Propagation delay vs. maximum operating frequency As the propagation delay of a digital logic family increases, what happens to its maximum usable clock frequency?

Introduction / Context:
Propagation delay determines how quickly a logic signal traverses from input to output. System clock rates must respect these delays with adequate margin, making the relationship between delay and maximum frequency fundamental to timing design and static timing analysis.

Given Data / Assumptions:

• Propagation delay (tpd) is the time from a valid input transition to a valid output transition.
• Maximum frequency is limited by the slowest path delay in the clocked data path.
• Setup/hold and contamination delays are respected, but focus is on the basic inverse relation.

Concept / Approach:

In synchronous systems, the clock period must exceed the sum of logic propagation delays and register setup times. As propagation delay gets larger, the minimum safe clock period increases, which directly lowers the maximum clock frequency (fmax = 1 / Tmin).

Step-by-Step Solution:

Verification / Alternative check:

Empirical observation across logic families: ECL (short delays) allows high frequencies; older standard TTL or CMOS with larger delays supports lower fmax, confirming the inverse relationship.

Why Other Options Are Wrong:

• Higher maximum frequency: contradicts the inverse relation.
• Maximum frequency unaffected: ignores timing reality.
• Minimum frequency unaffected: minimum frequency is generally not the limiting factor in synchronous logic; maximum frequency is.

Common Pitfalls:

• Ignoring routing/interconnect delay, which also contributes to Tpath.
• Forgetting to include setup time and clock skew in the timing budget.

Final Answer:

lower the maximum frequency