Question

Which of the following type of noise becomes of great importance at high frequencies?

• A. Short noise
• B. Random noise
• C. Impulse noise
• D. Transit-time noise

Hint:

Transit-time noise dominates at high frequencies due to charge carriers taking finite time to cross semiconductor regions.

Answer 1

The Correct Option is D

At high frequencies, particularly in microwave and RF applications, transit-time noise becomes significant. This type of noise arises due to the finite time it takes for charge carriers (electrons or holes) to traverse the active region of a device.
How does it arise?
As frequency increases, the time available per cycle decreases.
If the carrier transit time becomes comparable to the signal period, random fluctuations in transit time cause signal distortion.
Why is it prominent at high frequencies?
At lower frequencies, the transit time is negligible compared to the signal period.
But at high frequencies, the small differences in transit time cause significant phase and amplitude fluctuations—manifesting as noise.
Incorrect Options:
Short noise: Non-standard term.
Random noise: General term, not specific to frequency.
Impulse noise: Due to switching, not dominant at high frequencies.
Final Answer: (4) Transit-time noise