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/âHz) 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
Jontas
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And yes, I have no answer to your first part of the question - this is only for the second part ;) â Jontas May 19 '12 at 11:16
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I understand where slew rate comes from in VFA's, but how come that CFA's has 'Essentially unlimited slew rate'? â jippie May 20 '12 at 08:52