Operational Amplifier
A high-gain electronic voltage amplifier with a differential input and, usually, a single-ended output. An active circuit element. Voltage-controlled voltage source. Aka. op-amp.
- Has 2 inputs:
- Inverting input (-)
- Non-inverting input (+)
- Has 1 output
- 2 supply terminals (usually DC):
- Positive
- Negative
- Reference/ground
Uses
Can be used to perform a variety of operations on signals, such as:
- Amplification
- Addition
- Subtraction
- Multiplication
- Division
- Integration
- Differentiation
Gain
The ratio between the output and the difference between the input voltages.
Equivalent circuit
Here:
- Input resistance, very high - Output resistance, very low - Gain, ranges from to . - voltage difference between input terminals - voltage input, ranges between and
Ideal op-amp
- Infinite input impedance
- Zero output impedance
- Infinite gain for differential input signal
( ) - Infinite bandwidth
Summing-point constraint
The voltage at the inverting input terminal is equal to the voltage at the non-inverting input terminal.
Feedback types
Usually op-amp circuits are designed with feedback. A feedback is a connection from the output to the input of the op-amp.
Negative feedback
The output signal is fed back to the inverting input terminal through a resistor.
Positive feedback
The output signal is fed back to the inverting input terminal through a resistor.
Types
Inverting amplifier
Inverts the input signal. Input signal is fed to inverting input through
Here:
- Closed-loop voltage gain
Non-inverting amplifier
Input signal is fed to non-inverting input terminal. Inverting input terminal is
grounded through
Here:
- Closed-loop voltage gain
Summing amplifier
An extension of the inverting amplifier. Multiple input signals are added together.
Differential amplifier
Used to amplify the difference between two input signals.
Integrator
Input is fed to non-inverting input terminal through a resistor
Differentiator
Input is fed to inverting input terminal through a capacitor