes that are consistent with complementary metal oxide semiconductor (CMOS) processes. Using standard CMOS processes allows many signal processing functions and operation controls to be integrated with an array of active pixel sensors on a single integrated circuit chip. 
         [0010]    Refer now to  FIG. 1  for a more detailed discussion of an active pixel image sensor array  5  of the prior art. The photodiode  15  are formed within the surface a substrate. A floating diffusion  25  is formed within the substrate to function as capacitive storage nodes for hold charge accumulated within the photodiode&#39;s  15  depletion region. The transfer gate switches  20  are connected between the photodiode  15  and the floating diffusion  25  and is activated by the transfer gate signal  30  connected to the gate of the transfer gate switch  20 . The source of the reset transistor  35  is connected to the floating diffusion  25  and the drain of the reset transistor  35  is connected to the power supply voltage source VDD. The reset signal  50  is connected to the reset transistor  35  to activate the reset transistor  35  to connect the floating diffusion  25  to the power supply voltage source VDD to reset the floating diffusion to the voltage level of the power supply voltage source VDD. During the activation of the reset transistor  35 , the transfer gate switch  20  is activated to also reset the voltage level of the photodiode  15  to the voltage level of the power supply voltage source VDD and remove any residual photoelectrons from the depletion region of the photodiode  15 . 
         [0011]    The floating diffusion  25  is connected to the gate of the source follower transistor  40 . The drain of the source follower transistor  40  is connected to the power supply voltage source VDD and the emitter of the source follower transistor  40  is connected to the drain of the row select switch transistor  45 . The gate of the row select switch transistor  45  is connected to the row select signal  55 . The source follower transistor  40  acts to buffer the electrical signal created by the photoelectron charge collected in the floating diffusion  25 . 
         [0012]    The photons  17  that impinge upon the photodiode  15  are converted to photoelectrons and collected within the photodiode  15 . At the completion of an integration of the collection of the photoelectrons, the transfer gate signal  30  is activated to turn on the transfer gate switch  20  to transfer the collected photoelectrons to the storage node of the floating diffusion  25 . When the collected photoelectrons are retained at the floating diffusion  25  the row select signal  55  is activated to turn on the row select switch transistor  45  to gate the pixel conversion output electrical signal PIX_OUT to row bus  60 . The amplitude of pixel conversion output electrical signal PIX_OUT is indicative of the intensity of the light energy hv or the number of photons  17  absorbed by the photodiode  15 . Once the pixel output electrical signal PIX_OUT is read out the reset signal  50  is activated to turn on the reset transistor  35  and the photodiode  15  and the floating diffusion  25  are emptied of the photoelectrons. 
         [0013]    The pixel image sensors  10   a , . . . ,  10   b , . . . ,  10   m , . . . ,  10   n  are placed in columns and rows to form the array  5 . Each of the pixel image sensors  10   a , . . . ,  10   b , . . . ,  10   m , . . . ,  10   n  are structured as described above. The gate of the row select switch transistor  45   a , . . . ,  45   b , . . . ,  45   m , . . . ,  45   n  of each pixel image sensor  10   a , . . . ,  10   b , . . . ,  10   m , . . . ,  10   n  on each row of the array  5  is connected to the row select signal  55   a , . . . ,  55   n  generated by the row control circuit  65 . The source of each row select switch transistor  45   a , . . . ,  45   b , . . . ,  45   m , . . . ,  45   n  of each pixel image sensor  10   a , . . . ,  10   b , . . . ,  10   m , . . . ,  10   n  on each column of the array  5  is connected to a column sample and hold circuit  75   a , . . . ,  75   n  through the row buses  60   a , . . . ,  60   n.    
         [0014]    The drain of each of the reset transistors  35  of the each pixel image sensor  10   a , . . . ,  10   b , . . . ,  10   m , . . . ,  10   n  of the array  5  is connected to a power supply voltage source VDD through a distribution network to each pixel image sensor  10   a , . . . ,  10   b , . . . ,  10   m , . . . ,  10   n . The gate of the reset transistor  35  of each pixel image sensor  10   a , . . . ,  10   b , . . . ,  10   m , . . . ,  10   n  on each row of the array  5  is connected to the reset signal  50   a , . . . ,  50   n  generated by the row control circuit  65  for selectively resetting the floating diffusion  25  and the photodiode  15  of each pixel image sensor  10   a , . . . ,  10   b , . . . ,  10   m , . . . ,  10   n . The gate of each transfer gate switch  20  of each pixel image sensor  10   a , . . . ,  10   b , . . . ,  10   m , . . . ,  10   n  on each row of the array  5  is connected to the transfer gate signal  30   a , . . . ,  30   n  generated by the row control circuit  65  for transferring the photoelectrons from photodiode  15  to the floating diffusion  25  of each pixel image sensor  10   a , . . . ,  10   b , . . . ,  10   m , . . . ,  10   n.    
         [0015]    The floating diffusion  25  acts as the photoelectron storage node for each pixel image sensor  10   a , . . . ,  10   b , . . . ,  10   m , . . . ,  10   n  and is connected to the gate of the source follower source follower transistor  40 . The drain of the source follower transistor  40  is connected to the power supply voltage source VDD and the source is connected to the drain of the row select switch transistor  45 . The gate of the row select switch transistor  45  is connected to the row select signal  55  and the source is connected to the row bus  60   a , . . . ,  60   n  for connection to the column sample and hold/image readout circuit  70 . 
         [0016]    The row select signal  55  activates the row select switch transistor  45  to transfer the voltage at the source of the source follower transistor  40  to the row bus  60   a , . . . ,  60   n  for connection to the column sample and hold/image readout circuit  70 . The voltage at the source of the source follower transistor  40  is proportional to the number of photons  17  that impinge upon each photodiode  15  of each pixel image sensor  10   a , . . . ,  10   b , . . . ,  10   m , . . . ,  10   n.    
         [0017]    The column sample and hold circuit  75   a , . . . ,  75   n  combines the column pixel row operation (pixel reset, row select) and the column operation (the photo generation, photo sensing). The sample and hold signal SH  84  and the clamp signal  83  are activated and deactivated by the column sample and hold/image readout circuit to respectively activate the switches SW 1   77  and SW 2   80  to capture the pixel output electrical signal PIX_OUT indicative of the level of the intensity of the light energy  17  present on each of the photodiode  15  of each pixel image sensor  10   a , . . . ,  10   b , . . . ,  10   m , . . . ,  10   n . This combination causes the output voltage of the column sample and hold circuit  75   a , . . . ,  75   n  to be equal to the differential voltage of pixel reset level and photo conversion electrical signal level, i.e., V out =V rst −V sig . During the pixel readout, switch SW 3    81  controlled by column select signal COL_SEL  82  transfers the differential voltage through the column bus COL_BUS 85 to the video amplifier  92  of the image readout circuit  90  that applies the gain factor and offset correction factor to the output signal. The output of video amplifier  92  is the analog output that is digitized by an analog-to-digital converter  94 . The output of the analog-to-digital converter  94  is the digital data word  95  that is transferred to an image processor. 
         [0018]    “Self-Scanned Image Sensors Based on Charge Transfer by the Bucket-Brigade Method”, Weimer, et al., IEEE Transactions on Electron Devices, November 1971, Vol.: 18, Issue: 11, pp.: 996-1003 describes solid-state image sensors which are internally scanned by charge transfer offer an alternative to sensors based on x-y addressing. Shift registers are employed for the x-y addressing. 
         [0019]    “Transversal-Readout Architecture for CMOS Active Pixel Image Sensors”, Miyatake, et al., IEEE Transactions on Electron Devices, Vol. 50, no. 1, pp: 121-129, January 2003 provides a novel architecture for CMOS active pixel image sensors (APS&#39;s), which eliminates the vertically striped fixed pattern noise (FPN). An array of transversal-readout APS is shown with two vertical (row) shift registers for addressing the rows of the array and a horizontal shift register for addressing the columns of the array. One of the with two vertical (row) shift registers is for selecting a row for reset and the other is of the with two vertical (row) shift registers is for selecting the row for readout. 
         [0020]    U.S. Pat. No. 6,037,979 (Yonemoto) teaches a solid-state imaging device with a vertical shift register for addressing the row of the imaging device and a horizontal shift register that selects gating switches to transfer the conversion signal from each pixel of a selected row to a single amplifier. 
         [0021]    U.S. Pat. No. 6,184,928 (Kannegundla, et al.) provides split shift register addressing for array applications such as imaging arrays. A fast shift register is coupled to a slow shift register by a combinatorial circuit having inputs from the fast shift register and the slow shift register to providing the selected address. 
         [0022]    U.S. Pat. No. 6,570,615 (Decker, et al.) teaches a pixel readout scheme for image sensors that has a single differential to single-ended amplifier. The signals from each pixel are correlated double sampled passed through the select switches to the single differential to single-ended amplifier to an analog multiplexer, and thence to a programmed gain amplifier to an analog-to-digital converter. 
         [0023]    U.S. Pat. No. 6,903,768 (Ohsawa, et al.) describes a solid state image sensor device with unit cells of the image sensing cell array having horizontal rows and vertical columns that are read by turning on an address register by means of the vertical shift register. Those of the vertical signal lines in the optical black pixel region are connected with each other through a wiring. Since the vertical signal lines in the optical black pixel region are connected with each other by a wiring, even if outputs from an optical black pixel region vary in the pixels, the outputs are made averaged and uniform and a variation in fixed pattern noises between the horizontal lines are reduced. 
         [0024]    U.S. Pat. No. 6,961,088 (Kameshima, et al.) teaches a sensor array having a sample and hold circuit connected to an analog multiplexer. The signal from a selected column of sensors is applied through the multiplexer to an analog-to-digital converter. A shift register provides a selection of the column for each of the sensors on a selected row. 
         [0025]    U.S. patent application 2001/0033337 (Sakuragi) provides an image pickup apparatus that includes a two-dimensional image pickup area, a vertical line selector for selecting a reading row in the image pickup area, vertical signal lines arranged in columnar direction, for reading a detection signal emitted by a photodiode located in a selected row, and a horizontal selection transistor for continuously reading detection signals carried by the vertical signal lines and writing the signals to a horizontal signal line arranged like a row in a matrix. The horizontal signals are generated by a vertical shift register for selecting the row of the matrix. The signals from each photodiode are applied to a vertical signal line that are applied to a single amplifier. Each column has a sample and hold circuit and a select switch to apply the signals from the sample and hold circuit to the amplifier. A horizontal shift register select which of the switches and thus the columns that are to be selected. 
         [0026]    U.S. patent application 2002/0001037 (Miyawaki, et al.) describes a photoelectric conversion device that has sensors arranged in columns and rows. The columns and rows are addressed by a horizontal and vertical shift register. The sense signals are selectively applied to a single amplifier to create an output signal. 
         [0027]    U.S. patent application 2002/0044211 (Tujii, et al.) teaches an image sensing device with a vertical shift register for the addressing of rows of the array of the image sensing device. An analog multiplexer receives signals from the columns of the image sensing device and applies them to an analog-to-digital converter. 
         [0028]    U.S. patent application 2005/0012836 (Guidash) provides an image sensor that includes pixel output analog multiplexers that enables sample and hold of the signals from either of the two columns of pixels into either of the associated column circuits. 
         [0029]    U.S. patent application 2005/0168606 (Yonemoto) illustrates a solid-state imaging device with a shift register used for a horizontal (row) scanning device and a charge holding device at the bottom of each row with switches to connect to a serial output amplifier. 
         [0030]    U.S. patent application 2004/0080650 (Hwang, et al.) describes a CMOS image sensor single chip integrated with an RF transmitter. 
       SUMMARY OF THE INVENTION 
       [0031]    An object of this invention is to provide an imaging system with circuits for controlling operation of an array of pixel image sensors that sense light impinging upon the pixel image sensors to provide a serial video signal that is indicative of the intensity of the light. 
         [0032]    To accomplish at least this object, an imaging system for creating an image of an object has an image sensor and a control circuit fabricated on a surface of a substrate. The image sensor includes an array of pixel image sensors arranged in rows and columns upon the substrate for conversion of photons of the light impinging upon the image sensor to photoelectrons. Each of the pixel image sensors has an photoelectron sensing device such as a source follower transistor circuit having a high impedance input connected to detect presence of the photoelectrons on a charge storage device incorporated within the pixel image sensor, an output line containing an output voltage signal that has a magnitude related to a number of the photoelectrons, and a gated power supply source input to selectively receive a pixel image sensor initiation signal to activate the photoelectron sensing device to generate the output voltage signal. At the end of all the columns of the pixel images sensors are column switches. Each column switch is connected such that the output line of each photoelectron sensing device of each pixel image sensor is selectively connected to transfer each output signal from each pixel image sensor of a selected row. 
         [0033]    The control circuit is in communication with the rows of the array of plurality of pixel image sensors and the plurality of column switches. The control circuit generates reset control signals, transfer gating signals, pixel image sensor initiation signals for each selected row for controlling resetting, integration of photoelectrons generated from the light impinging upon the array of pixel image sensors, charge transfer of the photoelectrons from the photosensing devices to the charge storage device, and to activate the photoelectron sensing devices on each row to generate output signals from each of the pixel image sensors on a selected row. The control circuit generates the column selection signals for transfer of the output signals from the selected row. 
         [0034]    The control circuit generates the reset control signals, transfer gating signals, pixel image sensor initiation signals, and column selection signals to provide a double sampling of each pixel image sensor of each selected row. A first sampling of the double sampling is a reset level of each pixel image sensor on the selected row and a second sampling of the double sampling is a signal level related to the number of photoelectrons. The column selections signals activate each column selection switch to serially form each first sampling from each pixel image sensor into a reset output signal for transfer and serially form each second sampling from each pixel image sensor into a photon magnitude output signal for transfer serial video output signal. The control circuit further generates a vertical frame synchronization signal to indicate a beginning of transfer of a frame image prior to transfer of the serially formed first sampling and second sampling of a first selected row of said array of a plurality of pixel image sensors. 
         [0035]    The array of the pixel image sensors has a row address shift register and column address shift register. The row address shift register is in communication with each row of the plurality of pixel image sensors to sequentially transfer the reset control signals, transfer gating signals, and pixel image sensor initiation signals to each pixel image sensor on the selected row. The column address shift register is in communication with each column of the plurality of pixel image sensors to sequentially transfer the column selection signal to each pixel image sensor to activate each column switch. 
         [0036]    The imaging system additionally has a pixel reference voltage generator in communication with one of the column switches not connected to a column of the pixel image sensors for generating a pixel reference voltage. The pixel reference voltage is multiplexed with each of the first samplings and each of the second samplings of the pixel image sensors of a selected row to provide a serial output signal. 
         [0037]    The column switches are connected to an amplifier to receive the serial output signal, condition, and amplify the serial output signal for transfer to an external processing circuit. The external processing circuit is in communication with the image sensor to demodulate, perform an analog-to-digital signal conversion, and determine a digital video signal from the first samplings and the second samplings indicative of the image of the light impinging upon the array of a plurality of pixel image sensors. The external processing circuit comprises a buffer memory circuit for retaining digital video signal from the first samplings, the second samplings, and the pixel reference voltage to await processing for determining the digital video signal. A video driver is in communication with the video amplifier to receive, buffer and modulate the serial output signal for transmission to the external processing circuit. 
         [0038]    Each of the pixel image sensors includes a reset triggering switch in communication with the charge storage device to place the pixel image sensor to a reset voltage level after integration and sensing of the photoelectrons. The reset triggering switch is further in communication with the row control circuit to receive one of the reset control signals and the pixel image sensor initiation signal for activation of the reset triggering switch for resetting the pixel image sensors on a selected row. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0039]      FIG. 1  is a functional diagram of an image sensor system of the prior art. 
           [0040]      FIG. 2  is a schematic of a pixel image sensor incorporated in an image sensor system of this invention. 
           [0041]      FIG. 3  is a functional diagram of an image sensor system of this invention. 
           [0042]      FIG. 4  is a block diagram of an image sensor system of this invention. 
           [0043]      FIG. 5  is a timing diagram of the operation of the pixel image sensor incorporated in the image sensor system of this invention. 
           [0044]      FIGS. 6   a ,  6   b , and  6   c  are timing diagrams of the operation of the image sensor system of this invention. 
           [0045]      FIGS. 7 and 8  are flow charts for a method for capturing an image of an object by an image sensor of this invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0046]    Image sensor applications such as medical endoscopy require minimum chip size while maintaining imager quality and good electromagnetic interference characteristics. The image sensor system of this invention provides an imager structure that requires only a clock input and a single analog sensor and system control circuit. The image sensor transmits a video signal to a receiving image processing system via a transmission media, such as a cable that is subject to interference, without loosing the signal integrity. 
         [0047]    The pixel image sensor of the image sensor system of this invention has an active pixel sensor circuit similar to that described in U.S. Pat. No. 5,920,345 (Sauer). The pixel image sensor  200 , as shown in  FIG. 2 , has a gated power supply voltage source distribution line  125  that is coupled to the drain terminals of the reset MOS transistor  115  and the source follower MOS transistor  120 . The gated power supply voltage source distribution line  125  is connected through a row control circuit to selectively connect the drain terminals of the reset MOS transistor  115  and the source follower MOS transistor  120  to a power supply voltage source VDD. The source follower transistor  120  is connected to a column output line  140 . When the gated power supply voltage source distribution line  125  is activated, the pixel image sensor is provided power for resetting the photodiode sensor  100  and the floating diffusion capacitance storage node  105 . The gated power supply voltage source distribution line  125  further provides power for the source follower MOS transistor  120  to generate an output voltage on the output line  140  having a magnitude related to the magnitude of the photoelectrons present on the floating diffusion capacitance storage node  105 . 
         [0048]    In operation, photons,  145  impinge upon the photodiode  100  and are converted to photoelectrons. The gate of the reset MOS transistor  115  is connected to the reset signal line  130 , which, when activated turns on the reset MOS transistor  115  to connect the floating diffusion capacitance storage node  105  to the gated power supply voltage source distribution line  125  to reset the floating diffusion capacitance storage node  105 . Simultaneously, the transfer gate signal line  135  is activated to reset or remove photoelectrons from the depletion region of the photodiode. After the reset signal line  130  is deactivated, the photodiode is exposed to the photons for conversion and integration of photoelectrons. At the end of the integration period, the transfer gate signal line  135  that is connected to the gate of the transfer gate  110  is activated. The transfer gate  110  has its drain connected to the photodiode  100  and its source to the floating diffusion capacitance storage node  105 . When activated the transfer gate  110  is turned on to allow the photoelectrons that are resident in the depletion layer of the photodiode  100  to migrate to the floating diffusion capacitance storage node  105 . The voltage level created by the photoelectrons is sensed by the source follower MOS transistor  120  to create the output conversion signal  140  that is transferred to a column bus line of an array. 
         [0049]    Multiple pixel image sensors  200  of  FIG. 2  are shown in  FIG. 3  arranged in rows and columns to form an array  205 . A gated power supply voltage source row distribution lines  210   a , . . . ,  210   n  are each connected commonly to each pixel image sensor  200   a , . . . ,  200   b , . . . ,  200   m , . . . ,  200   n  of each one of the rows of the pixel image sensors  200   a , . . . ,  200   b , . . . ,  200   m , . . . ,  200   n . When the gated power supply voltage source row distribution line  210   a , . . . ,  210   n  is activated the power supply voltage source is connected as described above to the drain terminals of the reset MOS transistor and the source follower MOS transistor of each of the pixel image sensors  200   a , . . . ,  200   b , . . . ,  200   m , . . . ,  200   n.    
         [0050]    The row reset gating signal lines  215   a , . . . ,  215   n  are each connected to each reset signal line of each of the pixel image sensors  200   a , . . . ,  200   b , . . . ,  200   m , . . . ,  200   n  on each row of the array  205 . When the gated power supply voltage source row distribution line  210   a , . . . ,  210   n  and the row reset gating signal line  215   a , . . . ,  215   n  are activated, the photodiodes and the floating diffusion capacitance storage node of the pixel image sensors  200   a , . . . ,  200   b , . . . ,  200   m , . . . ,  200   n  of the selected row of the array  205  are set to the reset voltage level. 
         [0051]    The row transfer gating signal lines  220   a , . . . ,  220   n  are each connected to each transfer gate signal line of each of the pixel image sensors  200   a , . . . ,  200   b , . . . ,  200   m , . . . ,  200   n . After the floating diffusion capacitance storage node of the pixel image sensors  200   a , . . . ,  200   b , . . . ,  200   m , . . . ,  200   n  of the selected row of the array  205  are reset and the photons of the impinging light are converted to photoelectrons, the row transfer gating signal line  220   a , . . . ,  220   n  of a selected row is activated to transfer the photoelectrons to the floating diffusion capacitance storage node of each of the pixel image sensor  200   a , . . . ,  200   b , . . . ,  200   m , . . . ,  200   n  of the selected row. Since the gated power supply voltage source row distribution line  210   a , . . . ,  210   n  of the selected row is activated, the source follower of the pixel image sensors  200   a , . . . ,  200   b , . . . ,  200   m , . . . ,  200   n  of the selected row transfers the pixel output signal to each of the column signal buses  225   a , . . . ,  225   n  for connected to the column switches  235 . 
         [0052]    The row control circuit  230  is a shift register based circuit that receives appropriate timing, reset, and control signals from the sensor and system control circuit  250  to generate the timing for the gated power supply voltage source row distribution lines  210   a , . . . ,  210   n , the row reset gating signal lines  215   a , . . . ,  215   n , and the row transfer gating signal lines  220   a , . . . ,  220   n  to control operation of the array  205  of pixel image sensors  200   a , . . . ,  200   b , . . . ,  200   m , . . . ,  200   n . Refer now to  FIG. 6  for a description of these signal timings for activation of two rows of the array  205 . At the beginning of each successive activation (τ 0 ), the gated power supply voltage source row distribution line  210   n −1 and  210   n  for each row to be activated is initiated and the row transfer gating signal lines  220   n −1 and  220   n  are activated to turn on the transfer gates of each pixel image sensor  200   a , . . . ,  200   b , . . . ,  200   m , . . . ,  200   n  of first the selected row (n−1) for the first activation period and the second selected row (N) for the successive activation period. At the time τ 1 , the row transfer gating signal lines  220   n −1 and  220   n  are deactivated and at the time τ 2 , the row reset gating signal lines  215   n −1 and  215   n  are deactivated. During the time period from the time .tau. 2  to the time .tau. 3 , the selected row of pixel image sensors  200   a , . . . ,  200   b , . . . ,  200   m , . . . ,  200   n  are converting and integrating the photons impinging upon the array to photoelectrons. Further during the time period from the time τ 2  to the time τ 3 , the source follower of the pixel image sensors  200   a , . . . ,  200   b , . . . ,  200   m , . . . ,  200   n  of the selected row n−1 and n transfers the pixel output signal for the reset voltage level to each of the column signal buses  225   a , . . . ,  225   n . Between the times τ 3  and τ 4 , the row transfer gating signal lines  220   n −1 and  220   n  are activated to transfer the photoelectrons integrated during the period from .tau. 2  to .tau. 3  to the floating diffusion capacitance storage node of the pixel image sensors  200   a , . . . ,  200   b , . . . ,  200   m , . . . ,  200   n  of the selected row (n−1 or n). At the deactivation of the row transfer gating signal lines  220   n −1 and  220   n  at the time τ 4 , the source follower of the pixel image sensors  200   a , . . . ,  200   b , . . . ,  200   m , . . . ,  200   n  of the selected row n−1 and n transfers the pixel output signal for the pixel conversion signal voltage level to each of the column signal buses  225   a , . . . ,  225   n  until the time τ 5 . At the time τ 5 , the row reset gating signal line  215   n −1 and  215   n  is activated with the row transfer gating signal lines  220   n −1 and  220   n  to reset the pixel image sensor  200   a , . . . ,  200   b , . . . ,  200   m , . . . ,  200   n  of the selected row (n−1 or n). At the time τ 6 , the row transfer gating signal lines  220   n −1 and  220   n  is deactivated and at the time beginning time of the next cycle τ 0 , the gated power supply voltage source row distribution line  210   n −1 and  210   n  is deactivated. All the rows, except the activated row (n−1 or n), have their gated power supply voltage source row distribution lines  210   a , . . . ,  210   n  deactivated and their row reset gating signal line  215   a , . . . ,  215   n  signals activated to essentially place the photodiodes and the floating diffusion capacitance storage nodes of the pixel image sensors  200   a , . . . ,  200   b , . . . ,  200   m , . . . ,  200   n  of the non-selected rows of the array  205  at the ground reference voltage level. 
         [0053]    The pixel output signals placed on each of the column signal buses  225   a , . . . ,  225   n  are the inputs to the column switches  235 . Each column switch  240   a , . . . ,  240   n  sequentially connects the column signal buses  225   a , . . . ,  225   n  to the column pixel bus  255  to create the serial video output. Each row of the pixel image sensors  200   a , . . . ,  200   b , . . . ,  200   m , . . . ,  200   n  is doubly read, first to transfer the reset voltage level for the pixel image sensors  200   a , . . . ,  200   b , . . . ,  200   m , . . . ,  200   n  of the selected row and second to transfer the conversion voltage signal level for the pixel image sensors  200   a , . . . ,  200   b , . . . ,  200   m , . . . ,  200   n  of the selected row. The column control circuit  260  is essentially a shift register that sequentially provides the column switch activation signals to the column switches  240   a , . . . ,  240   n . The sensor and system control circuit  250  provides the necessary timing and control signals to the column control circuit  260  to generate the column switch activation signals at the appropriate time to generate the serial video output signal on the column pixel bus  255 . 
         [0054]    The sensor and system control circuit  250  is further connected to the column pixel bus  255  to provide the vertical synchronizing signal, the horizontal signal, and an intra-column synchronizing signal at the appropriate times to indicate the beginning of the scan of an array, beginning of the readout of each row, and the separation of the read out of the reset levels of a row and the read out of the conversion signal levels. 
         [0055]    The clock generator  280  provides the digital timing necessary for the sensor and system control circuit  250  to generate the control signals for the row control circuit  230  and the column control circuit  260  and to generate the vertical synchronizing signal, the horizontal signal, and an intra-column synchronizing signal. The clock generator  280  may integrated with the image sensor or generated externally and applied as an input signal to the image sensor. 
         [0056]    The column pixel bus  255  is connected to the video amplifier  270 . The video amplifier  270  receives the serial video output signal on the column pixel bus  255  to amplify and condition the serial video output signal for transfer to external video receiver circuit. The video amplifier  270  is a push pull current amplifier capable of driving the load of an external cable. An example of the external cable would be a 100 ohm cable with +/−5 mA maximum output current. The video amplifier  270  has an output  275  referenced to the power supply voltage source VDD for ground reference noise isolation. The current sources  271  and  272  at the input of the video amplifier have a very high ground reference noise rejection using a cascoded architecture. The output current of the video amplifier  270  is generated across the output resistor  273 . For the resistor  273  with a value of 500 ohms, the output current will be approximately 2 mA and 4 ma for reset level and saturation level, respectively. 
         [0057]    The pixel reference voltage generator  265  has a diode connected MOS transistor  267  connected to the source follower transistor  269 . The source of the source follower transistor  269  is connected to the reference column switch  245  to connect the pixel reference voltage generator  265  to the column pixel bus  255  in the periods between the accessing each of the column signal buses  225   a , . . . ,  225   n  to provide the reference level for the reset level and the conversion signal level. The pixel reference voltage generator  265  is placed close to the video amplifier  270 . The diode connected MOS transistor  267  connected to the source follower transistor  269  have dimensions chosen to guarantee lowest threshold voltage (Vt) drops compared to the minimum size pixel array transistors. The transmission gate reference column switch  245  is turned on when the clock is low while all the other column selects for the column signal buses  225   a , . . . ,  225   n  occur when clock is high. 
         [0058]    Alternatively, a more complicated output circuit (not shown) which allows switching the output between plus/minus (+/−) output current level to provide a double rate (2.times.) pixel rate carrier signal. The double rate pixel rate carrier signal would act as an amplitude modulation (AM). Depending on the frequency of any interfering signals, the output modulation rates greater than the double pixel rate could be chose. Further, other modulation techniques such as frequency modulation (FM) of the output could be chosen for improved interference suppression and be in keeping with the intent of this invention. 
         [0059]    The imager structure of this invention as described in  FIG. 3  is incorporated as a CMOS image sensor application specific integrated circuit (ASIC)  300  in an image sensor system of  FIG. 4 . Referring to  FIG. 4 , the CMOS image sensor ASIC  300  includes the imager array  205 . The row shift register and drivers  230  provides the row control signals to the image array  205 . The row pixel activation signal  210  selectively applies a gated power supply voltage source PIXVDD to each selected row of pixel images sensors of the image array  205 . The row reset signal line  215  selectively gates the voltage level of the gated power supply voltage source PIXVDD to the photodiode and the floating diffusion capacitance storage node of each pixel to reset each pixel prior to integration and conversion of the photon to photoelectrons. The row transfer gate signal  220  activates each transfer gate during the readout operation to transfer the photoelectrons from the photodiode to the floating diffusion capacitance storage node. 
         [0060]    The column shift register driver  260  provides the column switch controls to the column readout switches  235  to selectively and sequentially connect each of the column signal buses to the column pixel bus to provide the double sampling where the first sampling is the reset level of a selected row and the second sampling is the conversion signal level of the selected row. The serial video output signal of the column readout switches  235  are transferred on the column pixel bus  255  to the video amplifier  270 . 
         [0061]    The sensor and system control circuit  250  is connected to the row shift register and drivers  230  and the column shift register driver  260  to provide the control and the timing for the row pixel activation signal  210 , row reset signal line  215 , and row transfer gate signal  220 . Further, the sensor and system control circuit  250  is connected to the video amplifier  270  to provide the vertical synchronization signal, the horizontal synchronization signal, and the intra-column synchronization signal to synchronize the sampling signals of the serialized output signals. 
         [0062]    As noted above, the clock generator  280  provides the clocking signal for the sensor and system control circuit  250  for generating the appropriate timing and control signals. The clock generator  280  maybe an external circuit that generates a control signal  340  that is applied externally to the CMOS image sensor ASIC  300 . 
         [0063]    The video amplifier  270  will amplify and condition the serial video signal  255  for transmission as the video output signal  275 . The video driver  305  maybe included as a driver modulator to provide various output modulation rates and techniques for improved interference suppression. The video output transmission  275  maybe on a cable, for example within an endoscope, or as a radio frequency through the environment for a wireless communication of the image. 
         [0064]    The transmitted serial video output signal  275  is captured by the video processing system  310 . The video receiver receives the transmitted video signal  275  amplifies and conditions the video signal. If the video signal has been modulated according to one of the above described techniques, it is transferred to the video demodulator  320  for demodulation to recover the original serial video signal. The serial video signal is applied to an analog-to-digital converter  325  for conversion to digital video data. The digital video data to transferred to a buffer memory  330  for storage for further processing. Further, the synchronization signals are extracted to determine the timing for the digital video data. The digital signal processor  335  extracts the digitized reset voltage level, the digital conversion voltage level, and the reference voltage levels for each pixel on each row and determines the Pixel Level Value as: 
         [0000]      Pixel Level Value=(Δ Photon Conversion Levels &amp; Pixel Ref Levels)−(Δ Reset Levels &amp; Pixel Ref Levels)
 
         [0000]    The pixel level values are formatted to generate a digital video output signal  340  that is transferred for further processing, storage, and display. 
         [0065]    Refer now to  FIGS. 3 and 6   a  for a description of the timing of the operation of the image sensor of this invention. The clock generator  280  provides the clock timing signal for synchronizing the operation of the image sensor. At the beginning of the transfer of an image (prior to the time t 0 ) a vertical synchronization pulse is transferred by the sensor and system control circuit  250  to the column pixel bus  255  to denote the beginning of the transfer of a frame. 
         [0066]    The sensor and system control circuit  250  initiates the row control circuit  230  to generate the row pixel activation signal  210 , row reset signal line  215 , and row transfer gate signal  220  and generates the horizontal synchronization pulse during the period of time between the time t o  and the time t 1 . At the time between the time t 0  of each of the row access times, the row control circuit  230  maintains the reset signal to reset the floating diffusion capacitance storage node of each pixel. The row control circuit  230  sets the gated power supply voltage source row distribution lines  210  to the ground reference voltage level and the row transfer gating signal lines  220  is activated to essentially set the photodiode to the ground reference voltage level. At the time t 1 , the row control circuit  230  activates the gated power supply voltage source row distribution lines  210  and deactivates the row reset gating signal lines  215 . The sensor and system control circuit  250  activates the column control circuit  260  to activate the column select line  262  to sequentially turn on each column select line  240 . The period of each column select line  240  is approximately equal to that of the one half of the clock  280  cycle. During the remainder of the clock  280  cycle, the reference column switch  245  is activated to place the pixel reference voltage level at the serial video output line  275  between each of the reset voltage levels for each pixel of the selected row. 
         [0067]    During the period of time between the time t 1  and the time t 2 , the photodiodes of each pixel image sensors  200   a , . . . ,  200   b , . . . ,  200   m , . . . ,  200   n  of the selected row is exposed to the photons to allow conversion and integration of the photoelectrons. During the period of time between the time t 2  and the time t 3 , the intra-column synchronization signal generated by the sensor and system control circuit  250  to be placed on the video output  275 . In the period of time between the time t 2  and the time t 3 , the row transfer gating signal lines  220  is activated to activate the transfer gate of the pixel image sensors  200   a , . . . ,  200   b , . . . ,  200   m , . . . ,  200   n  of the selected row to transfer the photoelectrons from the photodiodes to the floating diffusion capacitance storage node of the pixel image sensors  200   a , . . . ,  200   b , . . . ,  200   m , . . . ,  200   n  of the selected row. The row transfer gating signal lines  220  is terminated at the time t 3 . 
         [0068]    Simultaneously, at the time t 3 , the sensor and system control circuit  250  activates the column control circuit  260  to activate the column select lines  262  to sequentially turn on each column select line  240  to transfer the conversion signal levels to the video output  275 . As described above, the period of each column select line  240  is approximately equal to that of the one half of the clock  280  cycle. During the remainder of the clock  280  cycle, the reference column switch  245  is activated to place the pixel reference voltage level at the serial video output line  275  between each of the conversion signal levels for each pixel of the selected row. The conversion signal levels are completed at the time t 4 . At the time t 5 , the row reset gating signal lines  215  and the row transfer gating signal line  220  are activated to reset the photodiodes and the floating diffusion capacitance storage node of each pixel image sensors  200   a , . . . ,  200   b , . . . ,  200   m , . . . ,  200   n  of a selected row. At the time t 6 , the gated power supply voltage source row distribution lines  210  are deactivated for the selected row and the next row is selected. The time period between the time t 5  and time t 6  is also the time of the horizontal synchronization pulse between the outputs of the selected rows. 
         [0069]      FIG. 6   b  illustrates an alternative to the video output signal  275 . The clock signal  280 , the gated power supply voltage source row distribution lines  210 , the row reset gating signal lines  215 , the row transfer gating signal lines  220 , and the column select lines  262  are as shown in  FIG. 6   a . The horizontal synchronization pulse is modified to have multiple pulses having a repetition rate equal to that of the clock signal  280 . The multiple pulse of the horizontal synchronization allows for a phase locking of the video output signal  275  in the video receiver. 
         [0070]    Refer now to  FIGS. 3 and 6   c  for a discussion of the vertical frame synchronization signal  285  generated at the beginning of the transfer of an image at the video output signal  275 . The sensor and system control circuit  250  has a counter that keeps track of the number of clock cycles  280 . The sensor and system control circuit  250  sends out the vertical frame synchronization signal  285  during the time period from the t 0  time t 1  to the row control circuit  230  and column control circuit  260  after counting the appropriate number of clock signals. This starts reading out the first row of the image array  205  during the time period from the t 1  to time t 2 . Each successive row is read out during the time period from the t 2  to time t 3 , with the last row (row n) read out during the time period from the t 3  to time t 4 . The sensor and system control circuit  250  then sends out another vertical frame synchronization signal  285  after the last row of the image array  205  is read out at the time t 4  to start the next frame. This is repeated for all succeeding frames. 
         [0071]    Since the image sensor described in this invention has only one video output signal  275 , it does not have a separate output line to provide a frame synchronization signal  285  and thus must share the serial video output  275 . The frame synchronization signal  285  now functions as a synchronization header signal indicating the beginning of one frame of an image being transferred as the video output signal  275 . The frame header synchronization signal  285  is shown in this example as a sequence of 4-clock cycle HIGH, followed by 4-clock cycle LOW. However, any appropriate coding for the frame synchronization signal  285  may be used and still be in keeping with the intent of this invention. At the completion of the frame synchronization head signal  285 , the video signals  290   a  for the first row are transferred, followed by the video signals for each successive row of the array  205 . After the video signals  290   n  for the last row of the array  205  are transferred, the synchronization header signal  285  for the next image frame is transferred indicating the beginning of the next frame of the image. 
         [0072]    In summary, the image sensor system of this invention provides an apparatus that performs the method shown in  FIGS. 7 and 8 . A vertical synchronization signal is generated and transmitted (Box  400 ) to demarcate the beginning of each new frame of an image, as described in  FIG. 6   c.    
         [0073]    A row counter is initialized (Box  405 ) to select (Box  410 ) the first row of an array of pixel image sensors as describe in  FIG. 2  that arranged in rows and columns. A gated power supply voltage source is applied to the row of pixel image sensors to activate (Box  415 ) the selected row (i). The row reset signal is activated to reset (Box  420 ) to reset the photodiode and the floating diffusion capacitance storage node of each pixel of the selected row. When the reset levels are established, the row transfer gating signal is activated to transfer (Box  425 ) the reset voltage level to the floating diffusion capacitance storage node. A source follower senses the reset level and transfers it to the column signal bus connected to each pixel of the selected row. Simultaneously, a horizontal synchronization pulse is transmitted (Box  430 ) on the video output signal. 
         [0074]    The column switches connected to all the column signal buses and to a reference voltage generator interleaves (Box  435 ) the reset voltage levels with a reference voltage level for transmission (Box  440 ) subsequent to the horizontal synchronization pulse on the video output signal. 
         [0075]    With the row transfer gating signal deactivated at the completion of the transmission (Box  440 ) of the interleaved reset levels and the reference voltage levels, the pixel image sensors of the selected row (i) convert the impinging photons to photoelectrons and integrate (Box  445 ) them within the depletion layer of the photodiode. The transfer gate of the pixel image sensors of the selected row is activated to transfer (Box  450 ) the photoelectrons to the floating diffusion capacitance storage node for sensing by the source follower to generate the photo conversion signal level at the column signal buses connected to each of the pixel image sensors of the selected row. During the transfer of the photoelectrons, an intra-column synchronization signal is transmitted (Box  455 ) on the video output signal. 
         [0076]    The column switches connected to all the column signal buses and to a reference voltage generator interleave (Box  460 ) the photo conversion voltage levels with a reference voltage level for transmission (Box  465 ) subsequent to the transmission (Box  455 ) of the intra-column synchronization pulse on the video output signal. 
         [0077]    The row counter is tested (Box  470 ) if all the rows have been reset, integrated, sensed, and readout. If there are rows of the pixel image sensors to be reset, integrated, sensed, and readout, the row counter is incremented (Box  475 ) and the next row is selected (Box  410 ) to be reset, integrated, sensed, and readout as described above. If all rows are scanned, the vertical synchronization pulse is transmitted (Box  400 ), the row counter initialized (Box  405 ), and the first row is selected to be reset, integrated, sensed, and readout as described above. 
         [0078]    The video output signal is formed of the transmission (Box  430 ) of the horizontal synchronization pulse, followed by the transmission (Box  440 ) of the reset voltage levels interleaved with the reference voltage level, then followed by the transmission (Box  455 ) of the intra-column synchronization signal, and the transmission (Box  465 ) of the photo conversion voltage levels interleaved with a reference voltage level. The intra-column synchronization signal is received (Box  520 ) and provides the synchronization with the horizontal synchronization pulse for the receiving (Box  525 ) of the photo conversion voltage levels with the reference voltage levels. The photo conversion voltage levels and the reference voltage levels are then converted (Box  530 ) to digital data representing the amplitudes of the photo conversion voltage levels and the reference voltage levels. The digital data representing the amplitudes of the photo conversion voltage levels and the reference voltage levels are then stored in the pixel level buffer  515 . The reset voltage levels, the photo conversion voltage levels, and the reference voltage levels are retrieved from the pixel level buffer  515  and the Pixel Level Value is determined (Box  540 ) by the formula: 
         [0000]      Pixel Level Value=(Δ Photon Conversion Levels &amp; Pixel Ref Levels)−(Δ Reset Levels &amp; Pixel Ref Levels)
 
         [0079]    While this invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the invention.