Hi,
I've been trying to test my design using the OPA857 by injecting current from an ideal current source into the IN pin of the OPA857. However, whenever the probe for injecting current touches the net that connects to the IN pin, the output of the OPA857 begins to oscillate, presumably due to the parasitic capacitance introduced by the probe. I've tried adding a Cf capacitor and this seemed to help reduce the peak-to-peak level of the oscillations, but even with Cf=180pF the oscillations were still present. So instead I added a 100k resistor in series with the probe to isolate the capacitance of the probe from the IN pin of the OPA857 (i.e probe --> 100k --> IN pin of OPA857). With this approach, the oscillations went away completely the output of the OPA857 varied correctly in response to varying the injected current from 0uA to 60uA. Is this a valid way to test the OPA857? Obviously the 100k won't be part of the actual circuit, but it seems like it should be OK to use for the sole purpose of isolating the probe's capacitance.
Thanks,
James
