Fastest TTL-derived logic family (maximum clock frequency) Among the following logic families, which typically achieves the highest maximum clock frequency?

Introduction / Context:Classic TTL families evolved to improve speed and reduce power. Schottky clamping prevents deep saturation, improving switching time; later “Advanced Schottky” refinements push speed further. This question compares well-known TTL derivatives and HCMOS on maximum practical clock frequency (ignoring ECL, which is not listed here).

Given Data / Assumptions:

• S-TTL = Schottky TTL (74SXX).
• AS-TTL = Advanced Schottky (74ASXX), generally faster than 74SXX.
• HS-TTL = High-Speed TTL (74HXX), older and slower than Schottky variants.
• HCMOS = High-speed CMOS; fast, but in classic comparisons AS-TTL leads over HS-TTL and S-TTL.

Concept / Approach:Advanced Schottky TTL reduces storage delay and optimizes device structures/resistors for improved speed relative to earlier TTL lines. Although modern CMOS in deep-submicron processes is very fast, traditional family-to-family comparisons (same era) place 74ASXX at the top among the given TTL variants for max clock rate.

Step-by-Step Solution:

Verification / Alternative check:Historic datasheets show lower t_pd for 74AS vs. 74S and 74H series under comparable loading.

Why Other Options Are Wrong:

• A/C: S-TTL and HS-TTL are slower than Advanced Schottky.
• D: HCMOS speeds are application- and process-dependent; the classic comparison favors 74AS.

Common Pitfalls:Confusing modern high-speed CMOS ASICs or FPGAs with classic HCMOS logic families.

Final Answer:AS-TTL