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What is a Complementary Metal Oxide Semiconductor?

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  • Written By: Siler
  • Edited By: C. Wilborn
  • Last Modified Date: 11 September 2016
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A complementary metal oxide semiconductor, or CMOS, is the basic logic controller that is used in an integrated circuit. Complementary metal oxide semiconductor design technology is traditionally found in microprocessors used in computers, computer memory, and mobile printed surface board technologies, such as mobile phones and handheld computing devices. The key selling point of a CMOS device is its very low rate of power consumption, as compared to the other logic technology available, the transistor-transistor logic (TTL).

The CMOS utilizes two different metal combinations to establish the logic gateway that enters into the complementary metal oxide semiconductor. As such, the resistance between these two metals is very high. Consequently, by following Ohm's law that voltage equals current times resistance, the higher the resistance, the less current that is required to maintain a given voltage.

Another important design feature of CMOS is its AND/OR logic controller. What this controller allows is for the unit only be operational during a dynamic phase. In real-world terms, this means that the logic controller is similar to a faucet that only allows water to flow when it is demanded by a user and doesn't always have to have water flowing in order to operate.

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The CMOS controller will consume half the power of a logic controller that requires power to operate both in the dynamic and static positions. This efficient use of power to conduct various logic functions makes this type of logic controller ideal for applications where power supply is very limited. One example is a cell phone that needs to be operational for several hours or even days at a time without being plugged back in to recharge the battery.

The first complementary metal oxide semiconductor was patented in 1967 by Frank Wanless, an engineer with Fairchild Semiconductor. The first successful commercial use of the CMOS was established by RCA company in 1968. Initially, the biggest drawback to using a CMOS logic unit was the speed at which the logic functions could be performed. The TTL controller, while similar, was able to perform functions in a faster rate of speed, even while consuming more power. With the inherent design feature of lower power consumption, engineers were soon able to increase the speed of the performance of the CMOS to a level that was much faster than traditional TTL controllers.

Complementary metal oxide semiconductors were originally constructed of aluminum. Improvements in the semiconductor industry introduced new metals, such as tantalum and polysilicon, however. These metals and other compounds generate much less heat and are much less prone to failure than traditional aluminum components. The less heat an element produces, the more efficiently it uses the power required for various function, using less battery power.

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