Difference between CMOS and NMOS Technology

The most popular MOSFET technology (semiconductor technology) available today is the CMOS technology or complementary MOS technology. CMOS technology is the leading semiconductor technology for ASICs, memories, microprocessors. The main advantage of CMOS technology over BIPOLAR and NMOS technology is the power dissipation – when the circuit is switched then only the power dissipates. This allows fitting many CMOS gates on an integrated circuit than in Bipolar and NMOS technology. This article discusses the difference between CMOS and NMOS technology.

Introduction to IC Technology

Silicon IC technology can be classified into types: Bipolar, a Metal oxide semiconductor, and BiCMOS.


IC Technology
IC Technology

The structure of the bipolar transistors has PNP or NPN. In these types of transistors, the small amount of current in the thicker base layer controls large currents between the emitter and collector. Base currents limit the integration density of the bipolar devices.

A metal-oxide-semiconductor is further classified into different technologies under PMOS, NMOS, and CMOS. These devices include a semiconductor, oxide, and a metal gate. Currently, Polysilicon is more commonly used as a gate. When the voltage is applied to the gate, then it controls the current between the source & drain. Since they consume less power and MOS allows higher integration.

BiCMOS Technology employs both CMOS and Bipolar transistors; these are integrated on the same semiconductor chip. CMOS technology offers high I/P and low O/P impedance, high packing density, symmetrical noise margins, and low power dissipation. BiCMOS technology has made it possible to combine bipolar devices and CMOS transistors in a single process at a reasonable cost to attain the high-density integration of MOS logic

The Difference Between CMOS and NMOS technology

The difference between CMOS technology and NMOS technology can be easily differentiated with their working principles, advantages, and disadvantages as discussed.


CMOS Technology

Complementary metal-oxide-semiconductor (CMOS technology) is used to construct ICs and this technology is used in digital logic circuits, microprocessors, microcontrollers, and static RAM. CMOS technology is also used in several analog circuits like data converters, image sensors, and in highly integrated transceivers. The main features of CMOS technology are low static power consumption and high noise immunity.

Complementary Metal Oxide Semiconductor
Complementary Metal Oxide Semiconductor

CMOS (complementary metal-oxide-semiconductor) is a battery-powered onboard semiconductor chip used to store the data within computers. This data ranges from the time of system time & date to hardware settings of a system for your computer. The best example of this CMOS is a coin cell battery used to power the memory of CMOS.

When a couple of transistors are in OFF condition, the combination of series draws significant power only during switching between ON & OFF states. So, MOS devices do not generate as much waste heat as other forms of logic. For example, TTL (Transistor-Transistor Logic) or MOS logic, which normally have some standing current even when not changing state. This allows a high density of logic functions on a chip. Due to this reason, this technology most widely used and is implemented in VLSI chips.

The Lifetime of CMOS Battery

The typical life span of a CMOS battery is approximately 10 years. But, this can change based on the utilization as well as environment wherever the computer exists in. If the CMOS battery damages, then the computer cannot maintain the exact time otherwise date once the computer is turned off. For instance, once the computer is turned ON, the date and time can be noticed like set to 12:00 P.M & January 1, 1990. So, this error mainly specifies that the battery of CMOS was failed.

CMOS Inverter

For any IC technology in the designing of digital circuits, the basic element is the logic inverter. Once the operation of an inverter circuit is carefully understood, the results can be extended to the design of the logic gates and complex circuits.

CMOS inverters are the most widely used MOSFET inverters, which are used in chip design. These inverters can operate at high speed and with less power loss. Also, the CMOS inverter has good logic buffer characteristics. The short description of the inverters gives a basic understanding of the working of the inverter. MOSFET states at different i/p voltages, and power losses due to electrical current.

CMOS Inverter
CMOS Inverter

A CMOS inverter has a PMOS and an NMOS transistor that is connected at the gate and drain terminals, a voltage supply VDD at the PMOS source terminal, and a GND connected at the NMOS source terminal, where Vin is connected to the gate terminals and Vout is connected to the drain terminals.

It is important to notice that the CMOS does not have any resistors, which makes it more power-efficient than a regular resistor-MOSFET inverter. As the voltage at the input of the CMOS device varies between 0 and 5 volts, the state of the NMOS and PMOS varies accordingly. If we model each transistor as a simple switch activated by Vin, the inverter’s operations can be seen very easily.

CMOS Advantages

CMOS transistors use electrical power efficiently.

  • These devices are used in a range of applications with analog circuits like image sensors, data converters, etc. The advantages of CMOS technology over NMOS are as follows.
  • Very low static power consumption
  • Reduce the complexity of the circuit
  • The high density of logic functions on a chip
  • Low static power consumption
  • High noise immunity
  • When CMOS transistors change from one condition to another, then they use electrical current.
  • In addition, the complimentary semiconductors limit the o/p voltage by working mutually. The outcome is a low-power design that provides less heat.
  • Because of this reason, these transistors have changed other earlier designs like CCDs in camera sensors as well as used in most current processors.

CMOS Applications

The CMOS  is one kind of chip, powered through a battery used to store the configuration of a hard drive as well as other data.

Usually, CMOS chips provide RTC (real-time clock) as well as CMOS memory within a microcontroller as well as a microprocessor.

NMOS Technology

NMOS logic utilizes n-type MOSFETs to operate through making an inversion layer within a p-type transistor. This layer is known as the n-channel layer which conducts electrons among n-type like source & drain terminals. This channel can be created by applying voltage toward the 3rd terminal namely the gate terminal. Similar to other metal oxide semiconductor field-effect transistors, nMOS transistors include different operation modes like a cut-off, triode, saturation & velocity saturation.

The logic family of NMOS utilizes N-channel MOSFETS. NMOS devices (N-channel MOS) need a smaller chip region for each transistor as compared through P-channel devices, where NMOS gives a higher density. The NMOS logic family gives high speed too because of the high mobility of the charge carriers within N-channel devices.

So, most of the microprocessors & MOS devices use NMOS logic otherwise some structural variations like DMOS, HMOS, VMOS & DMOS to reduce the propagation delay.

NMOS is nothing but a negative channel metal oxide semiconductor; it is pronounced as en-moss. It is a type of semiconductor that charges negatively. So that transistors are turned ON/OFF by the movement of electrons. In contrast, Positive channel MOS -PMOS  works by moving electron vacancies. NMOS is faster than PMOS.

Negative Channel Metal Oxide Semiconductor
Negative Channel Metal Oxide Semiconductor

The designing of NMOS can be done through two substrates like n-type as well as p-type. In this transistor, the majority of charge carriers are electrons. We know that the combination of PMPS and NMOS is called CMOS technology. This technology mainly utilizes less energy for operating at a similar output & generates low noise throughout its operation.

Once a voltage is given to the gate terminal, then the charge carriers like holes within the body are motivated away from the gate terminal. This permits the configuration of an n-type channel among the two terminals like source & the drain & the flow of current can be conducted using electrons from the two terminals from source to the drain using an induced n-type channel.

NMOS transistor is very easy to design as well as manufacture. The circuits using NMOS logic gates consume static power once the circuit is inactive. As DC current supplies throughout the logic gate once the output is low.

NMOS Inverter

An inverter circuit o/ps a voltage representing the opposite logic-level to its i/p. The NMOS inverter diagram is shown below which is constructed using a single NMOS transistor coupled with a transistor.

NMOS Inverter
NMOS Inverter

Difference between NMOS and CMOS

The difference between NMOS and CMOS is discussed in the tabular form.

CMOS

NMOS

CMOS stands for Complementary metal-oxide-semiconductorNMOS stands for N-type metal oxide semiconductor
This technology is used to make ICs which are used in different applications like batteries, electronic components, image sensors, digital cameras.NMOS technology is used to make logic gates as well as digital circuits
CMOS employs symmetrical as well as complementary pairs of MOSFETs like p-type & n-type MOSFETs for the operation of logic functionsThe operating of NMOS transistor can be done by making an inversion layer within a p-type transistor body
The modes of operation of CMOS are accumulation like depletion and inversionNMOS has four modes of operations that simulate other types of MOSFETs like a cut-off, triode, saturation & velocity saturation.
The CMOS characteristics are low static power consumption as well as high noise immunity and.The NMOS transistor characteristics are, when the voltage increases on the top electrode, then electrons attraction will be there toward the surface. At a specific voltage range, which we will shortly describe like the threshold voltage, where the density of electron at the outside will exceed the density of holes.
CMOS is used in Digital logic circuits, Microprocessors, SRAM (Static RAM) & MicrocontrollersNMOS is used to implement digital circuits as well as logic gates.
The CMOS logic level is 0/5VThe NMOS logic level mainly depends on beta ratio as well as poor noise margins
The transmission time of CMOS is tI=tfThe transmission time of CMOS is tI>tf
Layout of CMOS is more regularThe layout of NMOS is irregular
Load or drive ratio of CMOS is 1:1/2:1Load or drive ratio of NMOS is 4:1
Packing density is less, 2N device for N-inputsPacking density is denser, N+1 device for N-inputs
The power supply may change from 1.5 to 15V VIH/VIL, a fixed fraction of VDDThe power supply is fixed based on VDD
Transmission gate of CMOS will pass both logic wellOnly pass ‘0’, well pass ‘1’ will have VT drop
Pre-charging scheme of CMOS is, for both n & p are  accessible for the pre-charging bus to VDD/VSSSimply charges from VDD to VT except utilize bootstrapping
Power dissipation is zero in standbyIn NMOS, when output is ‘0’ then power dissipates

Why CMOS Technology is Preferred Over NMOS Technology

CMOS stands for Complementary Metal-Oxide-Semiconductor. On the other hand, NMOS is a metal oxide semiconductor MOS or MOSFET(metal-oxide-semiconductor field-effect transistor). These are two logic families, where CMOS uses both PMOS and MOS transistors for design and NMOS uses only FETs for design. CMOS is chosen over NMOS for embedded system design. Because, CMOS propagates both logic o and 1, whereas NMOS propagates only logic 1 that is VDD. The O/P after passing through one, the NMOS gate would be VDD-Vt. Therefore, CMOS technology is preferred.

 In CMOS logic gates, a set of n-type MOSFETs is positioned in a pull-down network between the low-voltage power supply rail and the output. Instead of the load resistor of NMOS logic gates, CMOS logic gates have a collection of P-type MOSFETs in a pull-up network between the high-voltage rail and the output. Therefore, if both transistors have their gates connected to the same input, the p-type MOSFET will be on when the n-type MOSFET is off, and vice-versa.

CMOS and NMOS both inspired by the growth in digital technologies, that are used to construct the integrated circuits. Both CMOS and NMOS are used in many digital logic circuits and functions, static RAM, and microprocessors. These are used as data converters and image sensors for analog circuits and also used in Trans-receptors for many modes of telephone communication. While both CMOS and NMOS have the same function as transistors for both analog and digital circuits, but many people still choose the CMOS technology over the latter for its many advantages.

 As compared to the NMOS, the CMOS technology is top in quality. Especially, when it comes to its features like low-static power utilization and noise resistance, CMOS technology conserves energy and it does not produce heat. Though costly, a lot of people prefer CMOS technology due to its complex composition, which makes it hard for the black market to fabricate the technology used by the CMOS.

The CMOS technology and NMOS technology along with its inverters, differences are discussed in brief in this article. Therefore, CMOS technology is best for embedded system design. For a better understanding of this technology, please post your queries as your comments below.