Chapter 13 - Review of Current Feedback Operational Amplifiers

Abstract

Current feedback operational amplifiers are devices where the main feedback path from output to input carries a current, and not a voltage, as in voltage feedback op-amps. Current feedback op-amps do not suffer from the gain bandwidth product paradigm as do voltage feedback operational amplifiers, and can achieve very high bandwidths. However, they do have other limitations. In a conventional operational amplifier, a compensating capacitor is used to tailor the open-loop frequency response so that it is dominated by a single pole. In a conventional internally compensated op-amp there is a compensating capacitor internal to the device. The basic current-feedback op-amp differs from the conventional voltage-feedback op-amp in several respects. The negative input has very low input impedance (by design), since this negative node is the place where the back current is fed. The current feedback op-amp does not have the same slew rate limit as in a conventional voltage-feedback op-amp. A more detailed model of the current-feedback op-amp, modeling some further effects that may affect bandwidth, gain, and stability are illustrated in this chapter.