Basic Op Amp circuits

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Buffer Amplifier

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Buffer Amplifier

Used to transfer voltage but not current to the following circuit. This amplifier can be used to negate the loading effects. No current flows through the amplifier, thus there is no voltage drop through the input resistor (going to the buffer amplifier).

Inverting Amplifier

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Inverting Amplifier

Uses negative feedback to invert and amplify voltage. Using nodal analysis at the negative terminal, the gain is found to be $- \frac{R_{2}}{R_{1}}$
$R_{b i a s} = \frac{R_{1} R_{2}}{R_{1} + R_{2}}$
To get rid of unwanted DC components, a capacitor can be added inbetween $R_{1}$ and $V_{i n}$ . In this case $R_{b i a s} = R_{2}$

Summing Amplifier

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Summing Amplifier

$V_{o} = - R_{f} (\frac{V_{3}}{R_{3}} + \frac{V_{2}}{R_{2}} + \frac{V_{1}}{R_{1}})$
If all resistances are equal, then the output voltage is the (negative) sum of the input voltages
$\frac{1}{R_{b i a s}} = \frac{1}{R_{1}} + \frac{1}{R_{2}} + \frac{1}{R_{3}} + \frac{1}{R_{f}}$

Noninverting Amplifier

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Noninverting Amplifier

$V_{o} = V_{i n} (1 + \frac{R_{2}}{R_{1}})$
$R_{b i a s} = \frac{R_{1} R_{2}}{R_{1} + R_{2}}$
$R_{b i a s}$ goes between the positive terminal and $V_{i n}$
To get rid of unwanted DC components, a capacitor can be added inbetween the positive terminal and $V_{i n}$ . The bias resistor has the same value, and is placed inbetween the positive input terminal and ground.

Differential Amplifier

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Differential Amplifier

$V_{o} = V_{2} \frac{(R_{1} + R_{f}) R_{g}}{(R_{2} + R_{g}) R_{1}} - V_{1} \frac{R_{f}}{R_{1}}$
If you let $R_{1} = R_{2}$ and $R_{g} = R_{f}$ then the equation simplifies to $V_{o} = \frac{R_{f}}{R_{1}} (V_{2} - V_{1})$

Possible circuits to add in the future

Voltage-to-current converter
Current-to-voltage converter
Current amplifier
Integrator
Differentiator

Reviewers

Victor Shepherd
Michael Vier

Readers

Christopher Garrison Lau I

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