FTII People

Bakul asked me last night the difference between a CCD and a CMOS.

thats a difficult one, since these are two different technologies and each has its own strengths and weaknesses, and neither can be said to be better or worse than the other. Nikon uses CCDs for most of its cameras and Canon uses CMOS sensors. Both camera systems are used by top professionals worldwide.

heres some stuff I found online, from howstuffworks.com:

Both CCD (charge-coupled device) and CMOS (complimentary metal-oxide semiconductor) image sensors start at the same point -- they have to convert light into electrons. If you have read the article How Solar Cells Work, you understand one technology that is used to perform the conversion. One simplified way to think about the sensor used in a digital camera (or camcorder) is to think of it as having a 2-D array of thousands or millions of tiny solar cells, each of which transforms the light from one small portion of the image into electrons. Both CCD and CMOS devices perform this task using a variety of technologies.

The next step is to read the value (accumulated charge) of each cell in the image. In a CCD device, the charge is actually transported across the chip and read at one corner of the array. An analog-to-digital converter turns each pixel's value into a digital value. In most CMOS devices, there are several transistors at each pixel that amplify and move the charge using more traditional wires. The CMOS approach is more flexible because each pixel can be read individually.

CCDs use a special manufacturing process to create the ability to transport charge across the chip without distortion. This process leads to very high-quality sensors in terms of fidelity and light sensitivity. CMOS chips, on the other hand, use traditional manufacturing processes to create the chip -- the same processes used to make most microprocessors. Because of the manufacturing differences, there have been some noticeable differences between CCD and CMOS sensors.

• CCD sensors, as mentioned above, create high-quality, low-noise images. CMOS sensors, traditionally, are more susceptible to noise.
  Because each pixel on a CMOS sensor has several transistors located next to it, the light sensitivity of a CMOS chip tends to be lower. Many of the photons hitting the chip hit the transistors instead of the photodiode.
  CMOS traditionally consumes little power. Implementing a sensor in CMOS yields a low-power sensor.
  CCDs use a process that consumes lots of power. CCDs consume as much as 100 times more power than an equivalent CMOS sensor.
  CMOS chips can be fabricated on just about any standard silicon production line, so they tend to be extremely inexpensive compared to CCD sensors.
  CCD sensors have been mass produced for a longer period of time, so they are more mature. They tend to have higher quality and more pixels.

Based on these differences, you can see that CCDs tend to be used in cameras that focus on high-quality images with lots of pixels and excellent light sensitivity. CMOS sensors traditionally have lower quality, lower resolution and lower sensitivity. CMOS sensors are just now improving to the point where they reach near parity with CCD devices in some applications. CMOS cameras are usually less expensive and have great battery life.

heres an interesting comparison from DALSA the company that makes image sensors:

Kodak on CCD vs CMOS

At a high level, image sensors can be grouped into two general camps - charge coupled device (CCD) sensors and sensors that use complimentary metal oxide semiconductor (CMOS) technology. Up until now, almost all consumer digital cameras have used CCD sensors. But recently, Kodak announced the EASYSHARE C513 Camera - the first EASYSHARE camera to use a CMOS image sensor (the KODAK KAC-05011, to be precise). So we thought it might be interesting to give the lowdown on this change and the current state of CCD and CMOS technologies by posing a few questions.

What's the major difference between CCD and CMOS sensor technologies - are they really that different from each other?
CCD technology was developed specifically for imaging - converting light into electrons - so in general it provides very high image quality. However, while CCD sensors excel in this area, that's all they can do - they need additional support chips to convert that charge into a digital signal, provide the proper pulse sequences to clock out information from pixels in the sensor array, etc.
CMOS image sensors, on the other hand, share the same base technology that is used for general electronic components, like computer processors or memory chips. That means that a single CMOS image sensor can not only convert light into electrons, but also handle some of these other support functions all on a single piece of silicon. Because a CMOS sensor can be "smarter" than a CCD sensor, the use of CMOS image sensors can result in a simpler camera design (because fewer parts are required). CMOS designs also tend to run at lower voltages, which helps to reduce power consumption (leading to longer battery life).
The problem, of course, is that the image quality available from CMOS image sensors historically has not been as good as what you can get from CCDs. So you needed to trade off these two points - image quality vs. integration and power. That's why you've tended to see CMOS used in applications like camera phones (where small size and battery life are key) and CCD for other consumer and professional cameras (where image quality is still paramount).


red the entire interview here