Overview of NMOS Transistor
Modern digital memories, processors, and logic devices all use the metal oxide semiconductor transistor, or MOS transistor, as a fundamental component. It is a majority-carrier device in which a voltage applied to the gate modulates the current flowing through a conducting channel between the source and the drain. This MOS transistor is essential to many analog and mixed-signal integrated circuits. This transistor can be used as an amplifier, a switch, or a resistor thanks to its versatility. PMOS and NMOS are the two types of MOS transistors.
NMOS Transistor Symbol
Overview of PMOS Transistor
The PMOS transistor, also known as a P-channel metal oxide semiconductor, is a form of transistor in which the channel or gate area uses p-type dopants. This transistor is the NMOS Transistor's exact opposite. These transistors contain three major terminals: the source, gate, and drain. The source terminal of the transistor is constructed from a p-type substrate, whereas the drain terminal is constructed from an n-type substrate. The current in this transistor is conducted by charge carriers, such as holes. The symbols for PMOS transistors are displayed below.
PMOS Transistor Symbol
The Function of an NMOS Transistor
The NMOS transistor functions as a closed circuit when it receives a non-zero voltage, which means that the connection between the source terminal and the drain functions as a wire. As a result, the source receives current flowing from the gate terminal. The connection between the source terminal and the drain will be destroyed when this transistor obtains a voltage of about 0V, forming an open circuit, which causes current to flow from the gate terminal to the drain.
The Function of the PMOS Transistor
The way a p-type transistor operates is very different from an n-type transistor. When this transistor receives non-zero voltage, it will create an open circuit, which prevents electricity from flowing from the gate (G) terminal to the source (S). Similar to that, when this transistor receives a voltage of about 0 volts, it forms a closed circuit, meaning current flows from the gate (G) terminal to the drain (D).
An inversion bubble is another name for this one. Therefore, the primary purpose of this circle is to invert the value of the input voltage. This inverter will convert a voltage of one at the gate terminal to zero and operate the circuit as necessary. Therefore, the PMOS and NMOS transistors serve quite different purposes. It will transform into a CMOS (complementary metal-oxide semiconductor) circuit if we combine them into a single MOS circuit.
PMOS Transistor Working
NMOS Transistor Cross Section
A typical NMOS transistor consists of a p-type body that is sandwiched between two neighboring n-type semiconductor areas known as the source and the drain. A regulating gate on this transistor regulates the flow of electrons between the source and drain terminals.
The PN junctions of the source and drain in this transistor are reverse-biased because the transistor's body is grounded. An electric field will begin to develop as the voltage at the gate terminal is raised, drawing free electrons to the Si-SiO2 interface's base.
Electrons eventually fill all the holes once the voltage is high enough, and a thin region below the gate known as the channel is inverted to function as an n-type semiconductor. The transistor will turn ON as a result of allowing current to flow through this, creating a conducting lane from the source terminal to the drain. If the gate terminal is grounded then no current flows in the reverse-biased junction so the transistor will be turned OFF.
NMOS Transistor Cross Section
PMOS Transistor Cross Section
Below is a cross-section of a PMOS transistor. A pMOS transistor is constructed with an n-type body and two neighboring p-type semiconductor regions. According to the diagram, this transistor contains a regulating gate that regulates the flow of electrons between its source and drain terminals. The body of the pMOS transistor is maintained at a positive voltage. The source and drain terminals are reverse-biased after the gate terminal is positive. Once this occurs, there will be no current flowing, turning the transistor OFF.
Positive charge carriers will be drawn to the bottom of the Si-SiO2 interface if the voltage supply at the gate terminal is reduced. When the voltage drops low enough, the channel inverts and allows current to flow from the source terminal to the drain, creating a conducting pathway. These transistors often only have two distinct values, such as 1 & 0, when dealing with digital logic (ON and OFF). The logic high (1) value in digital circuits is represented by the transistor's positive voltage, or VDD. In TTL logic, the VDD voltage levels were typically around 5V. Currently, transistors are unable to resist such high voltages because their operating range is usually between 1.5V and 3.3V. Frequently, the low voltage is referred to as GND or VSS. Therefore, VSS stands for logic "0," and it is often set to 0V.
Cross Section of PMOS Transistor
NMOS Transistor Circuit
Below is a diagram of a NOT gate made of NMOS and PMOS transistors. By connecting a pMOS transistor to the source and a nMOS transistor to the ground, we can combine pMOS and nMOS transistors to create a NOT gate. So, circuit will serve as our first example of a CMOS transistor. One kind of logic gate that produces an inverted input as an output is the NOT gate. An inverter is another name for this gate. The result will be "1" if the input is "0."
NMOS Transistor Circuit
The pMOS transistor at the top and the nMOS transistor at the bottom receive the input when it is zero. The input value "0" is converted into "1" once it reaches the pMOS transistor. Consequently, the source link is severed. Therefore, if the connection to the drain (GND) is also closed, this will produce a logic "1" value. We are aware that the nMOS transistor won't flip the input value; as a result, it accepts zero as is and creates an open circuit to the drain. As a result, the gate generates a logical value of 1.
The above circuit's two transistors receive the value "1" if the input value is also "1". The '1' value will become a 'o' after it is received by the pMOS transistor. Consequently, the pathway to the source is free. The nMOS transistor won't become inverted once it receives the value "1". The input value therefore stays at 1. The connection to the GND is closed once the nMOS transistor has received one value. As a result, it will produce an output of logic "0."
PMOS Transistor Circuit
The PMOS and NMOS transistor-based NAND gate architecture is depicted below. In digital electronics, a NAND gate is typically a logic gate, also known as a NOT-AND gate. This gate's output complements an AND gate and is low (0) only if both of its inputs are high (1). It produces high output values if either of the two inputs is LOW (zero). The A input of the pMOS will produce "1" and the A input of the nMOS will produce "0" in the logic circuit shown below if the inputs A and B are both zeros. So, this logic gate generates a logical ‘1’ because it is connected to the source by a closed circuit & detached from the GND through an open circuit.
PMOS Transistor Circuit
When A is "0" and B" is "1," A input of the pMOS will produce a "1," and A input of the NMOS will produce a "0." Due to its closed circuit connection to the source and open circuit separation from the GND, this gate will yield a logical one. When A is "1" and B is "0," the "B" input of pMOS will produce a high output (1) while the "B" input of NMOS will produce a low output (0). Due to its closed circuit connection to the source and open circuit separation from the GND, this logic gate will produce a logical 1.
When A and B are both 1, A input from a pMOS will result in a zero, whereas A input from a nMOS will result in a '1'. As a result, we also need to check the B input of pMOS and nMOS. The B input of a pMOS will produce a "0," while the B input of a nMOS will produce a "1." Because it is disconnected from the source by an open circuit and linked to the GND by a closed circuit, this logic gate will produce a logical "0."
Characteristics of the NMOS transistor
The NMOS transistor's I-V properties are displayed below. the voltage between the source and drain (VDS) as well as between the gate and source terminals (VGS). Therefore, the curves between IDS and VDS are obtained by simply grounding the source's terminal, setting an initial VGS value, and stepping the VGS value from "0" to "VDD" to set the VDS to the highest DC voltage value. As a result, the IDS are very small and will exhibit a linear trend for very low VGS. When the VGS value rises, IDS improves and develops the following dependencies on VGS & VDS.
Characteristics of the NMOS transistor
Characteristics of the PMOS Transistor
Below are the I-V characteristics of a PMOS transistor. In order to determine the relationship between the drain to source current (I DS) and its terminal voltages, such as linear & saturation regions, these properties are divided into two sections.
While the IDS is steady and independent of VDS in the saturation zone, it increases linearly when the VDS (drain to source voltage) is increased in a liner region. A method similar to that used for the NMOS transistor is used to derive the principal relationship between the ISD (source to drain current) and its terminal voltages. The sole difference in this scenario is that the charge carriers in the inversion layer are now just holes. When the holes move from source to drain then the flow of current is also the same.
Characteristics of the PMOS Transistor
PMOS vs NMOS Transistor
| PMOS Transistor |
NMOS Transistor |
| P-channel metal-oxide-semiconductor transistor is referred to as a PMOS transistor. |
N-channel metal-oxide-semiconductor transistor is referred to as an NMOS transistor. |
| Simple n-type semiconductors are used to provide the source and drain in PMOS transistors. |
P-type semiconductors are used to make the source and drain in NMOS transistors. |
| This transistor's substrate is comprised of an n-type semiconductor. |
This transistor's substrate is comprised of p-type semiconductor material. |
| In PMOS, holes make up the majority of the charge carriers. |
Electrons make up the majority of charge carriers in NMOS. |
| PMOS devices are not smaller than NMOS ones. |
NMOS devices are considerably more compact than PMOS devices. |
| Compared to NMOS devices, PMOS devices cannot be switched more quickly. |
NMOS devices can be switched faster than PMOS devices. |
| Once a low voltage is applied to the gate of a PMOS transistor, it will begin to conduct. |
Once a high voltage is applied to the gate, an NMOS transistor will begin to conduct. |
| These are more noise-resistant. |
These are not noise-proof in comparison to PMOS. |
| This transistor's threshold voltage (Vth) is a negative value. |
This transistor's threshold voltage (Vth) is a positive value. |
Conclusion of PMOS vs NMOS Transistor
The structural differences between PMOS and NMOS are the main difference between the two systems. A PMOS device uses P-type as the substrate and N-type doped semiconductors as the source and drain, in contrast to NMOS. An NMOS (negative-MOS) transistor forms a closed circuit when exposed to a non-zero voltage; it forms an open circuit when exposed to a voltage of roughly 0 volts. When a PMOS (positive-MOS) transistor receives a non-zero voltage, it produces an open circuit, and when it receives a voltage of roughly 0 volts, it makes a closed circuit. Because to its benefits, NMOS is used more commonly than PMOS, however due to its polarization properties, PMOS is still required in many applications.
Additionally, analog and digital microelectronics typically use both NMOS and PMOS. Particularly, both PMOS and NMOS are compatible with the CMOS (complementary MOS) structure, one of the most popular MOS structures. Even though PMOS is less noise-prone, the ON resistance of an NMOS is around half that of a PMOS. NMOS transistors offer a smaller footprint than PMOS transistors for the same output current, and NMOS is also faster than PMOS. In conclusion, it is recommended that NMOS and PMOS be designed to operate symmetrically.
PMOS vs NMOS FAQ
What distinguishes NMOS and PMOS transistors from one another?
The n-type transistor operates in the opposite manner to the p-type transistor. When the voltage is non-negligible, the nMOS will establish a closed circuit with the source, but the pMOS will make an open circuit with the source.
What benefits do PMOS have over NMOS?
Furthermore, PMOS will conduct and NMOS will not conduct when a low voltage is given to the gate. Since the carriers in NMOS, which are electrons, move twice as quickly as the carriers in PMOS, which are holes, NMOS is thought to be quicker than PMOS. However, PMOS devices are more noise-resistant than NMOS devices.
Why do we prefer NMOS over CMOS?
For the design of embedded systems, CMOS is preferred over NMOS. Because NMOS propagates only logic 1, or VDD, while CMOS propagates both logics o and 1. After going through one NMOS gate, the O/P would be VDD-Vt. CMOS technology is therefore recommended.
What are NMOS and PMOS, respectively?
A microelectronic circuit known as an N-channel metal-oxide semiconductor (NMOS) is utilized in the design of complementary metal-oxide semiconductor (CMOS) and logic and memory devices. More NMOS transistors can be fitted onto a single chip than their P-channel metal-oxide semiconductor (PMOS) sibling, and they are faster.
Why do we use PMOS?
Because of the higher on resistance caused by the decreased mobility and saturation velocity of the holes, PMOS transistors are connected in series. As a result, NAND gates are chosen over NOR gates. R1 Either the up network is pulling up on the output while using static CMOS logic.