Match the amplifier types to their characteristic frequency responses: (A) RC-coupled amplifier, (B) Tuned amplifier, (C) Chopper-stabilized amplifier, (D) DC amplifier — with: (1) Very low drift, (2) Flat response from 0 Hz onward, (3) Flat response with lower and upper cutoff, (4) Peaked gain at resonance.

Introduction / Context:
Different amplifier configurations serve different spectral needs. Recognizing how their frequency responses look (flat band, cutoffs, resonance, drift performance) is crucial for audio, RF, and precision DC applications. This question pairs four common amplifier classes with their signature frequency-response traits.

Given Data / Assumptions:

• (A) RC-coupled amplifier
• (B) Tuned amplifier
• (C) Chopper-stabilized amplifier
• (D) DC amplifier
• Candidate traits: (1) very low drift, (2) flat from 0 Hz, (3) flat with finite passband and cutoffs, (4) resonant peak

Concept / Approach:

RC-coupled stages (e.g., common-emitter with coupling/bypass capacitors) exhibit a mid-band region of nearly flat gain bounded by low- and high-frequency cutoffs. Tuned amplifiers include frequency-selective LC tanks, giving a peaked response at resonance (high Q → narrowband). Chopper-stabilized amplifiers up-convert DC/low-frequency signals, amplify, and demodulate to achieve ultra-low offset and drift. True DC amplifiers pass down to 0 Hz (no coupling caps), so their passband includes DC.

Step-by-Step Solution:

Verification / Alternative check:

Bode plots and standard small-signal models confirm these shapes: single-pole high/low-cutoff for RC, band-pass with resonance for tuned LC, and flat-to-DC for DC amplifiers.

Why Other Options Are Wrong:

Swapping (2) and (3) mixes DC capability with AC-coupled behavior; assigning (4) to RC ignores the absence of a tuned tank.

Common Pitfalls:

Assuming “flat” always means DC-to-∞; forgetting that coupling capacitors exclude 0 Hz; conflating chopper stabilization with simple auto-zeroing without drift benefits.

Final Answer:

A-3, B-4, C-1, D-2