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Propagation delay in flip flops is the time taken for a change in input to affect the output. It is an important parameter in digital circuit design, affecting the overall speed and performance of the system. This guide provides a clear, step-by-step process to calculate propagation delay in flip flops.
Understanding Propagation Delay
Propagation delay is typically measured from the clock edge to the point where the output stabilizes after a change in input. It is usually divided into two components: tPLH (propagation delay for a low-to-high transition) and tPHL (propagation delay for a high-to-low transition).
Steps to Calculate Propagation Delay
- Identify the relevant parameters: Obtain the flip flop’s datasheet to find tPLH and tPHL.
- Apply input change: Introduce a known input transition and observe the output response.
- Measure the delay: Record the time difference between the clock edge and the output reaching 50% of its final value.
- Calculate average delay: For a more accurate measure, average tPLH and tPHL if both are available.
Example Calculation
Suppose a flip flop has tPLH of 10 ns and tPHL of 12 ns. The average propagation delay is calculated as:
Propagation Delay = (tPLH + tPHL) / 2 = (10 ns + 12 ns) / 2 = 11 ns