The following circuit amplifies a
voltage by a factor (R1 / R2).
What is important in this circuit is that it amplifies by
almost exactly (-R1 /R2) so
that the gain of the circuit can be controlled precisely by
controlling the resistor values precisely.
Inverting amplifier

Inverts and amplifies a voltage (multiplies by a negative
constant)
-

- Zin = Rin
(because V −
is a virtual ground)
- A third resistor, of value
,
added between the non-inverting input and ground, while not
necessary, minimizes errors due to input bias currents.
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