Field of the Disclosure
The present invention relates generally to imaging, and more specifically, the present invention is directed to high dynamic range image sensors.
Background
Image sensors have become ubiquitous. They are widely used in digital cameras, cellular phones, security cameras, as well as, medical, automobile, and other applications. The technology used to manufacture image sensors, such as for example complementary metal-oxide-semiconductor (CMOS) image sensors (CIS), has continued to advance at a great pace. For example, the demands for higher resolution and lower power consumption have encouraged the further miniaturization and integration of these image sensors.
High dynamic range (HDR) image sensors have become useful for many applications. In general, ordinary image sensors, including for example charge coupled device (CCD) and CMOS image sensors, have a dynamic range of approximately 70 dB dynamic range. In comparison, the human eye has a dynamic range of up to approximately 100 dB. There are a variety of situations in which an image sensor having an increased dynamic range is beneficial. For example, image sensors having a dynamic range of 100 dB or more are sometimes needed in the automotive industry in order to be able to handle different extreme lighting conditions, such as driving from a dark tunnel into bright sunlight. Another extreme lighting situation example occurs when imaging light emitting diode (LED) illuminated vehicle lights, traffic lights, and signs that are pulsed at for example 90-300 Hz with high peak light intensity. In these LED lighting situations, there is often flickering present in the output images caused by the LED light sources, which can result in unreliable or inaccurate image sensing.
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.