BJT operating conditions (active region) Which statement correctly describes a Bipolar Junction Transistor (BJT) in its forward-active region?

Introduction / Context:
Understanding BJT biasing is fundamental for analog amplifiers and switching applications. The forward-active region is the usual operating region for linear amplification.

Given Data / Assumptions:

• NPN or PNP BJT used in common configurations (CE, CB, CC).
• Forward-active region biasing.
• Neglecting second-order effects like Early effect for the basic statement.

Concept / Approach:
In forward-active region, the emitter–base junction is forward biased to inject carriers from emitter into base, while the collector–base junction is reverse biased to sweep these carriers into the collector. This yields collector current approximately IC ≈ β * IB (or IC ≈ α * IE) with moderate dependence on VCE (Early effect).

Step-by-Step Solution:
Set VBE ≈ 0.7 V (Si) to forward bias E–B junction.Maintain C–B junction reverse biased (VCB > 0 for NPN).Carriers injected from emitter traverse thin, lightly doped base and are collected by the reverse field at C–B junction.Hence, option describing “E–B forward, C–B reverse” is correct.

Verification / Alternative check:
Small-signal hybrid-π models and textbook biasing diagrams reflect this junction polarity in forward-active operation.

Why Other Options Are Wrong:

• (b) ignores the Early effect; dependence is small but not zero.
• (c) BJTs are bipolar devices; minority carrier storage is central.
• (d) Emitter is heavily doped (for high injection efficiency); base is lightly doped and very thin.
• (e) Both junctions forward-biased corresponds to saturation, not active region.

Common Pitfalls:

• Confusing active region with saturation region.
• Assuming perfect independence of IC from VCE.

Final Answer:
The emitter–base junction is forward biased, and the collector–base junction is reverse biased