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