Logic on Board - Carl Hanser Verlag

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SPECIAL: MACHINE VISION
CMOS Sensors
Logic on Board
CUSTOM CMOS IMAGE SENSOR SOLUTIONS
SERVING THE CHALLENGE OF DEMANDING APPLICATIONS
CMOS image sensors enter new applications many of which are traditional CCD domains. Since
the CMOS chip may host additional logic, completely new markets arise – such as holographic
memories and disposable endoscopes.
JOOST SEIJNAEVE
lenges such as device testing and device
sensitivity. Currently, the smallest CMOS
image sensor produced by Cypress measures just 1 mm x 1 mm. Soon its size will
drop to 0.5 mm x 0.5 mm. No wonder that
these incredible small packages are real
challenges in the development of new
testing methods.
This article is to discuss both applications, data storage and endoscopy, in de-
tail and to point out the requirements and
benefits of advanced CMOS image sensors.
MOS image sensors already replace
CCDs in many of their traditional apCustom CMOS image sensors
plications. Additionally, new marfor holographic storage
kets for CMOS sensors emerge. Interesting
price points are not the only reason: CMOS
Optical storage devices record and hold
sensors and additional logic circuitry may
data only in the surface of a medium. To
be integrated on the same silicon die. The
increase data storage capacity, holoholographic storage market is an example
graphic techniques can be used which
of a brand new application area
where CMOS image sensors are required to realize total solutions for
demanding applications.
In any data storage application,
it is of utmost importance to have
an image sensor delivering high
resolution, sensitivity, frame rate
and a significant feasibility of integration with logic. Cypress, in a
dedicated collaboration with Inphase, has developed a 3-Megapixel CMOS image sensor to operate at 500 frames per second, appropriate for on-chip ADCs and
LVDS.
A disposable endoscope is a
good example to demonstrate that
CMOS sensors can replace traditional CCD sensor types. On-chip
integration, miniaturization and
1 To form a holographic image in a recording medium, light from a single laser beam is split into a signal
packaging are all equally imporbeam, carrying the data, and a reference beam. At the point where these two beams intersect with the
tant for this application. However,
recording medium, a hologram is formed. To read out these data at high speed, the reconstructed array is prominiaturization raises new chaljected onto a CMOS image sensor
© 2007 Carl Hanser Verlag, Munich, Germany
www.laser-photonik.de
C
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© 2007 Carl Hanser Verlag, Munich, Germany
www.laser-photonik.de
Not for use in internet or intranet sites. Not for electronic distribution.
CMOS Sensors
2 The architecture of a highspeed image
sensor for
endoscopy
record data on multiple levels within the
media. Holographic techniques allow millions of bits of data be written or read in
parallel. This enables transfer rates significantly higher than with current optical
storage devices.
Figure 1 shows the basic principle of
holographic storage. Light from a laser
beam is split into a signal beam carrying
the data, and a reference beam defining
the depth at which the data is stored onto
the media. At the point where the two
beams intersect the recording media, a
hologram is formed. To encode digital
data onto the signal beam, a spatial light
modulator (SLM) translates them into an
optical checkerboard pattern of light and
dark pixels. This data pattern is arranged
into an array or page containing millions
of bits. The amount of data possible to
store depends on the spatial resolution reliably available. To read out the data, a
reference beam is deflected from the hologram in the storage media to reconstruct
the stored information. This hologram is
then projected onto a CMOS image sensor
that can read the data in parallel.
To its detriment, the development of
holographic data storage products up to
now has been limited by the lack of lowcost system components and by the complexity of holographic multiplexing tech-
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niques. Another drawback has been the
absence of suitable recording materials.
Recently, however, an innovative firm by
the name of Inphase has succeeded in
solving these issues. As far as the image
sensor goes, only a custom designed CMOS
image sensor will enable a practical solution. To read out the huge amounts of
holographically stored data as fast as possible, and at an appropriate quality, a
high-resolution CMOS image sensor with a
high frame rate is required.
CONTAC T
Cypress Semiconductor
Corporation Belgium BvBa,
B-2800 Mechelen,
Tel. +32 (0) 15 /44 63 -43,
Fax +32 (0) 15 /44 63 -44,
www.cypress.com
Vision: Hall 4/Booth C55
For this typical storage application, Cypress has developed a CMOS image sensor
with 3 Megapixels, operating at about 500
frames per second. In this configuration,
the readout speed of the holographic data
reaches up to 1.5 Gigapixels per second,
whereas each pixel represents 1 bit of the
holographic data. Additionally, high sen-
SPECIAL: MACHINE VISION
sor sensitivity is needed as the reference
beam is limited in light power and integration time is short due to the fast readout speed.
Low-light operation conditions require
high sensitivity and high pixel quality.
Consequently, at the sensor level, 8-bit
ADCs are foreseen in combination with
pre-amplifiers to guarantee that the quantization noise is sufficiently below signal
level. Therefore, the data stream delivered
by the sensor amounts to 1.5 Gpixels/s, at
8 bits/pixel or 12 Gbit/s.
This huge amount of data coming out
of the CMOS image sensor is split over 32
LVDS channels, each working with 400
Mbit/sec. The LVDS interfaces can be directly connected with the LVDS inputs of
a Xilinx FPGA. This allows a very compact
and power-efficient design of the complete read-out system. Power dissipation
of the sensor is very critical due to the
compact setup of the whole holographic
storage module. The sensor has been optimized for low power dissipation - with
no more than 1.1 W.
Figure 2 shows the architecture of the
high-speed image sensor used for holographic data storage.
Taking the above specifications into account, only a custom CMOS image sensor
can yield a good solution for this application. Additionally, it is important to provide a complete turn-key solution. This
means the BGA package and the glass lid
with special coating both are custom
made as well. The production of this sensor in higher volumes, with specific quality requirements, is part of the custom
service.
CMOS image sensors
for endoscopes
CMOS image sensors are set to invade the
application areas traditionally reserved
for CCDs. At a comparable image quality
and easier to use, they are cheaper and
they offer the integration of additional
functionality on the same silicon chip. As
a consequence, they now open up the design of cost-efficient and robust disposable endoscopes. One-time use avoids the
rather complicated sterilization procedures and eliminates the risks of infection.
Endoscopes are well known and have
been used for a significant time. Besides
their medical applications, they have V
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CMOS Sensors
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3 Disposable endoscope: Micro Imaging’s new
concept helps overcome sterilization problems
(left); optics and image sensor are placed inside
the tip of the device (bottom)
© 2007 Carl Hanser Verlag, Munich, Germany
www.laser-photonik.de
also found numerous technical applications such as in the quality assurance of
systems, in preventive maintenance, and
many more. Generally, they are used as advanced tools in the visual examination of
difficult to reach cavities.
The broadest application area of endoscopes, however, still is in the medical
professions. Through natural orifices of
the body or by small surgery, the tip of an
endoscope is brought into the body for examination purposes. Some endoscopes
work with glass lenses integrated in their
tips by transferring the image through the
lens to the CCD image sensor outside the
body. Such systems are also called video
endoscopes.
Placing the sensor module outside the
body makes sterilization much less complicated, despite the fact that the whole setup
is still expensive as the tip with its highly
accurate lenses needs to be sterilized anyway. Additionally, there is a significant loss
in image quality because image transfer
through the lens is extremely difficult. But
a traditional video endoscope has three significant disadvantages: lack of image quality, need of sterilization and high manufacturing and maintenance cost.
To overcome these problems, a custom
made CMOS sensor is considered. Microimaging Solutions solves the problems of
image quality, sterilization and cost
through a novel approach. This is done by
placing the image sensor inside the tip of
the scope. This enables the endoscopes to
be delivered fully sterilized and stored locally for application. The advantage is the
elimination of sterilization and reconditioning costs. This results in significant
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4 Recent CMOS image sensors may offer an
extremely small footprint and contain additional on-chip circuitry
savings in material and personnel.
For medical applications, since the endoscope tip will go inside the body, the tip
should be as small as possible. This imposes a significant challenge on sensor
configuration. As the size of the sensor
must go down, resolution, image quality
and sensitivity all must go up. Additionally, driving the sensor and interfacing it
to the outside world, as well as its power
dissipation all should be at a minimum
level. As a consequence, scalability of the
CMOS technology employed is required.
Currently produced sensors come in sizes
of 1 mm x 1 mm. Soon there will be ones
measuring 0.5 mm x 0.5 mm.
In contrast to the CCD image sensors
currently used, CMOS image sensors are
easier and cheaper to manufacture on existing CMOS lines. In a high-volume production, such a component should be
available at less than $10. This in turn
drops the cost of a disposable endoscope
to below $200.
Another significant advantage of CMOS
is the feasibility of integrating additional
standard logic circuitry on the image sensor chip, such as drivers, converters,
logic, etc. Due to the high integration
density this yields very compact devices.
Also of advantage is that CMOS circuits
appear to be less sensitive to the magnetic fields generated by medical RF
equipment. Thus, CMOS needs less shielding and a single supply voltage of 2.5 V is
sufficient for their operation. This simplifies endoscope design.
The entire concept of a CMOS image
sensor, however, would fail if it could not
be combined with the use of an extremely
small package. A shellcase package is no
larger than the silicon die itself and is
perfectly suited for this application. The
small package and the small form factor of
the image sensor for endoscopes together
5 | 2007
© 2007 Carl Hanser Verlag, Munich, Germany
www.laser-photonik.de
Not for use in internet or intranet sites. Not for electronic distribution.
CMOS Sensors
SPECIAL: MACHINE VISION
need a careful consideration of how much
additional functionality should be realized, as this determines the number of
connections to the outside world. The minimum are four connections: mass, supply
and two counter-phase outputs.
CMOS image sensors as developed by
Cypress to accommodate disposable endoscopes provide a resolution of 100 x 100
up to 1150 x 1150 pixels, equaling 1.3
Mpixels. Pixel sizes can go from 6 mm
down to 2.5 mm and frame rates are between 30 to 60 frames per second. Power
consumption varies between 20 and 99
mW. Read noise is as low as 18e-. Color reconstruction is done by Bayer pattern.
As the concept of a disposable endoscope demonstrates, Cypress designs and
manufactures CMOS image sensors that
can be specifically matched to the requirements of the customer's application.
Where CCD was common technology in
endoscopes, the novel approach using
CMOS image sensors will open up this market by replacing CCDs.
Summary
Holographic storage and disposable
endoscopes are only two innovative
examples of what CMOS image sensors
can do these days. Customers are now in
a position to endow their products with
unique features through applicationspecific image sensors to differentiate
them from the competition and open up
new market opportunities.
CMOS image sensors will not only replace CCDs in existing markets. CMOS
allows a different approach to these
markets. CMOS sensors open up new
markets as well since they now can fulfill their technical and commercial
aspects. ■
AUTHOR
JOOST SEIJNAEVE is Director of Business Development
Custom CMOS Image Sensors with Cypress Semiconductor
in Mechelen, Belgium.
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