Equivalent circuit of non-ideal Op Amp.
\(\displaystyle v_{d} = v_{2} - v_{1}\)
\(\boxed{v_{o} = Av_{d} = A(v_{2} - v_{1})}\)
where:
- \(A\) is called the open-loop voltage gain because it is the gain of the op amp without any external feedback from output to input.
- \(V_{d}\) is the differential input voltage.
- \(R_{i}\) is the input resistance.
- \(R_{o}\) is the output resistance.
The op amp senses the difference between the two inputs, multiplies it by the gain \(A\), and causes the resulting voltage to appear at the output \(v_{o}\).
| Parameter | Typical range | Ideal values |
|---|---|---|
| Open-loop gain, \(A\) | \(10^{5}\) to \(10^{8}\) | \(\infty\) |
| Input resistance, \(R_{i}\) | \(10^{5}\) to \(10^{13}\,\Omega\) | \(\infty\,\Omega\) |
| Output resistance, \(R_{o}\) | \(10\) to \(100\,\Omega\) | \(0\,\Omega\) |
| Supply voltage, \(V_{CC}\) | \(5\) to \(24\,V\) |