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While light sensitivity is an important
specification for all image sensors,
some applications require devices
that are capable of operating
under very low lighting conditions,
beyond the range where standard
image sensors are useful. Whether
detecting a fluorescent marker
viewed under a microscope, an
image of the retina captured with
an ophthalmic fundus camera, or
a surveillance image operating
on a cloudless, moonless night,
technologies that enable very low
light imaging – enabling 30 fps
image capture at illuminations down
to 0.1 lux – can be critical to success.
Historically, Electron Multiplication
Charge Couple Device (EMCCD)
technology has been very successful
Interline Transfer EMCCD Technology Enables a New
Regime of Very Low Light Imaging
Michael DeLuca, Go to Market Manager, Industrial and Security Division,
Image Sensor Group, ON Semiconductor
the Full Frame Transfer technology
traditionally used for EMCCD designs
limits the resolution available from
these devices to approximately
one megapixel or lower, restricting
the spatial image quality available
when using this technology in video
applications.
Interline Transfer EMCCD technology
addresses
these
limitations
directly by combining the low light
sensitivity available from an electron
multiplication output register with
the image uniformity, resolution
scaling, and electronic global shutter
capabilities of Interline Transfer
CCD. This combination enables
the development of image sensors
that can capture continuously from
very low light to bright light in
in enabling the capture of scenes
with very low light levels. This
technology takes the very small
charge detected in a pixel under
low light and multiplies it many
times before reaching the sensor’s
amplifier, allowing the initially
unresolvable low signal level to be
raised above the amplifier noise
floor for detection. While this
technology excels at image capture
under low light levels – even down
to the detection of single photons –
the electron multiplication cascade
can overflow and create blooming
artifacts if signal levels entering the
EMCCD register are too high, limiting
use of sensors with this technology
to scenes that do not contain any
bright components. In addition,
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