CMOS (Complementary Metal-Oxide Semiconductor) is a type of technology that is used to construct integrated circuits. These semiconductors use both positive polarity (PMOS) and negative polarity (NMOS) circuits. This is beneficial because only one of the circuit types is on at any given time. This results in less power being needed in comparison to chips that have only one type of transistor. Since they rely on less power, CMOS chips have become incredibly attractive when building portable computers or other devices that require longer battery life. However, even personal computers contain a battery powered CMOS memory to keep the data, time, and system setup specifications kept in case the computer is unplugged or loses electricity.

Uses for CMOS

Since Frank Wanlass patented it in 1967, CMOS has seen a great many implementations throughout the technology world. Some of those implementations are:

  • Microprocessors
  • Microcontrollers
  • Static RAM
  • Image sensors
  • Data converters
  • Certain transceivers

Composition

The output of a CMOS is the inversion of its input. What that means is that the output of both the PMOS and the NMOS are complementary to each other. They rely on each other to function properly. When the input is low from a source, the output is high. On the flip side, when the input is high, the output is low.

When a low voltage is applied to a PMOS transistor, there is low resistance between the source and the drain contacts. However, there is high resistance when a high voltage is applied. The exact opposite occurs for NMOS. When there is a low voltage, there is high resistance between the source and the drain. When there is a high voltage, there is a low resistance. What this allows is for both the PMOS and the NMOS to function simultaneously, thus cutting the amount of energy required. Therefore, it is clear that these two – PMOS and NMOS are complementary to each other.

A CMOS circuit is created in such a way to guarantee that there is always a path between the output to the power’s source or the ground. In other words, all paths to the ground must have a complement set of paths to the power source. This is accomplished by having NMOS transistors in parallel and PMOS transistors in series. At the same time, there are PMOS transistors in parallel with NMOS transistors in series. This guarantees that there is duality between the PMOS and NMOS transistors, which is important for keeping the pathways open between the output and the power source.