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It Starts with
the Pixels
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The fundamental nature of image systems favors a
large sensor array in order to collect more light, resulting in image reproductions
that captures a high level of detail. However, in image applications
today, the physical size of the camera module is tightly constrained
requiring small pixel sensors. For example, in order to use 1/4”
optics for slim profile camera phones, a 2.2µm pixel size is required for
2 Megapixel resolution and a 1.75µm pixel size is required for 3
Megapixel resolution. At these pixel sizes and resolutions, the sensor
must be able to balance several design elements to obtain the highest
sensitivity and dynamic range.
The challenges of small pixel applications have led
to innovations in CMOS image sensor design that continue push the
boundary of image quality performance. The adoption of 4-transistor (4T) pixel
design have significantly improved dark current and reset noise
performance. However, to maintain the highest level of sensitivity, care
must be taken to minimize noise and parasitic capacitance from the
photodiode and read out circuit. For small pixels, read noise is one of
the key limiting factors for low-light sensitivity requiring low noise
designs (for large pixels the limiting factor is photon shot noise) . The
entire pixel readout process is also performed at a high rate in order to
minimize the artifacts and motion blur of the image. This is especially
important for higher speed video quality. If all of these design elements
are done right, minimal digital compensation is required, resulting in
accurate reproduction that is true-to-life.
To meet the challenges of small pixel design,
Himax Imaging is developing a series of sensor products based on a new
generation of proprietary designs. With proven experience in designing
CMOS image sensors and SoC solutions for high volume imaging applications,
Himax Imaging utilizes the latest technology in CIS process, optics
modeling, mixed-signal design and image processing to deliver the right
size, power, cost and convenience required for high resolution sensors in
extremely small form factor. Himax Imaging sensors are highly
integrated to minimize system cost and space for a wide variety of
applications.
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