ON Semiconductor has announced
their latest CCD image sensor, the KAI-50140, that incorporates 50
megapixels with industrial inspection in mind.
One feature in particular about this image sensor that makes it useful for AOI (automatic optical inspection) is that the aspect ratio of the CCD is 2.18:1. This is a common ratio of smartphone displays making it possible for this sensor to image a smartphone with 50MP of data and little wasting of image pixels. The resulting high-resolution images allows for even the tiniest details to be detected by the CCD when used in AOI applications improving failure detection rates and therefore reducing costs to any production line.
The KAI 50140 sensor (left) and graphic of its dimensions (right). Images used courtesy of ON Semiconductor.
Each pixel on the CCD sensor has the capacity to hold up to 13,000 electrons and with up to four outputs on the sensor the CCD can produce up to 4 frames per second (which would potentially correspond to 4 optical checks per second when used in AOI). Housed in a 72 pin PGA, the CCD has 10440 x 4800 active pixels with a 40-pixel width border around the active area which can be used for dark sensing (adjusting for zero light).
Block diagram of the KAI-50140. Image used courtesy of ON Semiconductor
This is the latest in the KAI family. In March, ON Semiconductor had released the KAI-43140, a 43.1 MP CCD sensor designed for AOI and surveillance.
CCD Sensors vs CMOS Sensors
CCD sensors (charge-coupled device) and CMOS sensors are both image technologies that allow the capture of images but are fundamentally different.CMOS Sensors
CMOS sensors use active pixels, which involve a photosensitive area (such as a photodiode) and an amplifier which converts the received photons into an electrical signal. This signal is then amplified and then read by analog circuitry to be converted into digital circuitry.Multiple pixels in a CMOS image sensor can be read at once using parallel busses. This allows for high frame rates (such as 60fps) at relatively low costs, which is why CMOS sensors are the predominant form of imaging technology for commercial cameras (such as smartphones and handheld camcorders) in the market.
CCD Sensors
A CCD operates by transporting charge instead of electrical current. Pixel sensors on a CCD are passive and each pixel converts incoming photons into electrical charge (a build-up of electrons inside a well). These electrical charges are trapped inside small wells and, due to the nature of the silicon construction, the quantum efficiency is close to 95%, which means that the charge very closely represents the exact number of photons that hit the sensor.This method for reading pixels also results in far less noise than converting each pixel into an electrical signal. These charges, instead of being converted into electrical signals, are transported through the silicon by enabling gates which effectively mimic a shift register. At the end of the charge shift register, a charge amplifier converts the charge into an electrical signal which is the pixel output.
Unlike CMOS sensors, CCDs are read pixel by pixel which can make them significantly slower (when comparing like for like), but the image quality is often far superior.
A gif demonstrating charge transfer. Image created by Michael Schmid [CC-BY 2.5]
CMOS and CCD Applications
When it comes to the applications of CCDs and CMOS sensors, a CCD will often be used in scientific and industrial scenarios where high-resolution, high-quality images are required but not necessarily at high frame rates (such as astrophotography). This would be useful in situations involving machine learning and (AOI) where a computer can quickly photograph a PCB or completed circuit and check for defects including poor solder adhesion, incorrect component placement, and damaged PCBs.CMOS sensors are more suited for situations involving video and photography where quality is not entirely important and costs need to be kept down. However, that is not to say that CMOS sensors are bad; CMOS sensors can be incredible and are totally acceptable by consumer standards producing stunning photographs and video.
2018's CMOS Sensors So Far
The KAI-5014 CCD is not the only sensor to be announced this year and while the KAI-5014 boasts high-quality images at a specific ratio of 2:1 other sensors on the market may be potential contenders.ams CMV50000 (CMOS)
The ams CMV50000 is a 47.5 megapixels CMOS sensor. It has an effective image size of 7920 x 6004, which is less than what the KAI CCD can provide—but, unlike the KAI CCD, the CMV50000 can be used at a frame rate of up to 30fps. This makes the CMV50000 particularly useful in applications including machine vision, video and broadcast, security, high-end inspection, document scanning, and even 3D imaging.The CMV50000 has a ratio of 1.31:1 (far less than the 2.18:1 of the KAI-5014) which may make it less practical for AOI in smartphone production.
The CMV50000. Image used courtesy of ams.
The CMV50000's low noise and high sensitivity capabilities make it suitable for low-light conditions. Additionally, it has a dual exposure HDR mode which allows the combination of a low exposure and high exposure image to produce an image that dims bright areas and brightens dim areas.
ON Semiconductor AR0221 (CMOS)
The AR0221 is an ON Semi 1/1.7 inch CMOS sensor that has an active pixel array of 1928 by 1088 pixels and contains 2.1MP.
The ARO221. Image used courtesy of ON Semiconductor
Capable of capturing video at 60fps, the AR0221 is intended for applications involving video surveillance, high dynamic range, body cameras, action cameras, and even car DVRs. Designed to output 1080p video, the sensor has notable low light performance, auto-black level calibration, back-side illuminated pixel technology, integrated color correction, and lens shading correction.
Unlike the KAI CCD, the AR0221 is specifically for commercial applications where the footage quality is not entirely important but a high FPS is needed (the KAI-50140 CCD is 4fps whereas this sensor is 60fps). While this sensor only has 2.1MP—significantly fewer than the number found in the CCD—it is still able to produce 1080p footage and has inbuilt auto-corrections.
Canon (CMOS)
One final sensor to mention is certainly not available for commercial use. In July, Canon announced a comparatively gigantic CMOS image sensor—20cm on each side. This sensor is clearly intended for applications that are far different from the others listed here. In fact, this massive sensor is suitable for a much grander scale of applications, including possibly defending the earth from meteors.Smaller, faster CMOS sensors that can record high-speed video will continue to gain popularity as slow motion and 4K video become more standard in consumer applications. High megapixel count CCDs will also likely see increased integration into industrial processes as automation becomes more prevalent.
What other image sensors have been caught your eye in 2018? Share your thoughts in the comments below.
Featured image used courtesy of ON Semiconductor.
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