{"id":7606,"date":"2011-07-07T09:42:56","date_gmt":"2011-07-07T07:42:56","guid":{"rendered":"https:\/\/www.adimec.com\/?p=7606"},"modified":"2018-07-27T17:14:03","modified_gmt":"2018-07-27T15:14:03","slug":"ccd-vs-cmos-image-sensors-in-defense-cameras","status":"publish","type":"post","link":"https:\/\/www.adimec.com\/ja\/ccd-vs-cmos-image-sensors-in-defense-cameras\/","title":{"rendered":"CCD vs. CMOS Image Sensors in Defense Cameras"},"content":{"rendered":"
CMOS sensor based defense cameras are gaining ground, but for long-term, reliable, high image quality applications, CCDs will continue to be the preferred option for a while.<\/strong><\/p>\n On February 8th<\/sup>, we discussed the\u00a0CCD vs. CMOS sensors in machine vision cameras<\/a>.\u00a0 We discussed that\u00a0CMOS image sensors<\/a>\u00a0have shown significant improvements in quality and are quickly approaching that of\u00a0CCD sensors<\/a>, especially when sophisticated camera technology is used to optimize image uniformity. Our conclusion was that more and more, CMOS-sensor based cameras are a good option for many machine vision applications now and this trend will continue.[1]<\/p>\n As\u00a0Adimec<\/a> also serves the\u00a0defense market<\/a>, this has us considering whether CMOS sensors are also gaining the advantage there.\u00a0 As with most things in technology, it is not a simple yes or no answer and depends on the specific needs of the application.<\/p>\n Depending which of the special requirements in the defense industry is most important, can help determine which technology is the best fit, such as<\/p>\n NIR Sensitivity<\/strong><\/p>\n Typically the sensitivity of the sensor is evaluated based on the quantum efficiency, QE, or the chance that one photon generates one electron in the sensor at a given wavelength.\u00a0 While this is a good indicator, it is also important to consider the read noise of the sensor.\u00a0 These two combined give the overall sensitivity of the sensor, or the minimum amount of light you can see.\u00a0 In general, CMOS sensors have a higher QE in the NIR due to their design structure, and this can be further optimized by producing the sensor using a thicker epitaxial layer (shown as CMOS 1-b in Figure 1 below).\u00a0 So for instance, at 800nm, the CMOS sensor with the thicker epitaxial layer has the best QE.<\/p>\n Figure 1.\u00a0 QE versus wavelength for various sensors<\/strong><\/p>\n CCD 1 and CCD 2 are Interline Transfer CCDs; CMOS 1 and CMOS 1-b are CMOS sensors with a Global Shutter.<\/p>\n But, when read noise is also considered as shown in Figure 2, there are CCD sensors, such as CCD sensor number 1 in Figure 2, that actually have the better sensitivity at 800 nm.<\/p>\n Figure 2. QE\/Read Noise (Sensitivity) vs. Wavelength<\/strong><\/p>\n Performance in Harsh Outdoor Conditions<\/strong><\/p>\n Cameras with either type of sensor can be ruggedized to perform in high shock and vibration environments.\u00a0 The effects from high temperatures are different, though.\u00a0 The numbers shown in the above figures 1 and 2 are for 25\u00b0C and read noise rises with the sensor temperature. The sensitivity advantage of CCD becomes even more pronounced as CCDs have lower noise at higher temperatures.\u00a0 Because of optimized processes and structures, CCDs also perform much better in terms of image uniformity at higher temperatures.<\/p>\n CMOS sensors can still perform well, but may require additional camera functionality or even cooling to achieve the same noise performance and image uniformity at higher ambient temperatures.<\/p>\n\n
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