Analog and electronic circuits

Which correctly describes the idea of dominant-pole compensation used in op-amps?

  1. AGather all poles at the same frequency
  2. BMake the gain 0 dB at all frequencies
  3. CPlace one pole at a sufficiently low frequency so the gain falls below unity before reaching the other poles, ensuring stability
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Answer: C. Place one pole at a sufficiently low frequency so the gain falls below unity before reaching the other poles, ensuring stability

Dominant-pole compensation adds a capacitor to move one pole to a sufficiently low frequency. The gain then falls at −20 dB/decade from low frequencies and drops below unity (0 dB) before the other poles cause large phase shifts, giving sufficient phase margin so the amplifier is unlikely to oscillate under negative feedback.

  • A. Gathering poles at the same frequency makes the phase turn sharply and worsens stability.
  • B. Making the gain 0 dB at all frequencies would make the amplifier useless.
  • C. Correct. A dominant pole reduces the gain early to ensure stability.
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