Low noise CMOS image sensor by stack architecture

#The present invention is generally related to image sensors, and more specifically, the present invention is directed to high dynamic range image sensors.

#Standard image sensors have a limited dynamic range of approximately 60 to 70 dB. However, the luminance dynamic range of the real world is much larger. Natural scenes often span a range of 90 dB and over. In order to capture the highlights and shadows simultaneously, HDR technologies have been used in image sensors to increase the captured dynamic range. The most common techniques to increase dynamic range is to merge multiple exposures captured with standard (low dynamic range) image sensors into a single linear HDR image, which has much larger dynamic range than a single exposure image.

#One of the most common HDR sensor solutions would be having multiple exposures into one single image sensor. With different exposure integration times or different sensitivities (for example by inserting neutral density filters), one image sensor could have 2, 3, 4 or even more different exposures in a single image sensor. Multiple exposure images are available in a single shot using this HDR image sensor. However, overall image resolution is decreased using this HDR sensor compared to a normal full resolution image sensor. For example, for an HDR sensor that combines 4 different exposures in one image sensor, each HDR image would be only a quarter resolution of the full resolution image.

#Non-limiting and non-exhaustive embodiments of the present invention are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified.

#FIG. 1 is a diagram illustrating one example of imaging system including a color pixel array in which each pixel circuit is a dual conversion gain circuit including a stacked architecture to achieve high dynamic range (HDR) imaging in accordance with the teachings of the present invention.

#FIG. 2 is a diagram illustrating one example of a pixel circuit with dual conversation gain implemented in a stacked architecture to achieve HDR imaging in accordance with the teachings of the present invention.

#Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.

#In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one having ordinary skill in the art that the specific detail need not be employed to practice the present invention. In other instances, well-known materials or methods have not been described in detail in order to avoid obscuring the present invention.

#Reference throughout this specification to “one embodiment”, “an embodiment”, “one example” or “an example” means that a particular feature, structure or characteristic described in connection with the embodiment or example is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment”, “in an embodiment”, “one example” or “an example” in various places throughout this specification are not necessarily all referring to the same embodiment or example. Furthermore, the particular features, structures or characteristics may be combined in any suitable combinations and/or subcombinations in one or more embodiments or examples. Particular features, structures or characteristics may be included in an integrated circuit, an electronic circuit, a combinational logic circuit, or other suitable components that provide the described functionality. In addition, it is appreciated that the figures provided herewith are for explanation purposes to persons ordinarily skilled in the art and that the drawings are not necessarily drawn to scale.