Consider the current-to-voltage converter shown in figure 6.7. Applying our ideal amplifier rules gives
Figure 6.7: Current-to-voltage converter.
Therefore 
and the circuit acts as a
current-to-voltage converter.
Figure 6.8 shows several current sources driving the negative input of an inverting amplifier. Summing the current into the node gives
Figure 6.8: Current summing amplifier.
Therefore
If 
, we have
and the output voltage is proportional to the sum of the input voltages.
For only one input and a constant reference voltage
where the second term represents an offset voltage. This provides a convenient method for obtaining an output signal with any required voltage offset.