Amplifier topologies — match each circuit name to its hallmark characteristic List I A. Darlington amplifier B. Common-base (CB) amplifier C. Cascode amplifier D. Complementary-symmetry amplifier List II 1. A circuit using pnp and npn transistors 2. A CS stage driving a CG (or CE driving CB) — high gain, wide bandwidth 3. A circuit with overall voltage gain near 1 and very large input impedance 4. A circuit with low input impedance

Introduction / Context:Recognizing amplifier building blocks accelerates circuit analysis. Darlington, CB, cascode, and complementary-symmetry stages each have distinctive impedance and gain traits used throughout analog design.

Given Data / Assumptions:

• Darlington commonly used as an emitter follower pair: very high input impedance, near-unity voltage gain, high current gain.
• CB stage exhibits low input impedance and high bandwidth.
• Cascode (CE→CB or CS→CG) combines high gain with wide bandwidth and improved Miller effect.
• Complementary-symmetry uses both pnp and npn devices (e.g., push–pull output stages).

Concept / Approach:Map each named topology to the property engineers exploit in practice: input/output impedance behavior or device complementarity.

Step-by-Step Solution:

Verification / Alternative check:Textbooks and datasheets list CB input resistances of only a few ohms; Darlington emitter followers offer megaohm-range input; cascodes show extended bandwidth; complementary stages are standard in AB push–pull audio outputs.

Why Other Options Are Wrong:

• Swapping Darlington with CB confuses high versus low input impedance roles.
• Assigning “pnp + npn” to anything but complementary symmetry is incorrect.

Common Pitfalls:Assuming “cascode” is just two CE stages in series; the CB/CG upper device is crucial for bandwidth.

Final Answer:A-3, B-4, C-2, D-1