Which statement best describes the effect of the Early effect on ro and gain in a BJT amplifier?

• A. The Early effect has no practical impact on amplifier design.
• B. It causes ro to be finite and makes gain depend on Vce.
• C. It only affects reverse leakage currents.
• D. It makes Ic perfectly constant with Vce.

Answer: (B)

The Early effect is the modulation of the base width by the reverse-biased collector-base junction, which makes the collector current depend slightly on the collector-emitter voltage even when the base current is fixed. In small-signal terms this shows up as a finite output resistance ro and as a change in gm with Ic as Vce changes. Since a common-emitter stage has gain roughly Av ≈ -gm (RC || ro), a finite ro and the fact that Ic (and thus gm) depends on Vce means the amplifier’s gain isn’t constant but changes with Vce. As Vce increases, Ic nudges upward due to base-width modulation, gm increases, and ro decreases slightly (ro ≈ VA/Ic), altering the overall gain. The statement is the best description because it directly ties ro becoming finite to the dependence of gain on Vce. The other options ignore the practical impact of ro, the dependence of Ic on Vce, or the nonzero ro.