In voltage mode operation,the impedance(R parallel C) of a node will decrease as the signal freq increases with the current(I) flowing through unchanged.So according to V=ZI,the voltage at that node is degraded 3dB/dec at the signal freq at 1/RC.(assume the node has domonant pole)

But how about the analysis of current mode circuit?How to define the BW of a current mode circuit(EX:current conveyor,CFA)?Does a current amp have BW?
(My partner says that the BW of a current mode circuit is unit gain bandwidth,but I don't understand)

 

A current-mode op amp does have a bandwidth as defined in its data sheet but it's not greatly affected by the closed-loop gain so it doesn't have a gain-bandwidth product value like a voltage-mode op amp.
That's because a current-mode op amp doesn't require the single-pole internal roll-off for compensation that a voltage-mode op amp does.

Incidentally a single-pole RC circuit has a voltage rolloff of 6dB/octave or 20dB/decade , not 3dB.

 

Good info on current feedback amplifiers is found here. https://en.wikipedia.org/wiki/Current-feedback_operational_amplifier