The circuit configuration shown on Picture 1 is called voltage to current converter. This configuration is actually same as the inverting amplifier, but the difference here is that the output load is not connected to the ground, actually the output load here is resistor R2 from the inverting amplifier and it takes the place of the feedback resistor.
Picture 1: Voltage to current Converter
Since the inverting input is the virtual ground, the current that flows through the resistor R1 is the same as the current that flows through the load Rl. Just to mention here, the load can have different nature, it can be from pure resistance nature or it can have more complex nature - impedance. So, according to the conditions in this circuit, we can write:
Il = Ii = Vi/R1
As we can see from this relation, the load current is always Vi/R1, no matter of the load resistance. That's why this circuit is called voltage to current converter.
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