Signal edge realism: Evaluate the statement: “A digital pulse is not perfectly square; it requires finite time to rise from 0 to 1 and to fall from 1 to 0.”

Introduction / Context:
Ideal square waves have instantaneous transitions. Real digital circuits, however, exhibit finite rise and fall times due to device physics and parasitic capacitances. Recognizing this helps with timing analysis, signal integrity, and bandwidth considerations.

Given Data / Assumptions:

• Any physical driver has limited slew rate.
• Interconnects add capacitance and inductance.
• Loads present capacitance that must be charged/discharged.

Concept / Approach:
The rise time (tr) is commonly defined between 10% and 90% of the final value; fall time (tf) is similarly defined. Nonzero tr/tf means the waveform is not perfectly square and has finite spectral content, which affects ringing, overshoot, and EMI.

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