# Designing a non-inverting amplifier with a gain of 2

Quetion:

Design a noninverting amplifier with a gain of 2. At the maximum output voltage of 10 V the current in the voltage divider is to be 10 μA.

I can easily understand the first part of the problem . Here, gain = 1+$\frac{R_f}{R_1}$ , To make gain = 2, $R_1$ should be same as $R_f$
But what is meant by current in the voltage divider in the second part of the question?

But what is meant by current in the voltage divider in the second part of the question?

It's a hint as to what value resistors to use. With 10 volts and 10 uA, the impedance is 1 million ohms hence, R1 = Rf = 500 kohm.

But what is meant by current in the voltage divider in the second part of the question?

This question is to determine sensible resistor values for Rf and R1. For a gain of 2 they could both be 100 Ω or both be 1 MΩ but different currents will result and it is unlikely that your op-amp could maintain 10 V output in the 100 Ω case. In the 1 MΩ case it might be a bit sensitive to noise or bias currents may cause too much of an offset.

• You know the output voltage (10 V) and you know that the left side of R1 is connected to ground (although the schematic is missing a connection dot).
• You know the current.
• Now calculate the total resistance (Rf + R1).

You should be able to figure it out from there.