Circuit 03: Variable Input from 0 to 1.25 V

In this circuit, we will add a potentiometer to the circuit_01.
It will allow us to vary the input voltage at SIG between 0 V and 1.25 V

We have to make sure that the voltage at the SIG input does not exceed 1.25 V.
The voltage at the point between R1 ad R_POT is at maximum when the potentiometer is at the maximum value.
In that case:

which leads to the equation for the minimal R1: With the desired and easily available trimpot of value gives a minimum value for R1