Propagation Delay Definitions — tPLH Measurement For a synchronous flip-flop, propagation delay time tPLH is measured from which reference to which output transition?
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Atriggering edge of the clock pulse to the LOW-to-HIGH transition of the output
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Btriggering edge of the clock pulse to the HIGH-to-LOW transition of the output
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Cpreset input to the LOW-to-HIGH transition of the output
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Dclear input to the HIGH-to-LOW transition of the output
Answer
Correct Answer: triggering edge of the clock pulse to the LOW-to-HIGH transition of the output
Explanation
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