What's a current feedback amplifier?

Question

Another opamp question. Most opamps seem to be voltage feedback amplifiers (VFA), but there also seem to be current feedback amplifiers (CFA). When would you use a CFA, and what are their (dis/)advantages?

Answer 1

If you have not yet read Voltage feedback vs. current feedback amplifiers: Advantages and limitations by Xavier Ramus I would recommend that, it is both nice and in depth on this subject

Classical Advantages of Voltage Feedback Op Amps

• Typically can deliver better DC accuracy
  • This is most applicable to pulse oriented signal requirements - typically, DC precision is less important in AC coupled (communications) channels
• Can be the lowest overall equivalent input noise
  • Best noise (< 1.2nV/√Hz) comes at the price of high quiescent current and non-unity gain stability.
• Typically internally compensated. Note that some external compensation VFB exist.
• The highest accuracy, lower noise devices also have a typical architecture, limiting the maximum achievable slew rate.
• Low noise Transimpedance application are ideal target application

Classical Advantages of Current Feedback Op Amps

• Essentially unlimited slew rate - gives very high full power bandwidth
  • Most data sheet slew rate numbers are either limited by the input stage buffer or are actually reporting bandwidth limited rise time by mistake
• Nearly gain bandwidth independent
  • Most useful aspect of this is intrinsic low gain stability with very high closed loop BW
• Most CFB also provide a large output current drive capability.
• Application such as adder and high gain application are ideal target application