BJT junction biasing sign convention: Does V_BE normally reverse-bias the base–emitter junction in a properly biased amplifier stage?

Introduction / Context:
Correct biasing of the base–emitter (B–E) junction is central to BJT operation. In forward-active operation, the B–E junction is forward-biased while the collector–base (C–B) junction is reverse-biased. Misstating the polarity of V_BE leads to confusion about conduction mechanisms, emitter injection, and small-signal parameters such as g_m.

Given Data / Assumptions:

• Linear amplifier bias (forward-active region).
• NPN example: base about 0.6–0.7 V above emitter at room temperature.
• PNP example has reversed polarities but still forward-biases the B–E junction.

Concept / Approach:
For conduction, the B–E junction must be forward biased so carriers inject from the emitter into the base. In an NPN, V_BE ≈ +0.7 V (base positive with respect to emitter). In a PNP, V_BE ≈ −0.7 V (base negative with respect to emitter). Either way, the magnitude biases the B–E junction forward, not reverse. Reverse biasing B–E would shut the device off (cutoff) except for small leakage currents.

Step-by-Step Solution:

Verification / Alternative check:
I–V curves and diode tests confirm that base–emitter behaves like a diode that must be forward biased for normal conduction.

Why Other Options Are Wrong:
Device polarity does not change the forward-bias requirement; cutoff and temperature do not invert the biasing rule.

Common Pitfalls:
Mixing up junction polarities between NPN and PNP; assuming the same sign conventions across reference points without care.

Final Answer:
Incorrect