Question

Which logic family has lowest power dissipation?

• A. RTL
• B. DTL
• C. TTL
• D. CMOS

Hint:

CMOS technology is the foundation of modern microprocessors and battery-operated devices.
Its near-zero static power consumption makes it highly scalable and thermally manageable.
Remember: CMOS $\rightarrow$ Lowest static power dissipation.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The question asks to identify which of the given semiconductor logic families (RTL, DTL, TTL, or CMOS) exhibits the lowest power dissipation.

Step 2: Detailed Explanation:

• Let us review the logic families listed:
- RTL (Resistor-Transistor Logic): An early bipolar family that consumes high static power due to current flow through resistors in the collector paths.
- DTL (Diode-Transistor Logic): Improved upon RTL but still relies on bipolar junctions and resistors, leading to significant static power dissipation.
- TTL (Transistor-Transistor Logic): Fast and widely used, but draws continuous current in its steady states.
- CMOS (Complementary Metal-Oxide-Semiconductor): Uses complementary pairs of p-type and n-type MOSFETs.

• In any static state (logic high or logic low), one of the transistors in the CMOS complementary pair is completely turned OFF.

• Because one transistor is always non-conducting, there is no direct low-resistance path from the supply voltage (\( V_{DD} \)) to ground.

• As a result, the static power dissipation of CMOS circuits is extremely low, limited only by negligible junction leakage currents (typically in the nanowatt range).

• Power is primarily dissipated only during switching transitions (dynamic power) when charging and discharging capacitive loads. This makes CMOS the family with the lowest overall power dissipation.