Common counter input
Column level amplifers and ADCs
slope 11 bit ADC
March 2014 VISION SYSTEMS DESIGN www.vision-systems.com 8
sCMOS cameras target
Andrew Wilson, Editor
While general purpose CCD and CMOS
imagers are used in many off-the-shelf digital cameras, novel imager architectures are
needed to address the needs of more specialized markets. In scientific imaging, for example, cameras must exhibit high-resolution,
fast frame rates, and high-sensitivity.
Recognizing this, in 2008, a consortium of
companies consisting of Andor (Belfast, Ireland; www.andor.com), Fairchild Imaging
(Milpitas, CA, USA: www.fairchildimaging.
com) and PCO (Kelheim, Germany; www.
pco.de) embarked on a collaborative development to develop a CMOS-based architecture to meet these criteria. An imager based
on the resultant technology, known as scientific CMOS (sCMOS) was introduced as a
prototype one year later. Featuring a 2560 x
2160 format 6. 5 x 6. 5 μm pixels, the imager
featured a dynamic range of 14-bits at 30 fps
and a read out noise of less than t wo electrons
at this speed ( http://bit.ly/1hjdsp W).
To attain this dynamic range and read
out noise, the sensor features a split readout
scheme of odd and even columns. As each
pixel from each photo-site is read out, dual
amplifiers and analog to digital converters
with independent gain settings are applied
to the signal and combined to achieve a high
dynamic gain (Figure 1).
The design of such a sensor was first presented by Paul Vu and his colleagues at
Fairchild Imaging in June 1988 (http://bit.
ly/1dvMGGG). Today, the company offers
image sensors based on variations of this technology that consist of the CIS1910F, a 1920 x
1080, 100fps device that features an array of
5T pixels on a 6.5µm pitch and the CIS2521F,
a 2560 x 2160 device with 6.5µm pitch pixels.
Both sensors support both rolling and global
shutter modes of operation. Which mode of
operation is chosen will be application dependent. In many machine vision applications,
for example, where products must be imaged
as they travel along a production line, motion
blur can be eliminated by using a global shutter. In scientific applications, where the frame
rate of the camera can compensate for any
potential motion of the sample, a rolling shutter may be used. Many of the currently available sCMOS-based cameras available today
support both modes of operation (Table 1).
To support the high data rates produced
by these cameras, many incorporate the well-
established CameraLink interface. Recently,
however, the emergence of USB 3 has led
some vendors to introduce cameras that incor-
porate this interface. While not as fast as the
CameraLink interface, incorporating the USB
3 interface reduces the cost of an imaging
system since no frame grabber is required as
the USB 3.0 interface is now commonplace on
PC-based systems. At the same, time, however,
the slower USB speed leads to a lower readout
rate from the camera, a limitation that may not
be important in scientific applications.
In the past, such applications required Elec-
tron-Multiplication Charge Coupled Device
(EMCCD)-based cameras to provide the low
read out noise, high dynamic range and high-
Figure 1: In the design of Fairchild’s sCMOS imagers, dual amplifiers and analog to digital
converters with independent gain settings are applied to the signal and combined to achieve
a high dynamic gain.