Flip-flop timing parameters: Which parameters specify the propagation delay from the clock (Cp) input to the Q output?

Difficulty: Easy

Correct Answer: tPHL, tPLH

Explanation:


Introduction / Context:
Datasheets list several timing parameters for sequential devices. Correctly identifying propagation delays from clock to output is essential for timing closure and performance prediction.


Given Data / Assumptions:

  • Edge-triggered flip-flops with defined delays.
  • tPHL and tPLH denote propagation from input to output with polarity.
  • Other parameters include setup/hold, pulse width, and maximum frequency.


Concept / Approach:
Propagation delay measures time for an output transition after a triggering input event. For clocked devices, the relevant labels are tPLH (LOW-to-HIGH at output) and tPHL (HIGH-to-LOW at output) after a defined clock edge.


Step-by-Step Solution:

1) Identify the cause: active clock edge at Cp.2) Map to effects: Q transitions occur after a delay.3) Read tPLH/tPHL as the delays for the two transition polarities.


Verification / Alternative check:
Scope measurements of Q relative to Cp confirm datasheet values within tolerances.


Why Other Options Are Wrong:

  • ts, th: Setup and hold requirements, not propagation delay.
  • tw(L), tw(H): Minimum pulse widths, not output delays.
  • fmax: Maximum toggling frequency, a derived bound, not a delay parameter.


Common Pitfalls:
Confusing tpd with setup/hold and ignoring process/voltage/temperature effects on delays.


Final Answer:
tPHL, tPLH

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