Assertion (A): An IMPATT diode can be used in both amplifiers and oscillators at microwave frequencies. Reason (R): An IMPATT diode works because it has a low resistance. Choose the correct relationship between A and R.

Introduction / Context:
IMPATT (Impact Avalanche Transit-Time) diodes are widely used for microwave generation and amplification. The principle relies on avalanche multiplication and carrier transit-time phase delay that together yield negative resistance at RF, enabling gain and oscillation. This item probes whether you can distinguish the true operating reason from an incorrect simplification.

Given Data / Assumptions:

• Device operates in avalanche mode with a drift region.
• Applications include oscillators (free-running or injection-locked) and amplifiers.
• Evaluation is about correctness and causality of A and R.

Concept / Approach:
IMPATT diodes exhibit negative differential resistance at microwave frequencies due to the combined phase shift from avalanche build-up and carrier transit delay. This negative resistance supports oscillations and provides gain in amplifier topologies. Merely having a “low resistance” does not explain these behaviors and is not the operative mechanism.

Step-by-Step Solution:

Verification / Alternative check:
Small-signal models show a negative real part of impedance in the intended frequency range; practical circuits bias for avalanche and tune for the desired frequency.

Why Other Options Are Wrong:

• Options implying R is correct contradict device physics.

Common Pitfalls:
Confusing negative resistance with merely small ohmic resistance; overlooking the role of impact ionization timing.

Final Answer:
A is correct but R is wrong