By: Arthur Cooper
Submitted: 2011-03-02 06:07:39 | Word Count: 664
What’s the difference, CMOS vs CCD? In the digital video security camera industry there are two types of sensors used to convert light images into (ultimately) electronic images. Those two sensors are the Complementary Metal Oxide Semiconductor or CMOS and the Charged Coupled Device or CCD. In the following article, we’ll take a closer look at each and see how they are both similar and different.
Though they are entirely different, both electronic sensors yield the same end result a digital photograph or digital video. So as often is the case when comparing the CMOS vs CCD, the first question asked is “Which is superior?” The answer to this is neither and both. Read on to find out why.
[ advertisement ]
First the CMOS and CCD sensors were both invented in the 1960-1970′s. Although we think of them today as sensors, both are actually different types of technologies used in creating Integrated Circuits (ICs). For example, CMOS technology is not only used for creating image sensors, but is also used to create microprocessors and Random Access Memory (RAM).
When comparing how they function, the CMOS vs CCD can both convert light into measurable electric charges that are further processed into electronic signals that are used to create digital video images. (Digital video images are basically a series of digital video photographs taken very rapidly, such as 30 per second. So when we mention these sensors and production of digital video, we are implying digital photographs as well.)
To get really technical, the CCD has a series of pixels that when struck by light create a charge that is transferred through a very low number of output nodes (most often only one). The charge is converted to a voltage that is buffered and relayed out of the IC as an analog signal. The analog signal is converted to a digital signal using an analog-to-digital converter (another IC). One key point in a CCD is that the entire pixel has the potential for light capture and therefore the output of the pixel’s uniformity is high; in other words, the image quality can be very high.
In contrast each of the CMOS’s pixels has their own charge conversion to voltage transfer. The CMOS often uses noise-correction, amplifiers, and digitizing circuits to ensure the output is digital. These extra electronic steps make the design of the CMOS more complex, reducing the area available for light capture for the pixels. In addition, since each individual pixel is doing its own processing work, the uniformity of the signal is not as high as that of the CCD.
Initially, one may score a point here in the CMOS vs CCD match for the CCD for higher quality. However, there are trade offs that exists with the CMOS and that is drastically lower static power consumption and to a certain extent, lower cost of the sensor itself. So, score a point for the CMOS as well.
Yet the cost issue is rather insignificant when comparing the same quality CMOS vs CCD sensor. These differences exist because of manufacturing process differences, but they are beyond the extent of our discussion for digital video security cameras. The truth is that as technology continues to increase, CCDs are being created that use less power consumption and CMOSs are being created that create a higher uniformity signal (or higher quality video image).
Here is a short summary our comparison of the CMOS vs CCD:
* The CCD chip produces an analog voltage. The CMOS chip produces a digital voltage (bits). Cameras using either sensor produce the same signal out of the camera, digital bits.
* The CMOS has a slightly better responsiveness than the CCD, but it has a lower uniformity or quality.
* The CMOS demands a very low-voltage low power consumption while the CCD requires a higher voltage constant higher power consumption.
See why we said earlier that when comparing the CMOS vs CCD neither and both were superior?
There is a tendency in the security camera industry to use a CMOS vs CCD for certain applications. Namely, cameras that use a portable expendable power supply, such as a one-time-use or rechargeable battery packs are more apt to use CMOS sensors because of their low static power requirements. Likewise, cameras that feature high quality, high resolution outputs have a tendency toward CCD sensors instead of CMOS sensors.
Therefore, in the CMOS vs CCD debate for digital video security cameras, it’s really a matter of manufacturers’ choice as to what is used.
