Question
What is the term for the frequency at which the grounded-base current gain of a bipolar junction transistor has decreased to 0.7 of the gain obtainable at 1 kHz?
Answer Options
- A) Corner frequency
- B) Alpha rejection frequency
- C) Beta cutoff frequency
- D) Alpha cutoff frequency
Correct Answer: D
Explanation
The term alpha (\alpha) is the current gain of a Bipolar Junction Transistor (BJT) when configured in the grounded-base configuration (\alpha = I_C / I_E). All transistors have frequency limitations; as the operating frequency increases, the internal current gain begins to roll off due to internal junction capacitances and charge storage times.
Alpha cutoff frequency (f_T) is the standardized term for the frequency at which the grounded-base current gain (\alpha) has decreased to 0.707 (or -3 \text{ dB}) of the low-frequency gain (typically measured at 1 \text{ kHz}). This metric is crucial for determining the transistor’s maximum useful frequency for RF amplification.
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