The circuit configuration shown on Picture 1 is called current to voltage converter. This configuration is closest to the inverting amplifier, only that resistor R1 is replaced with current source Is, which is actually the input signal for this circuit instead of the voltage input source Vi.
Picture 1: Current to voltage Converter
Since the current source Is can not flow into the amplifier's inverting input because of the high input resistance of the OA, it must flow through the resistor Rf. Since the inverting input is virtual ground, for the output voltage we can write:
Vo = -Is*Rf
So, according to this relation, the output voltage is always equal to -Is*Rf, no matter of the load resistance. That's why this circuit is called current to voltage converter. From the other side, the virtual ground assumption implies that Ri = 0, which is actually the input resistance of this circuit.
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