Patent Description:
While the pulsating nature of the illumination is not a problem for the human eye, which cannot detect pulses at the frequencies used to control the LEDs, the pulses present challenges when taking a picture of a scene, or a video with a typical digital sensor when the scene is illuminated by one or more LEDs being driven using PWM. The LEDs operate over a wide range of frequencies, and duty cycles. Further, when multiple LEDs are operating, the light sources are typically out of sync with one another. Hence, when taking a picture of a scene, or a video with a typical digital sensor or even a digital sensor with High Dynamic Range (HDR), there is a distinct probability that a particular frame capture either misses a pulse or set of pulses entirely, or saturates and blooms into neighboring pixels, destroying information. In a single photo snapshot, the picture can be simply wrong or not representative of the scene. In a video stream, one can obtain random blinking of steady light sources, missing parts of LED signage rendering the sign unreadable, or improper interpretation of signals which are actually blinking.

When taking a digital image of a scene with LEDs operated in such a manner, an HDR exposure is typically needed to capture the various shadows, mid-tones, and highlights (and extremely bright output of the LEDs). This HDR image typically translates to a very short exposure within a larger frame period to not saturate and bloom in the LED portion of the picture. This results in a flickering of the LED where from frame to frame, the "on" time of the LED source is either caught or missed by the short exposure. This flickering presents significant problems in systems such as self-driving automobile systems when operating at night, as missed frames mean that the system is blind for the period of the frame.

<CIT> discloses an imaging system that includes: an Illumination unit configured to emit illumination light for illuminating a subject; a light receiving unit in which pixels are arranged in two-dimensionally, each pixel being configured to receive light and generate an electrical signal by performing photoelectric conversion of the light; a readout unit configured to sequentially read out the electrical signal from the light receiving unit for every horizontal line; and an illumination controller configured to keep intensity of the illumination light emitted from the illumination unit constant in at least part of the readout period, where the readout unit reads out the horizontal line of the light receiving unit in one frame or one field period, and is configured to variably control an illumination time of the illumination light emitted from the illumination unit, outside of the readout period.

<CIT> discloses a solid state imaging device that includes a plurality of pixels stored in a one-dimensional or two-dimensional array, each of the plurality of pixels including a photodiode receiving light and producing photocharges. The device includes an overflow gate coupled to the photodiode and transferring photocharges that overflow the photodiode during storage operation, and a storage capacitor element that stores the photocharges transferred by the overflow gate during the storage operation.

<CIT> describes further examples of exposing an image sensor with a pulsed light source.

The present invention provides a system, according to claim <NUM>, which includes a pulsating light source and an apparatus for taking moving pictures. The apparatus according to the present invention includes a rectangular imaging array, a plurality of column processing circuits, and a controller. The rectangular imaging array is characterized by a plurality of rows and columns of ultra-high dynamic range (UHDR) pixel sensors and a plurality of readout lines, and a plurality of row select lines. Each column processing circuit is connected to a corresponding one of the plurality of readout lines. The controller causes the rectangular imaging array to measure a plurality of images of a scene that is illuminated by a pulsating light source characterized by an illumination period, during which an illumination pulse having an illumination pulse duration is generated. Each of the images generated in a frame period includes an exposure period and a dead period, the dead period being less than the illumination pulse duration.

In accordance with the invention, the exposure period is not synchronized with the illumination period.

In accordance with the invention, the UHDR pixels comprise a floating diffusion node, a main photodiode, and a parasitic photodiode associated with the floating diffusion node.

It may be that the controller causes the rectangular imaging array to be readout in a rolling shutter mode.

It may be that the controller causes the rectangular array to be readout in a global shutter mode.

The disclosure also provides UHDR pixels which comprise a photodiode and a capacitor that captures charges overflowing from the photodiode when the photodiode saturates.

The disclosure also provides a UHDR pixel which include a photodiode, a floating diffusion node, a buffer connected to the floating diffusion node that produces a pixel output signal having a voltage that is a monotonic function of a voltage on the floating diffusion node, a bit line gate that connects the pixel output signal to the bit line in response to a row select signal, a first reset gate that connects the floating diffusion node to a first reset voltage source in response to a reset signal, a first transfer gate that connects the photodiode to the floating diffusion node in response to a first transfer signal, an overflow capacitor connected to the floating diffusion node via a second transfer gate that connects the overflow capacitor to the floating diffusion node in response to a second transfer signal; and an overflow transfer gate that connects the photodiode to the overflow capacitor in response to an overflow transfer gate signal. In another aspect of the invention, each UHDR pixel further includes a second reset gate that connects the photodiode and the overflow capacitor to a reset voltage without applying the reset voltage to the floating diffusion node.

The present invention also includes a method, according to claim <NUM>, for operating a camera for taking moving pictures of a scene being illuminated by a pulsating light source. The camera has a rectangular imaging array characterized by a plurality of rows and columns of UHDR pixel sensors, and a controller that causes the rectangular imaging array to measure a plurality of images of the scene illuminated by the pulsating light source, the pulsating light source being characterized by an illumination period, during which an illumination pulse having an illumination pulse duration is generated. The method includes generating each of the images in a frame period which includes an exposure period and a dead period, the dead period is less than the illumination pulse duration.

It may be that the UHDR pixel sensors have sufficient dynamic range to capture the images if the exposure period includes a plurality of illumination pulses or the exposure period is equal to the illumination period minus a dark period.

It may be that the rectangular array is readout in a global shutter mode.

It may be that the rectangular array is readout in a rolling shutter mode.

To simplify the following discussion, a pixel sensor is defined to be a circuit that converts light incident thereon to an electrical signal having a magnitude that is determined by the amount of light that was incident on that circuit in a period of time, referred to as the exposure. The pixel sensor has a gate that couples that electrical signal to a readout line in response to a signal on a row select line.

A rectangular imaging array is defined to be a plurality of pixel sensors organized as a plurality of rows and columns of pixel sensors. The rectangular array includes a plurality of readout lines and a plurality of row select lines, each pixel sensor being connected to one row select line and one readout line, the electrical signal generated by that pixel being connected to the readout line associated with that pixel in response to a signal on the row select line associated with that pixel sensor.

The manner in which the present invention provides its advantages can be more easily understood with reference to <FIG>, which illustrates a two-dimensional imaging array according to one embodiment of the present invention. Rectangular imaging array <NUM> includes sensors such as pixel sensor <NUM>. Each pixel sensor has a main photodiode <NUM> and a parasitic photodiode <NUM>. The manner in which the pixel sensor operates will be discussed in more detail below. The reset circuitry and amplification circuitry in each pixel is shown at <NUM>. The pixel sensors are arranged as a plurality of rows and columns. Exemplary rows are shown at <NUM> and <NUM>. Each pixel sensor in a column is connected to a readout line <NUM> that is shared by all of the pixel sensors in that column. Each pixel sensor in a row is connected to a row select line <NUM> which determines if the pixel sensor in that row is connected to the corresponding readout line.

The operation of rectangular imaging array <NUM> is controlled by a controller <NUM> that receives a pixel address to be readout. Controller <NUM> generates a row select address that is used by row decoder <NUM> to enable the readout of the pixel sensors on a corresponding row in rectangular imaging array <NUM>. The column amplifiers are included in an array of column amplifiers <NUM> which execute the readout algorithm, which will be discussed in more detail below. A set of calibration sources <NUM> allow differences in the column amplifiers to be measured and corrected. All of the pixel sensors in a given row are readout in parallel; hence there is one column amplification and analog-to-digital converter (ADC) circuit per readout line <NUM>. The column processing circuitry will be discussed in more detail below.

When rectangular imaging array <NUM> is reset and then exposed to light during an imaging exposure, each photodiode accumulates a charge that depends on the light exposure and the light conversion efficiency of that photodiode. That charge is converted to a voltage by reset and amplification circuitry <NUM> in that pixel sensor when the row in which the pixel sensor associated with that photodiode is readout. That voltage is coupled to the corresponding readout line <NUM> and processed by the amplification and ADC circuitry associated with the readout line in question to generate a digital value that represents the amount of light that was incident on the pixel sensor during the imaging exposure.

A motion picture is a sequence of frames, each frame comprising a readout of the entire rectangular array of pixel sensors. There is a time period in each frame in which light is not measured by the imaging array. This time will be referred to as the dead time of the array. The maximum exposure for an array is determined by the frame rate and the dead time.

There are two types of readout schemes, referred to as global shutter and rolling shutter. In a global shutter scheme, all rows of the array are reset simultaneously, exposed to light from the image. After a predetermined exposure time, the accumulated photocharge is transferred to the floating diffusion node in each pixel sensor, the transferred charge is measured one row at a time.

In a rolling shutter camera, each row is processed sequentially in the array. The processing starts by transferring the photocharge to the floating diffusion node, which ends the current exposure for that row. The charge is then readout and the photodiode(s) are reset after a predetermined time determined by the desired exposure time and allowed to accumulate photocharge for the next frame.

In the prior art, both of these schemes have a common exposure time for each row of pixels, and that exposure is less than the maximum exposure time allowed for the chosen frame rate. The time between the maximum possible exposure and the actual exposure time will be referred to as the dead time in the following discussion. In a flashing illumination application, any illumination pulse that occurs during this dead time is either lost or only partially effective in illuminating the scene of interest. If the camera is not synchronized with the illumination source, the scene will exhibit flickering. Furthermore, some of the frames can be lost altogether, if the pulse for that frame occurred entirely within the dead time. In an autonomous driving vehicle, such lost frames can result in the computer being blinded, which poses significant safety issues for self-driving vehicles.

The present invention is based on the observation that lost frames can be avoided by using an exposure scheme in which the shutter is effectively open during essentially all of the exposure, except for the small period of time in which the charge is being transferred to the floating diffusion node to be measured. Even in the case in which the readout time is significant, the next frame will have been started and the photodiodes will be accumulating light, and hence, no pulse will be missed.

The challenge with this type of scheme lies in the potential for over-exposure. If the scene is being illuminated by multiple pulsing non-synchronized light sources, multiple pulses can be captured in the same exposure leading to blooming in the image at bright locations. The present invention overcomes this problem by using an UHDR pixel design that has sufficient dynamic range to capture the light received by each pixel even if a conventional pixel would saturate during the excessive exposure. For the purposes of the present discussion, an UHDR pixel sensor is defined to be a pixel sensor having one or more photodiodes for measuring light received by the pixel sensor during an exposure. The range of exposures that can be measured by an UHDR pixel sensor is greater than the range of exposures that can be measured by one of the photodiodes in the sensor without causing that photodiode to saturate.

The dynamic range of the pixel is the ratio of the largest light exposure the pixel can measure without saturating divided by the smallest light exposure that the pixel can measure over the noise. In a non-UHDR pixel, the photodiode will saturate at the highest exposure and any remaining light exposure is lost. In a multi-photodiode UHDR pixel, when the photodiode saturates, a second photodiode having a lower light to photocharge conversion ratio is used to measure the light or the photocharge that overflows from the first photodiode is captured on a capacitor and added to the photocharge on the saturated photodiode. In a single photodiode UHDR pixel, the charge that overflows is captured on a capacitor and added to the charge remaining in the photodiode at the readout of the UHDR pixel.

The challenge in using an UHDR pixel array lies in providing the capacitor or the second photodiode within a conventional fabrication process without substantially changing the area of the pixel array. Consider embodiments in which a conventional second photodiode is added to each pixel. The preferred ratio of photo-conversion ratios is about <NUM>:<NUM>. Hence, the second photodiode would need to have an area that is <NUM>/<NUM>th that of the conventional photodiode. Making such a small photodiode presents significant challenges in current fabrication processes. If the light conversion efficiency per unit area of the second photodiode is reduced to increase its area to accommodate the fabrication limitations, then the area of the pixel will be increased significantly leading to additional costs.

Similarly, the addition of a capacitor for each pixel on which the overflow charge is stored requires a second transfer gate connecting the photodiode to the floating diffusion node and space for the capacitor. Again there is an increase in area, and the associated costs.

The preferred embodiment of an UHDR for use in the present invention utilizes a parasitic diode that is associated with a floating diffusion node in each pixel to provide the second photodiode. The manner in which this UHDR achieves its advantages can be more easily understood with reference to <FIG> is a schematic drawing of a typical prior art pixel sensor in one column of pixel sensors in an imaging array. Pixel sensor <NUM> includes a photodiode <NUM> that measures the light intensity at a corresponding pixel in the image. Initially, photodiode <NUM> is reset by placing gate <NUM> in a conducting state and connecting floating diffusion node <NUM> to a reset voltage, Vr. Gate <NUM> is then closed and photodiode <NUM> is allowed to accumulate photoelectrons. A potential on gate <NUM> sets the maximum amount of charge that can be accumulated on photodiode <NUM>. If more charge is accumulated than allowed by the potential on gate <NUM>, the excess charge is shunted to the power rail through gate <NUM> to avoid blooming.

After photodiode <NUM> has been exposed, the charge accumulated in photodiode <NUM> is typically measured by noting the change in voltage on floating diffusion node <NUM> when the accumulated charge from photodiode <NUM> is transferred to floating diffusion node <NUM>. Floating diffusion node <NUM> is characterized by a capacitance represented by capacitor <NUM>'. In practice, capacitor <NUM>' is charged to a voltage Vr and isolated by pulsing the reset line of gate <NUM> prior to floating diffusion node <NUM> being connected to photodiode <NUM>. The charge accumulated on photodiode <NUM> is transferred to floating diffusion node <NUM> when gate <NUM> is opened. The voltage on floating diffusion node <NUM> is sufficient to remove all of this charge, leaving the voltage on floating diffusion node <NUM> reduced by an amount that depends on the amount of charge transferred and the capacitance of capacitor <NUM>'. Hence, by measuring the change in voltage on floating diffusion node <NUM> after gate <NUM> is opened, the accumulated charge can be determined.

If the reset voltage on floating diffusion node <NUM> is sufficiently reproducible, then a single measurement of the voltage on floating diffusion node after reset is sufficient. However, noise results in small variations in the reset voltage. If this noise is significant, a correlated double sampling algorithm is utilized. In this algorithm, floating diffusion node <NUM> is first reset to Vr using reset gate <NUM>. The potential on floating diffusion node <NUM> is then measured by connecting source follower <NUM> to readout line <NUM> by applying a select signal to line <NUM> to a readout gate. This reset potential is stored in column amplifier <NUM>. Next, gate <NUM> is placed in a conducting state and the charge accumulated in photodiode <NUM> is transferred to floating diffusion node <NUM>. It should be noted that floating diffusion node <NUM> is effectively a capacitor that has been charged to Vr. Hence, the charge leaving photodiode <NUM> lowers the voltage on floating diffusion node <NUM> by an amount that depends on the capacitance of floating diffusion node <NUM> and the amount of charge that is transferred. The voltage on floating diffusion node <NUM> is again measured after the transfer. The difference in voltage is then used to compute the amount of charge that accumulated during the exposure.

The present invention is based on the observation that a pixel of the type discussed above can be modified to include a second parasitic photodiode that is part of the floating diffusion node and has a significant photodiode detection efficiency. This second light detector does not significantly increase the size of the pixel, and hence, the present invention provides the advantages of a two-photodiode pixel without significantly increasing the pixel size.

To distinguish the parasitic photodiode from photodiode <NUM>, photodiode <NUM> and photodiodes serving analogous functions will be referred to as the "conventional photodiode". Refer now to <FIG>, which illustrates a pixel sensor in which the parasitic photodiode is utilized in an image measurement. To simplify the following discussion, those elements of pixel sensor <NUM> that serve functions analogous to those discussed above with respect to <FIG> have been given the same numeric designations and will not be discussed further unless such discussion is necessary to illustrate a new manner in which those elements are utilized. In general, parasitic photodiode <NUM> has a detection efficiency that is significantly less than that of photodiode <NUM>. The manner in which the ratio of the photodiode detection efficiencies of the two photodiodes is adjusted is discussed in more detail in co-pending <CIT>, <CIT>. In one exemplary embodiment, the ratio of the conversion efficiency of the main photodiode to the parasitic photodiode is <NUM>:<NUM>. Other embodiments in which this ratio is <NUM>:<NUM> or <NUM>:<NUM> are useful.

The manner in which pixel sensor <NUM> is utilized to measure the intensity of a pixel in one embodiment of the present invention will now be explained in more detail. The process may be more easily understood starting from the resetting of the pixel after the last image readout operation has been completed. Initially, main photodiode <NUM> is reset to Vr and gate <NUM> is closed. This also leaves floating diffusion node <NUM> reset to Vr. If a correlated double sampling measurement is to be made, this voltage is measured at the start of the exposure by connecting floating diffusion node <NUM> to column amplifier <NUM>. Otherwise, a previous voltage measurement for the reset voltage is used. During the image exposure, parasitic photodiode <NUM> generates photoelectrons that are stored on floating diffusion node <NUM>. These photoelectrons lower the potential on floating diffusion node <NUM>. At the end of the exposure, the voltage on floating diffusion node <NUM> is measured by connecting the output of source follower <NUM> to column amplifier <NUM>, and the amount of charge generated by parasitic photodiode <NUM> is determined to provide a first pixel intensity value. Next, floating diffusion node <NUM> is again reset to Vr and the potential on floating diffusion node <NUM> is measured by connecting the output of source follower <NUM> to column amplifier <NUM>. Gate <NUM> is then placed in the conducting state and the photoelectrons accumulated by main photodiode <NUM> are transferred to floating diffusion node <NUM>. The voltage on floating diffusion node <NUM> is then measured again and used by column amplifier <NUM> to compute a second pixel intensity value.

If the light intensity on the corresponding pixel was high, main photodiode <NUM> will have overflowed; however, parasitic photodiode <NUM>, which has a much lower conversion efficiency, will have a value that is within the desired range. On the other hand, if the light intensity was low, there will be insufficient photoelectrons accumulated on parasitic photodiode <NUM> to provide a reliable estimate, and the measurement from main photodiode <NUM> will be utilized.

The dead time associated with an array based on the pixel sensors shown in <FIG> in a rolling shutter system is the time needed to readout the pixel sensor. This time corresponds to the time to readout the parasitic photodiode and then the main photodiode in the manner described above.

Ideally, each pixel sensor is identical to every other pixel sensor, is reset to the same voltage during readout, and generates a signal value of zero when no light impinges on rectangular imaging array <NUM>. In addition, under ideal conditions each column application circuit is identical to every other column amplification circuit. There are four analog conversion factors in the chain of processing from light exposure of a photodiode to a final digital value. These are the light-to-charge conversion efficiencies of the photodiodes. The charge-to-voltage conversion is in the pixel reset and amplification circuitry <NUM>, and there is the voltage amplification circuitry in the column processing circuitry. Differences in these analog conversion factors give rise to fixed pattern noise (FPN). The FPN can depend on factors that change over time and also depend on the temperature of the imaging array when the exposure is taken.

In addition to FPN, there are other noise factors that must be reduced to obtain a noise factor that is small compared to the shot noise. Reset noise is an example of this type of noise. The manner in which reset noise is created can be more easily understood with reference to <FIG>, which illustrates a prior art pixel sensor. <FIG> is a schematic drawing of a typical prior art pixel sensor in one column of pixel sensors in an imaging array. Pixel sensor <NUM> includes a photodiode <NUM> that measures the light intensity at a corresponding pixel in the image. Initially, photodiode <NUM> is reset by placing gate <NUM> in a conducting state and connecting floating diffusion node <NUM> to a reset voltage, Vr. Gate <NUM> is then closed and photodiode <NUM> is allowed to accumulate photoelectrons. A potential on gate <NUM> sets the maximum amount of charge that can be accumulated on photodiode <NUM>. If more charge is accumulated than allowed by the potential on gate <NUM>, the excess charge is shunted to the power rail through gate <NUM>.

The present invention is based on the observation that a pixel of the type discussed above can be modified to include a second parasitic photodiode that is part of the floating diffusion node and has significant photodiode detection efficiency. This second light detector does not significantly increase the size of the pixel, and hence, the present invention provides the advantages of a two-photodiode pixel without significantly increasing the pixel size.

It should be noted that the photocharge for the main photodiode cannot be transferred to the floating diffusion node until after the parasitic photodiode photocharge has been measured. Once the parasitic photocharge is measured, the floating diffusion node is reset and the main photodiode photocharge is transferred to the floating diffusion node. At this point, the main photodiode could be reset through gate <NUM>; however, the exposure cannot be started until the charge on the floating diffusion node has been readout and the floating diffusion node has been reset. Once the floating diffusion node has been reset and reset voltage measured, the exposure for the next frame can begin. Hence, the dead time is the total time needed to readout the pixel. Hence, as long as the dead time is less than the duration of one light pulse, the next light pulse will not have been missed. Accordingly, the present invention can provide a significant advantage in a rolling shutter system.

A global shutter imager using a two-photodiode pixel sensor has a significantly longer dead time, and hence, is not the preferred embodiment for such pixel sensors. In a global shutter arrangement, the entire array must be readout before the next frame exposure can start. Hence, the dead time is the time needed to readout the entire frame. If there are N lines in the array, the dead time will be N times the dead time in the rolling shutter embodiment. However, if the dead time is still significantly less than the light pulse duration, no frames will be completely lost.

While two photodiode UHDR pixel sensors are not optimal for a global shutter array with an extended exposure, other forms of UHDR pixels can be utilized in a global shutter array and still provide the advantage of a reduced dead time. Refer now to <FIG>, which illustrates an UHDR pixel. Pixel <NUM> includes a photodiode <NUM> that generates the photocharge during an exposure. A transfer gate <NUM> allows the accumulated charge to be transferred from photodiode <NUM> to floating diffusion node <NUM> in response to signal Tx1. For the purposes of the present discussion, a floating diffusion node is defined to be an electrical node that is not tied to a power rail, or driven by another circuit. Floating diffusion node <NUM> is characterized by a parasitic capacitor <NUM> having a capacitance, CFD. Floating diffusion node <NUM> may also have a parasitic photodiode; however, the pixel sensors are shielded such that light does not reach the floating diffusion node in this embodiment. When gate <NUM> is in the conducting state, the photocharge collected on photodiode <NUM> alters the voltage of floating diffusion node <NUM> from a reset voltage value that is set prior to the transfer. The amount of reduction in the floating diffusion node voltage provides a measure of the photocharge that was transferred.

A reset gate <NUM> is used to set the voltage on floating diffusion node <NUM> prior to the charge being transferred. The voltage on floating diffusion node <NUM> is amplified by a source follower transistor <NUM>. When pixel <NUM> is to be readout, a signal on gate transistor <NUM> connects the output of source follower transistor <NUM> to a bit line <NUM> that is shared by all of the pixel sensors in a given column. For the purposes of the present discussion, a bit line is defined to be a conductor that is shared by a plurality of columns of pixel sensors and carries a voltage signal indicative of the voltage at the floating diffusion node in a pixel sensor that is connected to the bit line through a transfer gate. Each bit line terminates in a column processing circuit that includes a bit-line amplifier <NUM>.

Pixel <NUM> also includes an overflow capacitor <NUM> that collects the photocharge generated by photodiode <NUM> after photodiode <NUM> saturates. At the beginning of an exposure, photodiode <NUM> and overflow capacitor <NUM> are set to a reset voltage determined by Vr. As photocharge accumulates on photodiode <NUM>, the voltage on photodiode <NUM> decreases until photodiode <NUM> reaches a value that is determined by the gate voltage on gate <NUM>. Any additional photocharge flows through gate <NUM> and onto the combination of overflow capacitor <NUM>, parasitic capacitor <NUM> (i.e., the parasitic capacitance of floating diffusion node <NUM>), via overflow line <NUM> and the parasitic capacitances of gate <NUM>, which remains in a conducting state throughout the exposure.

At the end of the exposure, the overflow charge will have been split between overflow capacitor <NUM> and parasitic capacitor <NUM>. The voltage on the floating diffusion node will have decreased by an amount that depends on the overflow charge and the sum of the capacitances of capacitors <NUM> and <NUM>. If either gates <NUM> or <NUM> are opened, the charge remaining on photodiode <NUM> will also be swept on parasitic capacitor <NUM> and reset gate <NUM>, and hence, the voltage on floating diffusion node <NUM> will reflect the total photocharge generated during the exposure. If gates <NUM> and <NUM> are now placed in a non-conducting state, the voltage on floating diffusion node <NUM> will continue to represent all of the photocharge generated during the exposure.

It should be noted the charge transfer from photodiode <NUM> to floating diffusion node <NUM> can be carried out simultaneously on all pixels in the array. Furthermore, photodiode <NUM> and overflow capacitor <NUM> are isolated from floating diffusion node <NUM> and can be reset via gate <NUM>. As soon as gate <NUM> goes non-conducting, a new exposure can start. During the new exposure, the voltages on the floating diffusion nodes can be readout one line at a time, and hence, the dead time is the time to transfer the charge from photodiode <NUM> to floating diffusion node <NUM>, which is small compared to the duration of a light pulse that illuminates the scene.

As each pixel sensor is readout, the voltage on floating diffusion node <NUM> is reset to Vr and measured for use in measuring the photocharge for the current exposure. Finally, gate <NUM> is placed in the conducting state, so that the overflow photocharge can be stored on the parallel connected capacitors.

In the above-described embodiments, the voltage on the floating diffusion node is readout using a source follower buffer. However, other forms of buffers could be utilized for this purpose including capacitive trans-impedance amplifiers.

Claim 1:
A system comprising a pulsating light source and an apparatus for taking moving pictures, the apparatus comprising:
a rectangular imaging array (<NUM>) comprising a plurality of rows (<NUM>, <NUM>) and columns of ultra high dynamic range pixel sensors (<NUM>) and a plurality of readout lines (<NUM>), and a plurality of row select lines (<NUM>);
a plurality of column processing circuits, each column processing circuit being connected to a corresponding one of said plurality of readout lines (<NUM>); and
a controller (<NUM>) that causes said rectangular imaging array (<NUM>) to measure a plurality of images of a scene being illuminated by the pulsating light source, the pulsating light source has an illumination period, during which an illumination pulse having an illumination pulse duration is generated, each of said plurality of images being generated in a frame period comprising an exposure period and a dead period;
wherein each pixel sensor has a main photodiode (<NUM>) used to measure light received by the pixel sensor (<NUM>) during an exposure, and a floating diffusion node;
characterized in that:
each pixel sensor comprises a parasitic photodiode associated with said floating diffusion node, the parasitic photodiode acting as a second photodiode and being used to measure light received by the pixel sensor (<NUM>) during the exposure, the second photodiode having a lower light to photocharge conversion ratio than the main photodiode wherein each pixel sensor provides a first pixel intensity value corresponding to a charge generated by the parasitic photodiode during the exposure and a second pixel intensity value corresponding to a charge generated by the main photodiode during the exposure;
and
each dead period is less than the illumination pulse duration; and
said exposure period is not synchronized with said illumination period.