Think of the Early Effect as the collector "reaching into" the base. A larger reverse voltage on the collector gives it a longer "reach" (wider depletion region), which makes the base effectively narrower.
Step 1: Define the Early Effect.
The Early effect, also known as base-width modulation, is the variation of the effective width of the base in a Bipolar Junction Transistor (BJT) due to a change in the collector-base junction voltage. This change in base width affects the collector current and the transistor's output characteristics.
Step 2: Analyze the collector-base junction.
In the active region of operation, the collector-base junction is reverse-biased. This creates a depletion region at the junction.
Step 3: Connect reverse bias to base width.
As the reverse bias voltage across the collector-base junction increases, the width of this depletion region increases. Since the depletion region extends into both the collector and the base, an increase in its width causes the effective (or neutral) width of the base region to decrease. This is the mechanism of the Early effect. Therefore, it is caused by the collector-base reverse bias.
