Describe the operation of a basic CMOS (Complementary Metal-Oxide-Semiconductor) inverter.
1 Answer
A CMOS inverter is a fundamental building block in digital integrated circuits and is widely used in digital logic design. It consists of complementary MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) pairs, one p-type (PMOS) and one n-type (NMOS), connected in series between the power supply and ground. The inverter's primary function is to convert an input signal from one logic level (high or low) to its complementary logic level.
Here's how a basic CMOS inverter operates:
Transistor Behavior:
PMOS (p-type MOSFET): When a positive voltage (logic low) is applied to its gate relative to its source (connected to the power supply VDD), it creates a conducting channel between its drain and source, allowing current to flow between VDD and the output node.
NMOS (n-type MOSFET): When a positive voltage (logic high) is applied to its gate relative to its source (connected to ground), it creates a conducting channel between its drain and source, allowing current to flow from the output node to ground.
Input Stage:
When the input signal is low (logic 0), the NMOS is turned off because its gate-source voltage is zero. At the same time, the PMOS is turned on because its gate-source voltage is positive. This creates a path from VDD to the output node, causing the output to be high (logic 1).
Output Stage:
The high output (logic 1) from the previous stage creates a positive voltage at the NMOS gate relative to its source, turning it on. Simultaneously, the low output (logic 0) from the previous stage creates a positive voltage at the PMOS gate relative to its source, turning it off.
Signal Inversion:
As a result of the input and output stages, the CMOS inverter effectively inverts the input signal. When the input is low, the output is high, and when the input is high, the output is low. This property is the basis for its use in digital logic circuits.
It's important to note that CMOS technology provides low power consumption and excellent noise immunity, making it a fundamental component in modern digital circuits. Additionally, CMOS logic gates can be easily scaled down in size, allowing for higher levels of integration on a chip.
Here's how a basic CMOS inverter operates:
Transistor Behavior:
PMOS (p-type MOSFET): When a positive voltage (logic low) is applied to its gate relative to its source (connected to the power supply VDD), it creates a conducting channel between its drain and source, allowing current to flow between VDD and the output node.
NMOS (n-type MOSFET): When a positive voltage (logic high) is applied to its gate relative to its source (connected to ground), it creates a conducting channel between its drain and source, allowing current to flow from the output node to ground.
Input Stage:
When the input signal is low (logic 0), the NMOS is turned off because its gate-source voltage is zero. At the same time, the PMOS is turned on because its gate-source voltage is positive. This creates a path from VDD to the output node, causing the output to be high (logic 1).
Output Stage:
The high output (logic 1) from the previous stage creates a positive voltage at the NMOS gate relative to its source, turning it on. Simultaneously, the low output (logic 0) from the previous stage creates a positive voltage at the PMOS gate relative to its source, turning it off.
Signal Inversion:
As a result of the input and output stages, the CMOS inverter effectively inverts the input signal. When the input is low, the output is high, and when the input is high, the output is low. This property is the basis for its use in digital logic circuits.
It's important to note that CMOS technology provides low power consumption and excellent noise immunity, making it a fundamental component in modern digital circuits. Additionally, CMOS logic gates can be easily scaled down in size, allowing for higher levels of integration on a chip.