CMOS vs. TTL — identify a disadvantage of CMOS compared to TTL (classic families) In traditional comparisons at similar supply voltages, which is a disadvantage of CMOS relative to TTL?

Introduction / Context:
Comparing classic CMOS and TTL logic families helps designers choose parts for speed, power, and integration. Historically, CMOS offered dramatic static power savings but at a cost in switching speed versus the fastest TTL families of the same era and voltage range.

Given Data / Assumptions:

• Comparison refers to traditional 5 V logic families (e.g., 74HC/HCT vs 74F/74ALS).
• Modern advanced CMOS can be very fast, but the question concerns the classic generalization.

Concept / Approach:
CMOS uses complementary MOSFETs; static power is near zero except during transitions. TTL is bipolar and consumes more static power, but some TTL subfamilies (e.g., 74F) achieved very high speed. Thus, a standard textbook disadvantage of CMOS is lower switching speed compared to the fastest TTL, especially at older process nodes.

Step-by-Step Solution:
Identify traits: CMOS → low static power, high input impedance; TTL → faster in classic families.Eliminate benefits: “uses less power” and “smaller” are advantages of CMOS, not disadvantages.Choose “It switches slower.” as the disadvantage.

Verification / Alternative check:
Datasheet propagation delays: typical 74HC at 5 V often has tens of nanoseconds, while 74F TTL can be single-digit nanoseconds. This supports the general statement.

Why Other Options Are Wrong:

• It uses less power: that is a CMOS advantage.
• It is smaller: CMOS integration scales well; also an advantage.
• cost: context-dependent, not an inherent technology disadvantage.

Common Pitfalls:

• Projecting modern submicron CMOS speeds onto classic 5 V logic comparisons.
• Ignoring that HCT is pin-compatible with TTL levels but still CMOS internally.

Final Answer:
It switches slower.