In this circuit
the input voltage is applied to the
amplifier uses negative feedback to
is no difference in the voltage between the inverting and non-inverting
inputs, so we can say that the voltage at the non-inverting and the
inverting input is the same.So we can say that the voltage at P is
no current is drawn by the inverting input, the current in
is the same as the current in
So we can treat the two resistors as a potential
divider and apply the potential divider equation.
We can therefore write:
Vout/Vin is the gain.
can be rewritten
we look at the input, we see that there is no feedback resistor in the input,
therefore we can say that the input resistance is that of the op-amp.The input resistance is very high indeed, and very little current is
problem with the inverting amplifier used as a voltage
follower is that the output is at 180o out of phase with the
input.A voltage follower can be
based on the non inverting circuit with 100 % negative feedback to the inverting
input, and input resistance is very high indeed.
voltage gain of the op-amp in this configuration is about 1.This because ofthe feedback
factor (the fraction fed back), given the code
(beta, a Greek letter ‘b’)
can show this by considering the open
The actual gain
is given by:
b is 1, and
is very large, we can
main use of the voltage follower is as a buffer amplifier, which matches a high
input impedance with a low input load.You
would come across such a circuit in the input stage of a digital multimeter,
which has a very high input impedance, allowing the voltage read to be the same
as the voltage that should be there.