BJT Amplifier Configurations vs. Key Characteristics Match each bipolar transistor configuration to its most typical small-signal characteristics.
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AA-1, B-2, C-3
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BA-1, B-2, C-3
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CA-3, B-1, C-2
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DA-3, B-2, C-1
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EA-2, B-1, C-3
Answer
Correct Answer: A-1, B-2, C-3
Explanation
Introduction / Context:BJT amplifiers are commonly implemented in three configurations: common emitter (CE), common collector (CC, emitter follower), and common base (CB). Each has distinctive voltage and current gain properties important for stage selection in analog design.
Given Data / Assumptions:
- CE: general-purpose gain stage.
- CC: buffer with high input and low output impedance.
- CB: wide bandwidth, low input impedance stage.
Concept / Approach:
Rules of thumb: CE provides both significant voltage and current gain; CC has voltage gain slightly less than 1 but high current gain; CB exhibits current gain less than 1 but high voltage gain. These patterns guide the matching directly.
Step-by-Step Solution:
CE → good voltage gain, good current gain ⇒ A-1.CC → voltage gain < 1, high current gain ⇒ B-2.CB → current gain < 1, voltage gain high ⇒ C-3.Verification / Alternative check:
Small-signal hybrid-pi models or gm*r_o approximations reproduce these qualitative results, confirming the mapping.
Why Other Options Are Wrong:
Swapped pairings contradict core behavior: CC cannot provide voltage gain > 1; CB cannot provide current gain > 1 under typical bias conditions.
Common Pitfalls:
Confusing CC with CE because both can show strong current gain; overlooking that CC is primarily a buffer.
Final Answer:
A-1, B-2, C-3