inverting amplifier configuration (A-level only) Flashcards – AQA A-level Physics (7408)

How are the input resistor, feedback resistor and non-inverting input connected in an inverting amplifier?

• $R_{\mathrm{in}}$ connects the input voltage to the inverting input.
• $R_{\mathrm{f}}$ connects the output to the inverting input.
• The non-inverting input is connected to earth.

Why is the inverting input of an inverting amplifier called a virtual earth?

Negative feedback keeps it approximately at zero potential.

Why are the currents through the input and feedback resistors equal in an ideal inverting amplifier?

No current enters the operational amplifier input.

In an ideal inverting amplifier, what are the two expressions for the resistor current $I$, taken as positive towards the virtual-earth node through the input resistor?

$I=\frac{V_{\mathrm{in}}}{R_{\mathrm{in}}}$ and $I=\frac{0-V_{\mathrm{out}}}{R_{\mathrm{f}}}$.

What is the voltage gain of an inverting amplifier in terms of its input and feedback resistances?

$\frac{V_{\mathrm{out}}}{V_{\mathrm{in}}}=-\frac{R_{\mathrm{f}}}{R_{\mathrm{in}}}$

What does the negative voltage gain of an inverting amplifier indicate?

The output has the opposite polarity to the input.

Under what operating condition does the inverting-amplifier gain equation apply?

When negative feedback maintains linear operation, rather than when the output is saturated.