What is CMOS Technology?

CMOS technology is widely used in the fabrication of integrated circuits. CMOS is an abbreviation for "Complementary Metal Oxide Semiconductor." This technique is used in microprocessors, batteries, and digital sensors, among other electronic components, due to numerous important advantages. To accomplish diverse logic functions, this technology employs both NMOS and PMOS. Matching features are incorporated into both the N and P MOSFET channels. 
Prior to CMOS logic, PMOS and NMOS logic were frequently utilized to create logic gates. PMOS was eventually superseded by NMOS Technology, which was previously the standard IC fabrication technology. CMOS was initially slower and more expensive than NMOS. NMOS technology's key advantages are its simple physical method, functional density, processing speed, and manufacturing efficiency. Electrical asymmetry and static power dissipation are the major drawbacks of NMOS technology. These disadvantages are mitigated by the use of CMOS technology. The main advantage of CMOS is the low power dissipation, which occurs mainly during circuit switching. This leads in significantly improved performance since it enables for the integration of additional CMOS gates on one IC.


N-channel MOSFETs are made up of an N-type source and drain that are diffused on a P-type substrate. Electrons make up the vast majority of carriers. The NMOS will conduct when the gate voltage is sufficiently high; otherwise, it will not. NMOS is considered to be faster than PMOS since the majority of carriers (electrons) travel faster than holes.

NMOS Transistor 


A Source and Drain are also diffused on a substrate in P-channel MOSFETs. The source is of the P type, while the substrate is of the N type. The vast majority of carriers are voids. When a low voltage is provided, PMOS will conduct. The PMOS will not conduct if a high voltage is applied to the gate.

PMOS Transistor 


As CMOS technology employs both N-type and P-type transistors in the creation of logic functions, a signal that turns on one transistor type is utilized to turn off the other. This replaces the need for pull-up resistors with simple switches. N-type MOSFETs are organized in a pull-down network between the output and the low voltage supply rail (VSS or ground) in CMOS logic gates, whereas P-type MOSFETs are positioned in a pull-up network between the output and the higher-voltage rail (typically VDD). As a result, when the P-type MOSFET is turned off, the N-type MOSFET is turned on, and vice versa. For any given input pattern, one of the networks is turned on and the other is turned off. High speed, low power dissipation, high noise margins in both states, and a wide range of source and input voltages (fixed source voltage) are all advantages of CMOS.

CMOS Logic Gate

CMOS (CMOS Logic Gates)

1) Inverter CMOS

The most basic CMOS logic gate is the inverter. The circuit is made up of PMOS and NMOS FETs. The gate voltage for both transistors is provided by input A, while the output is provided by Y.

CMOS Inverter

The NMOS transistor is powered by VSS or ground, while the PMOS transistor is powered by VDD. When the input (A) is low (VDD, 0 V, Logic 0), the NMOS is turned off and the PMOS is turned on. VDD will be seen at the output via the P-channel MOSFET circuit. As a result, with the circuit pushed up to VDD, there is output (Logic 1). When the input is high (VDD, Logic 1), the PMOS is turned off and the NMOS is turned on. The output has been brought down and is hence low (Logic 0).

what is CMOS 


Two N-channel MOSFETs are connected in series between Y (output) and GND in a 2-input NAND gate, and two P-channel MOSFETs are connected in parallel between VDD and Y


At least one of the NMOS transistors will be turned off if either A or B is low (Logic 0). Because the NMOS transistors are coupled in series, this interrupts the flow from Y to GND. In this situation, however, at least one of the PMOS transistors is turned on, completing the circuit from Y to VDD. This raises the output Y (Logic 1). For Y to be low, both A and B must be high in order for both NMOS transistors to be ON and the path from Y to GND to be complete. Y will be positive for all other input combinations. The NAND logic gate truth table is shown below.

CMOS NAND Gate Truth Table 

3) CMOS NOR Gate

The NMOS transistors of a 2-input NOR gate are connected in parallel, whereas the PMOS transistors are connected in series. At least one NMOS transistor pulls the output low when at least one of the inputs is high. Only when both inputs are low is the output high.

Complementary MOS NOR Gate 

The NOR logic gate truth table is shown below.


Because of its efficiency in using electric power and adaptability, CMOS is the dominating technique for IC production. The low-power design produces less heat and is the most dependable of the present technologies. Depending on the circuit design, P-type and N-type transistors can be arranged to produce logic gates.

Prasun Barua

Prasun Barua is an Engineer (Electrical & Electronic) and Member of the European Energy Centre (EEC). His first published book Green Planet is all about green technologies and science. His other published books are Solar PV System Design and Technology, Electricity from Renewable Energy, Tech Know Solar PV System, C Coding Practice, AI and Robotics Overview, Robotics and Artificial Intelligence, Know How Solar PV System, Know The Product, Solar PV Technology Overview, Home Appliances Overview, Tech Know Solar PV System, C Programming Practice, etc. These books are available at Google Books, Google Play, Amazon and other platforms.


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