Question

CMOS technology is preferred for

• A. Oscillators
• B. Resistors
• C. High power circuits
• D. Low power circuits

Hint:

CMOS circuits draw virtually zero static power when resting in a steady state. Current flows almost exclusively during logic level transitions, making it the choice for battery-powered and highly integrated systems.

Answer 1

The Correct Option is D

Concept: The acronym CMOS stands for Complementary Metal-Oxide-Semiconductor. This microelectronic design approach uses matched pairs of complementary \(n\)-type (NMOS) and \(p\)-type (PMOS) field-effect transistors to implement logic gates and integrated networks. The primary reason CMOS technology is widely preferred in modern integrated circuit manufacturing (such as microprocessors, microcontrollers, and static memory arrays) is its extremely low power consumption. Let's examine how a basic CMOS inverter operates to see why this is true:
• A CMOS inverter is built with a PMOS pull-up transistor connected to the positive supply voltage (\(V_{DD}\)) and an NMOS pull-down transistor connected to ground (\(V_{SS}\)), with their gates tied together at the input terminal.
• Static State (Input = Logic 0): The NMOS transistor turns completely off, and the PMOS transistor turns fully on. This pulls the output up to \(V_{DD}\). Since the NMOS device acts as an open circuit, no continuous current path exists from \(V_{DD}\) to ground.
• Static State (Input = Logic 1): The PMOS transistor turns completely off, and the NMOS transistor turns fully on. This pulls the output down to ground. Since the PMOS device acts as an open circuit, the current path from \(V_{DD}\) to ground remains blocked. Because one of the two transistors is always turned off in either stable logic state, the static leakage current is nearly zero. Significant power consumption occurs only during brief switching transitions (dynamic power consumption), which is required to charge and discharge parasitic capacitances: \[ P_{\text{dynamic}} = C_L \cdot V_{DD}^2 \cdot f \] where \(C_L\) represents the capacitive load and \(f\) represents the operating switching frequency. Because its static power dissipation is practically negligible, CMOS technology is highly preferred for designing low power circuits.