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Wednesday, February 25, 2009

CCD sensors boost frame rates

CCD sensors boost frame rates

By Ann R. Thryft, Contributing Technical Editor -- Test & Measurement World, 2/1/2009

Marketing manager
Eastman Kodak, Image Sensor Solutions

Progressive-scan cameras used in semiconductor and electronics inspection produce images of objects moving down an assembly line by imaging an entire object in one shot, a process that generates high-quality images but tends to create manufacturing bottlenecks. As engineers demand faster camera frame rates to speed up production line throughput, manufacturers of progressive-scan cameras are designing new sensors to improve camera performance. Michael J. DeLuca, marketing manager for Eastman Kodak's Image Sensor Solutions group, discussed how newly designed progressive-scan CCD image sensors can boost frame rates and image quality while lowering system costs.

Q: What are engineers looking for in progressive-scan cameras?

A: In semiconductor and electronics inspection, there's always a need for faster frame rates and higher resolution. Users also want greater sensitivity (meaning the ability to get clear images at low light levels) as well as reduced costs. On top of all this, cameras need to match standard optical formats, such as 1/2 in. and 2/3 in., since this increases compatibility with a wide range of lenses.

There is also a trend toward smaller lenses, since they weigh less, cost less, and take up less space than bigger lenses.

Q: How can image sensors help improve camera performance?

A: You can improve imaging performance by reducing pixel size to get more pixels in the same area. For example, one of the new sensors in our Interline CCD family, the KAI-02050, is a 2-Mpixel, 1600x1200 device in a 2/3-in. optical format. Because it is based on a 5.5-micron pixel, about half the size of our previous-generation 7.4-micron pixel, the sensor contains twice the number of pixels in the same optical format as before.

Alternatively, you can get the same number of pixels in a smaller optical format, which helps reduce camera size and allows the use of smaller and less expensive optics. For example, another member of this family, the KAI-01050, fits 1 Mpixel in a 1/2-in. optical format, instead of the 2/3-in. size necessary for the previous-generation 1-Mpixel sensor.

We also increased the potential frame rate of all the sensors in this family by doubling the number of outputs, which helps improve system throughput. The KAI-02050, for example, operates at a maximum 68 fps, compared to 35 fps in the previous-generation 2-Mpixel sensor.

Q: What else can be done to improve progressive-scan cameras?

A: Camera makers also want the ability to leverage camera electronics across multiple models to help reduce cost. This can be achieved by basing several sensors on the same design platform, using the same ceramic package that contains the sensor chip, and using the same electrical pin definitions, making them all plug compatible. This is true of the sensors in this family. Because the sensors operate the same way, it's easy for camera manufacturers to leverage an existing design when a new sensor becomes available, bringing a new camera and its new sensor technology to market faster.

In addition, since smaller pixels can't collect as much light as bigger pixels, they aren't usually as sensitive under low-light conditions. In moving to this new technology platform, however, we made sure that key imaging parameters like sensitivity and dynamic range stayed the same.

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