Harvest Imaging Blog

Yesterday morning (Sep. 21st, 2016) I attended a few sessions of AutoSens 2016 in Brussels.  It is a new conference organized by the people who started and grew Image Sensors Auto at the time they were still working for Smithers.  AutoSens was very well attended and was very well organized in a great setting, namely in the Auto-Museum in Brussels.  Excellent choice !

In the morning sessions, there were 3 papers related to image sensors.  Pierre Cambou (YOLE Development) talked about new developments in mobile and their spin-off to automotive applications, Daniel van Nieuwenhove (Softkinetic) gave a nice overview of 3D imaging technologies and how the Softkinetic’s solutions fit into this landscape, and Tarek Lule’s (ST) presentation was about a HDR flicker-free CMOS image sensor.  The latter one had the most technical information, although Tarek did not give any details about the pixel architecture.  But what I understood from his talk is the following : the pixels are making use of multiple photodiodes :

• a large photodiode is capturing information in an continuous mode during the exposure time, with a high sensitivity and is basically “looking” after details in the darkest parts of the image,
• a small photodiode that is capturing information in a chopped mode : during the exposure time the photodiode is active during short periods of time and is inactive during the remaining time of the chopping period, it sums the signals obtained during these short periods of time.  In this way, information is collected AT THE SAME TIME as the large photodiode, but because of the size and of the chopping, the diode “looks” after details in the mid-range of the image, motion artefacts can be avoided,
• a small photodiode that is capturing information in a chopped mode : during the exposure time the photodiode is active during VERY short periods of time and is inactive during most of the time of the chopping period, and it sums the signals obtained during these very short periods of time.  In this way, information is collected AT THE SAME TIME as the large photodiode, but because of the size and the chopping, the diode “looks” after details in the high-range of the image, motion artefacts can be avoided.  The chopping frequencies for the two smaller diodes is the same, the only difference is the duty cycle of active and non-active.

Apparently the pixel needs three photodiodes, but because of the chopping, the work that needs to be done by the two smaller photodiodes can be done by a single one in combination with an appropriate time-multiplexing between the short and very short active times within the chopping period.  So, the pixel is based on two photodiodes in combination with a few storage nodes.  More information was not revealed …

Conclusion : clever idea to make a flicker-free imager with a high-dynamic range (quoted 145 dB).  Not many performance numbers were given, but the overall working of the device was shown by means of a video.  Looking forward to learn more about this device !

Albert, 22-09-2016.

Most probably several readers of this blog were not yet born in September 1976, but exactly 40 years ago I started my career in solid-state imaging.  Of course I could never ever have guessed that 40 years later I would be still involved in the same discipline.

When I was facing the start of my last year of the MSc-EE studies (at the Catholic University of Leuven, Belgium) in September 1976, I had to choose a MSc thesis subject.  Purely by coincidence I found an MSc thesis project in the team of Gilbert Declerck and under the daily guidance of Jan van der Spiegel, being a PhD candidate in the CCD group.  The topic was based on the development of the hardware around a bi-linear CCD of 256 elements.  The digital driving pulses as well as the analog signal processing needed to be designed and needed to be built on a breadboard.  The CCD needed to be synchronized to a rotating drum, just to show the principle and capabilities of the imaging device.  At that moment, 40 years ago, a bi-linear device of 256 elements was already something special.

I remember that another PhD candidate, being Peter Schreurs, explained to me the basic principles of a CCD.  I still can recall in which lab space it was.  It was Jan van der Spiegel who explained to me the technology of the CCDs and showed me how he made the design and lay-out of the devices.  At that time, CCD image sensors were designed and fabricated in the clean room of the ESAT laboratory (Electonics, Systems, Automation, Technology).  The environment and the atmosphere in the basement of the EE-building was a great stimulation in the learning process in the field of the “young” semiconductor technology.  During the 9 months of the MSc thesis project, and especially for the hardware part of the task, I worked very closely together with Tony van Nuland.  He thought me the practical ins and outs of digital and analog circuitry.  Afterwards seen, this was the very basic start of a long and lasting career in solid-state imaging.

Gilbert Declerck, the promotor of my MSc thesis, became later the CEO of IMEC; Jan van der Spiegel, my daily supervisor became professor at Penn State University in Philadephia (USA); Peter Schreurs who explained to me the working principles of CCDs started a career at Agfa and Tony van Nuland who helped me with the hardware became a specialist in the field of ion implantation and focused-ion beam techniques at the university’s ESAT laboratory.  As you can judge, I was in good company !  Thanks to all of you !

Albert, 22-09-2016.