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26 Mar 2015

What are the Benefits of CMOS Sensors Compared with CCD Sensors?

CMOS sensors long ago caught up to the performance offered by CCD sensors and are playing to their specific strengths. Today's CMOS sensors are expected to offer extraordinarily high frame rates, strong image quality and very strong sensitivity.

CMOS technology also stands out for its performance at different light intensities, energy consumption, speed and price when compared with CCD technology . For your application, this means for example significantly higher throughput on inspected parts and rapid drops in camera and system costs, all without sacrificing on image quality.

CMOS vs. CCD - A Closer Look at the Technical Details

  • In the past, CMOS sensors were known for being significantly less efficient at converting the incoming light. This is no longer the case. Improvements such as on-board micro-lens arrays on chips ensure that today's CMOS sensors achieve the same or even better sensitivity than CCD sensors.
  • Thanks to their architecture, CMOS sensors allow for significantly higher frame rates. Combined with improved sensitivity and the latest global shutter technology from ams, Sony and ON Semiconductor, it's now possible to capture a very rapid sequence of images. This in turn increases performance in your applications - such as more parts inspected per second or clearer images of traffic violations. CMOS sensors often have a higher full well capacity (or saturation capacity). The full well capacity is the maximum number of electrons per pixel, whereby the ratio between the full well capacity and the sensitivity threshold defines the dynamic range that the sensor can cover. So while a CCD sensor offers a better sensitivity threshold, the CMOS sensor more than makes up for it in its dynamic performance through its superior saturation capacity. As such, CMOS and CCD sensors perform at almost equal dynamics levels. The Sony IMX174 sensor is a good example of a CMOS sensor that is superior in its dynamic range compared with all comparable CCD sensors.
  • While several years ago one might reasonably have said that CCD sensors were the better choice in low-light situations, while CMOS sensors were a nose ahead in brightly lit situations. The image quality for CMOS sensors has improved so drastically of late, however, that they are now well suited for low-light situations as well.
  • Their advantages in brightly lit situations are still there too. When a CCD pixel is overexposed, the extra electrons can "slosh" onto the neighboring pixels. This produces an effect known as "blooming," where very bright structures within the image sprawl into darker ones. When the charge on the CCD sensor is transported after exposure in very bright light situations, the CCD sensors sometimes produce bright strips on the image. These white areas are part of an effect known as "smearing," perhaps most easily identified when a car drives at night towards the camera with its headlights on. Neither effect occurs with CMOS sensors.
  • The latest cameras with CMOS sensors even come with global shutter functionality, such as our ace models with Sony's "Pregius" sensor line, the "PYTHON" from ON Semiconductor and the "CMV" from ams. This means no more of the artifacts that can occur with rolling shutter cameras.

Sony announced in March 2015 that it was discontinuing its entire line of CCD sensors. This puts the end in sight for further development of CCD-based technology. Future sensors will instead be based on CMOS. All in all, CMOS sensors match up to CCD technology in every way. They work at fast speeds, are high-resolution and demonstrate improved noise performance.

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