Oscillators and feedback amplifiers — match each item to its typical frequency range or impedance trait List I (Circuit) A. Wien bridge oscillator B. Voltage–shunt feedback amplifier C. Crystal oscillator D. Current–shunt feedback amplifier List II (Key characteristic) 1. Low output impedance 2. RF frequency range 3. Audio frequency range 4. High input impedance 5. High output impedance

Introduction / Context:
This matching problem checks recognition of classic oscillator types and feedback topologies against their hallmark operating ranges and impedance properties. Correctly pairing these helps with quick architecture selection in analog and RF design.

Given Data / Assumptions:

• Wien bridge oscillators are widely used for low-distortion audio-frequency generation.
• Voltage–shunt feedback takes a voltage sample from the output and mixes it in shunt at the input, tending to reduce output impedance.
• Crystal oscillators exploit quartz resonance and are commonly used at RF and high-stability HF/VHF.
• Current–shunt feedback samples output current and mixes in shunt at the input; current sampling raises output impedance.

Concept / Approach:
Map each item to the most engineer-relevant trait: Wien bridge → audio range; crystal → RF range; voltage–shunt feedback → low Z_out; current–shunt feedback → high Z_out due to current sampling (transresistance behavior).

Step-by-Step Solution:

Verification / Alternative check:
Feedback theory: shunt mixing at the input lowers input impedance; series mixing raises it. Current sampling (series at output) increases output impedance; voltage sampling (shunt at output) decreases it. Textbook oscillator chapters place Wien bridges in AF labs and crystals in RF frequency control.

Why Other Options Are Wrong:

• Swapping RF/AF ranges contradicts standard usage.
• Assigning high output impedance to voltage-shunt conflicts with voltage sampling at the output.
• Setting low output impedance for current-shunt mismatches current sampling behavior.

Common Pitfalls:
Confusing “series/shunt at input” with “voltage/current sampling at output.” Remember: voltage sampling → low Z_out; current sampling → high Z_out.

Final Answer:
A-3, B-1, C-2, D-5