CMOS vs. TTL power at low supply Compared at a 3 V supply, a CMOS logic IC will typically consume how much power relative to a TTL IC?

Introduction / Context:
Choosing between logic families involves trade-offs in speed, power, and noise immunity. CMOS devices are renowned for very low static power, especially at reduced supply voltages, making them ideal for battery-powered and portable applications.

Given Data / Assumptions:

• Supply voltage under consideration: approximately 3 V.
• Comparing standard CMOS (e.g., 74HC/74HCT/4000B families) to classic TTL families.
• Static (quiescent) and dynamic power trends are considered qualitatively.

Concept / Approach:

CMOS power is roughly proportional to C_load * V^2 * f for dynamic switching, and its static current is extremely small (leakage). TTL draws appreciable static bias current even when not switching, and is not specified to operate at 3 V in many variants. Consequently, at low supply voltages, CMOS typically consumes substantially less power than TTL for similar tasks.

Step-by-Step Reasoning:

Verification / Alternative check:

Datasheets list ICC for CMOS in microamps at low VDD, while TTL families (e.g., 74LS) show milliamps even at 5 V, and typically do not operate at 3 V. This confirms the qualitative comparison.

Why Other Options Are Wrong:

• “More power/the same/no power” contradict core device physics and datasheet values.

Common Pitfalls:

• Ignoring frequency dependence; while CMOS dynamic power rises with frequency, at equal operating points it remains lower than TTL at low VDD.

Final Answer:

less power than a TTL IC