Harvest Imaging Blog

This blog started about one month ago and the main purpose is to share information and/or to stimulate discussion in the field of solid-state imaging.  After two general topic stories, I will soon start with items having more technical content, for example, the various noise sources in image sensors.  This plan of introducing more technical items does not imply that every future article published in this blog will have technical or scientific information.  Depending on my inspiration I will publish also non-technical stuff in between.

 A while ago I started working on a new course program : a two-day or three-day course with hands-on measurements on existing, off-the-shelf solid-state cameras.  The basic idea for this new course is to use the photon-transfer curve to do the evaluation of a sensor/camera.  The photon-transfer curve (also called “mean-variance method” or “photon-shot noise method”) was published for the first time in the 80’s by Jim Janesick (those days working at JPL).  Long time ago I had a discussion with Jim about his measurement technique.  He told me that he discovered more and new benefits of the photon-transfer curve (PTC) each time he worked on it.  To my own surprise I have to admit that Jim was right.  The PTC is a great evaluation tool, because basically you do not need to know what is inside the sensor/camera under test, and absolute light measurements are not needed.  All together, the PTC method is an easy way to get a lot of information (performance parameters and characteristics) about the sensor/camera under test.

During the preparation of the new course material I developed a noise model for a 4T CMOS image sensor.  The model describes the fixed-pattern noise as well as the temporal noise present in rolling-shutter pinned-photodiode pixels (PPD).  Next to the PPD, the imager is provided with column-level CDS, a global output amplifier and an on-chip analog-to-digital converter.  The model takes into account also the noise generated by these peripheral circuits.  By using this noise model I do have the possibility to change every single noise source in the hypothetical CMOS imager and to study its effect on the PTC. 

In the near future I will share this information with you through this blog.  In the very first publication I will focus on the dark current shot noise and its effect on the PTC.  The “P” of the PTC stands for “photon”, but the basic PTC idea can be successfully applied to the dark current present in the imagers and its shot noise component as well.  In other words, in the coming weeks I will describe how to apply the photon transfer curve without a single photon coming to the imager. 

Albert 2009-08-06

1969, a year to remember or not ? I think that 1969 was a great year, a year to remember, at least for me !  Let me tell you why.

 At that time I was 15 years old, living in Belgium and enjoying cycling very much, at least in a passive way by watching cycling sports on TV.  What happened on July 20^th 1969 ?  Of course, Neil Armstrong was the first man on the moon.  Everybody knows, but basically on the same day, Eddy Merckx – elected to be the Belgian sportsman of the 20^th century – won his first (of five) Tour de France.  In Belgium the newspapers did not know what to put on the front page : Merckx or Armstrong.  Both men were writing history, at least in our tiny small country.  One newspaper came with a unique solution : they printed a newspaper with two front pages, back-to-back.

But more happened in 1969 : in the beginning of that year, a new type of airplane made his first flight, the jumbo-jet Boeing 747.  Over the last 40 years many improvements were introduced to the 747, but basically what we have today is still the same concept as 4 decades ago.  Every time I fly to the USA or to the Far East in a 747, this flying “monster” impresses me again and again : so big, so huge, so heavy, and after 1 minute on the runway it takes off.  Amazing that the 747 survived 40 years.

Keeping in mind the name of my company, another major milestone was set in 1969 : Woodstock.  People of my age probably remember the very first big, open-air rock-‘n-roll festivals.  And Woodstock was one of the biggest ever organized.  Very famous was the set by Jimi Hendrix playing the Star Spangled Banner on his guitar with his mouth.  But there was a “super” group announced having David Crosby, Stephen Stills and Graham Nash being the front men.  During their show at Woodstock, another “hero” totally unexpected joined them on stage : Neil Young.  That is how I got to know his music and more, that is how I got addicted to it.

Merckx, Armstrong, 747, Woodstock, Neil Young, all big names that made a great impression on me.  But also in 1969 two young engineers from Philips Research in Eindhoven (Netherlands) were working –  already during a couple of years – on a new solid-stated device.  They called it a Bucket-Brigade Device (BBD) and they published their first results in the famous year 1969.  The two researches, Leo Sangster and Kees Teer, announced their new device being an analog memory.  But in their original publication, they also mentioned the potential of the device to act as a solid-state image sensor.  Soon after the introduction of the BBD, it was recognized that the BBD had too many disadvantages to become a commercial success, but ultimately it formed the basis for the Charge-Coupled Devices (CCD, published in 1970 by Boyle and Smith of Bell Labs).  A few years later, in 1976, I started working on CCDs.  At that moment I could not realize that the technical and scientific work published in 1969 almost completely determined my professional career.  

Maybe some of the things that happened in 1969 sound like details to you, but some of them are really milestones to me !  1969 is an important year to remember.  Wasn’t it the Summer of ’69 Bryan ?

Albert 2009-07-23

From June 25th till June 28th 2009, the International Image Sensor Workshop 2009 took place in Bergen, Norway (see also www.imagesensors.org).  I had the honor to be the General Chair of this event.  Since the first workshop in 1986, organized by Eric Fossum, the workshop has considerably grown, and its organization can no longer be done by a single person.  I was lucky to get assistance from Chantal Castelijns (DALSA), the secretary of the workshop, and Johannes Solhusvik (Aptina), the technical program chair.

Within the imaging community, the workshop is recognized as the world’s most important gathering of technical image-sensor people.  Can you imagine : without any technical program available and without indicating the exact location of the workshop, the workshop was completely sold out only 3 days after the start of the registration.  This clearly demonstrates the importance of the workshop.  About 2/3 of the participants attended already an earlier workshop, about 1/3 of the participants attended for the first time.  Remarkably was the high number of European participants and the low number of attendees coming from North America.  This clearly was a result of the economic downturn. 

During the workshop I got many times the following questions :

–          Why limiting the number of participants to 140 people ?  The reason to limit the audience has to do with the more open atmosphere that can be created amongst a smaller group of people, to stimulate the discussion during the technical meetings as well as the informal contacts during the breaks,

–          Why using a hotel in the middle-of-nowhere ?  Basically for the same reason, trying to keep the group together, also in the evening hours when it is time for social networking,

–          Why going to an expensive country such as Norway ? Because the days are so long in Norway (especially around June 21^st).  From previous workshops it was learned that the technical program during the day was quite heavy.  So we thought of making it easier to absorb by extending the length of the days 😉

The workshop tried to bring innovation in its own product as well : for that reason the workshop was extended with an extra day, actually an extra opening day was added and assigned to a “hot imaging technology”.  What kind of imaging subject these days is hot ?  We thought that the hottest technology at this moment is Back-Side Illumination (BSI).  Although the technology by itself is not new, BSI for CMOS consumer devices is.  About one year ago the very first announcements of BSI-modules were made, and since then everyone is eagerly looking forward to see images of these technical miracles. 

The workshop organization invited 7 world-experts in the field of BSI to give each a presentation of 1 hour.  In this way an outstanding and appealing program was put together.  The extra BSI opening day was extremely well received by the participants.  Although it is not yet decided, it looks more than logical to continue with this initiative of opening the workshop with an extra day devoted to one specific subject.

Looking forward to IISW2011 when Nobukazu Teranishi is going to host the workshop,

Albert 2009-07-14