Define CMOS inverter and its role in digital logic.
1 Answer
A CMOS (Complementary Metal-Oxide-Semiconductor) inverter is a fundamental building block of digital logic circuits. It serves as the basic unit for transforming binary signals (0s and 1s) between their complementary states. The CMOS inverter is constructed using both NMOS (N-type Metal-Oxide-Semiconductor) and PMOS (P-type Metal-Oxide-Semiconductor) transistors.
Here's how a CMOS inverter works:
NMOS Transistor: The NMOS transistor is a type of field-effect transistor (FET) where the current flow between the source and drain terminals is controlled by the voltage applied to the gate terminal. When a positive voltage (logic 1) is applied to the gate of the NMOS transistor, it becomes conductive, allowing current to flow between its source and drain terminals. This effectively connects the output node to the ground (0V) and pulls it down, resulting in a low output (logic 0).
PMOS Transistor: The PMOS transistor is also a type of FET, but its operation is opposite to that of NMOS. When a negative voltage (logic 0) is applied to the gate of the PMOS transistor, it becomes conductive, allowing current to flow between its source and drain terminals. This connects the output node to the supply voltage (VDD), which is typically a positive voltage. As a result, the output node is pulled up to VDD, creating a high output (logic 1).
By combining these two transistors in a complementary manner, the CMOS inverter functions as follows:
When the input is at logic 0 (ground), the NMOS transistor is on and provides a low-resistance path to ground, while the PMOS transistor is off. This pulls the output node to a low voltage, resulting in a logic 1 output.
When the input is at logic 1 (VDD), the NMOS transistor is off and the PMOS transistor is on, providing a low-resistance path to VDD. This raises the output node to a high voltage, resulting in a logic 0 output.
The primary role of the CMOS inverter in digital logic is to invert the input signal's logic state. It is a key component in various digital circuits, such as logic gates, flip-flops, multiplexers, and more complex circuits like processors and memory units. CMOS technology is popular due to its low power consumption, high noise margin, and compatibility with integrated circuit fabrication processes, making it widely used in modern digital electronic systems.
Here's how a CMOS inverter works:
NMOS Transistor: The NMOS transistor is a type of field-effect transistor (FET) where the current flow between the source and drain terminals is controlled by the voltage applied to the gate terminal. When a positive voltage (logic 1) is applied to the gate of the NMOS transistor, it becomes conductive, allowing current to flow between its source and drain terminals. This effectively connects the output node to the ground (0V) and pulls it down, resulting in a low output (logic 0).
PMOS Transistor: The PMOS transistor is also a type of FET, but its operation is opposite to that of NMOS. When a negative voltage (logic 0) is applied to the gate of the PMOS transistor, it becomes conductive, allowing current to flow between its source and drain terminals. This connects the output node to the supply voltage (VDD), which is typically a positive voltage. As a result, the output node is pulled up to VDD, creating a high output (logic 1).
By combining these two transistors in a complementary manner, the CMOS inverter functions as follows:
When the input is at logic 0 (ground), the NMOS transistor is on and provides a low-resistance path to ground, while the PMOS transistor is off. This pulls the output node to a low voltage, resulting in a logic 1 output.
When the input is at logic 1 (VDD), the NMOS transistor is off and the PMOS transistor is on, providing a low-resistance path to VDD. This raises the output node to a high voltage, resulting in a logic 0 output.
The primary role of the CMOS inverter in digital logic is to invert the input signal's logic state. It is a key component in various digital circuits, such as logic gates, flip-flops, multiplexers, and more complex circuits like processors and memory units. CMOS technology is popular due to its low power consumption, high noise margin, and compatibility with integrated circuit fabrication processes, making it widely used in modern digital electronic systems.