Introduction / Context:
Different logic families—DTL, TTL, ECL, and CMOS—have distinct trade-offs in speed, noise margins, fan-out, and power dissipation. Power efficiency is critical in battery-operated devices and large-scale integration. This question tests recognition of which family minimizes static power consumption.
Given Data / Assumptions:
- Logic families: DTL, TTL, ECL, and CMOS.
- Typical ambient conditions; nominal supply voltages.
- Focus on static (DC) power dissipation at logic 0/1, not dynamic at high switching rates.
Concept / Approach:
- CMOS (Complementary Metal-Oxide-Semiconductor) uses complementary pairs of MOSFETs.
- In steady states, one device of the pair is OFF, leading to near-zero DC current through the pull-up/pull-down path.
- Other families (TTL/DTL) maintain bias currents; ECL uses differential pairs with constant current, hence higher power.
Step-by-Step Solution:
Identify static power mechanism: CMOS → negligible static current; TTL/DTL → bias currents; ECL → constant tail current.Compare orders of magnitude: ECL (highest), TTL/DTL (moderate), CMOS (lowest in static).Conclude: Minimum static power dissipation → CMOS.
Verification / Alternative check:
Cross-check by considering battery devices and microcontrollers which overwhelmingly use CMOS due to low idle consumption.
Why Other Options Are Wrong:
- DTL: Diode-transistor logic still draws static current via biasing networks.
- TTL: Transistor-transistor logic consumes more static power than CMOS.
- ECL: Highest power due to constant current flow in differential pairs, traded for speed.
- None of the above: Incorrect because CMOS is correct.
Common Pitfalls:
- Confusing static with dynamic power; CMOS dynamic power can be significant at high frequencies (P ≈ C * V^2 * f).
- Assuming ECL is efficient because it is fast; speed does not imply low power.
Final Answer:
CMOS
Discussion & Comments