summing amplifier

This is a Current-Controlled Current Source using an operational amplifier, the output is delivered to a grounded load. The output/load current is equal to the current that flows through the feedback resistance to the noninverting terminal, Iload = Ifp. The current through Rfp is equal to the voltage across it divided by its resistance, Iload = Ifp = Vfp / Rfp. The voltage across Rfp is equal to the voltage drop across the feedback resistance to the inverting terminal, Iload = Ifp = Vfp / Rfp = (Vfn) / Rfp. The voltage drop across Rfn is equal to the the current through it multiplied by its resistance Iload = Ifp = Vfp / Rfp = [(Ifn)(Rfn)] / Rfp. The current through Rfn is equal to the input current Iin, Iload = Ifp = Vfp / Rfp = [(Iin)( Rfn)] / Rfp. The output current is simply the input current scaled by the ratio of the feedback resistances to the inverting and noninverting terminals, Iload = ( Rfn / Rfp) (Iin).