A very simple analysis can put the operation of the AD8001, acurrent feedback amplifier, in familiar terms. Being a currentfeedback amplifier, the AD8001’s open-loop behavior is expressedas transimpedance, ΔVO/ΔI–IN, or TZ. The open-loop transimpedancebehaves just as the open-loop voltage gain of a voltagefeedback amplifier, that is, it has a large dc value and decreasesat roughly 6 dB/octave in frequency.Since the RIN is proportional to 1/gM, the equivalent voltagegain is just TZ × gM, where the gM in question is the transconductanceof the input stage. This results in a low open-loopinput impedance at the inverting input, a now familiar result.Using this amplifier as a follower with gain, Figure 4, basicanalysis yields the following result.