You may be able to achieve lower phase delay by using an opamp that is not fully compensated for unity gain (e.g. it may only be stable for gains > 10); whether a suitable opamp (low noise, low offset, etc) exists, I do not know. You might start by looking at the LT1226. Alternatively, you could construct your own opamp (not a trivial project when high frequency performance is involved). Finally, you might find advice by searching the web for articles about wideband amps, oscilloscope amps, and similar. If the current sense resistor is not grounded, then common-mode response will also become relevant. If the current sense signal is not sinusoidal and/or has a varying frequency, then acceptable performance at one frequency will not guarantee acceptable performance at other frequencies.I want to measure the current through a device, which has to be in phase with the voltage generated in another part of the circuit (to get the current-voltage relation, like a curve tracer).