# How do we have a fixed current in this case?

If we are doing a current-to-voltage converter we can use negative feedback on a common-emitter configuration. Using npn transistors would look like so:

We are using a fixed current input and it forces the base-emitter voltage to be the corresponding value according to the Ebers Moll model. So my question is, how can we make the current input exactly what we want so it is mirrored on the other side?

I don't really know how it is possible to feed the exact current we want to the dual-transistors without having to calculate the voltage V1 in equilibrium for $I_c$.

If we increase $I_c$ then $V_{BE}$ would increase, which would make the voltage drop across $R_1$ to decrease (in a smaller amount). In order for the control of the current to be exact, when would need to calculate the precise increase we need in $V_1$ to reach the desired $I_c$ current so the base-emitter voltage is exactly what is needed to drive the second transistor. How can we keep the current exactly how we need it?