For normal (active-region) operation of a bipolar junction transistor (BJT), the collector–base junction must be biased in which way?

Introduction / Context:
Transistor regions of operation (cutoff, active, saturation) are determined by the biases of the emitter–base and collector–base junctions. In amplifiers, BJTs are typically used in the forward-active region to provide linear gain.

Given Data / Assumptions:

• BJT intended for linear amplification (active region).
• Emitter–base junction is forward-biased.
• Collector–base junction bias determines region along with the base–emitter bias.

Concept / Approach:
In forward-active operation: base–emitter is forward-biased to inject carriers, and collector–base is reverse-biased to sweep carriers into the collector. This separation allows the collector current to be controlled by base current (or base–emitter voltage) with minimal dependency on collector–emitter voltage in the active region.

Step-by-Step Solution:
Set V_BE forward (about 0.7 V for silicon) to allow injection from emitter to base.Set collector–base junction reverse: this widens the depletion region and pulls carriers across.Observe transistor acts as a controlled current source in the active region.

Verification / Alternative check:
Device I–V curves show a relatively flat I_C versus V_CE in active mode when C–B is reverse-biased, compared to saturation where both junctions are forward-biased and gain collapses.

Why Other Options Are Wrong:
Forward-biased: would push device toward saturation, not linear amplification.Nonconducting/open: bias is an electrical condition, not merely an open circuit.Breakdown region: unsafe for normal operation; risks device damage.

Common Pitfalls:
Confusing saturation (both junctions forward) with active; assuming reverse bias implies no current—collector current still flows due to injected carriers.

Final Answer:
Reverse-biased