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?


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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
  • \$\begingroup\$ And yes, I have no answer to your first part of the question - this is only for the second part ;) \$\endgroup\$
    – Jontas
    Commented May 19, 2012 at 11:16
  • \$\begingroup\$ I understand where slew rate comes from in VFA's, but how come that CFA's has 'Essentially unlimited slew rate'? \$\endgroup\$
    – jippie
    Commented May 20, 2012 at 8:52

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