Propagation Delay Definitions — tPLH Measurement For a synchronous flip-flop, propagation delay time tPLH is measured from which reference to which output transition?

Introduction / Context:
Datasheets specify separate propagation delays for LOW-to-HIGH and HIGH-to-LOW output transitions. Correct interpretation of tPLH and tPHL ensures accurate timing analysis and setup of constraints in synchronous designs.

Given Data / Assumptions:

• tPLH refers to the output transition from LOW to HIGH.
• Trigger reference is the active clock edge for edge-triggered devices.
• Asynchronous preset/clear are measured separately and are not part of tPLH unless explicitly stated.

Concept / Approach:
By definition, tPLH is the time from the specified input transition (usually the triggering clock edge) to the resulting LOW-to-HIGH transition at the output pin under given load and supply conditions.

Step-by-Step Solution:
Identify the input event: the triggering clock edge.Identify the output event: Q transitions from LOW to HIGH.Measure the time difference under specified conditions: that interval is tPLH.

Verification / Alternative check:
Open any logic family datasheet: tPLH and tPHL are listed separately with distinct typical and maximum values.

Why Other Options Are Wrong:

• Clock to HIGH-to-LOW transition: That is tPHL.
• Preset or clear references: Those are asynchronous timing specs, not the synchronous tPLH definition.

Common Pitfalls:
Swapping tPLH and tPHL; mixing asynchronous and synchronous timing definitions.

Final Answer:
triggering edge of the clock pulse to the LOW-to-HIGH transition of the output