Start from the governing relation
\[v_o=A_{OL}(v_+-v_-)\]
This is the smallest equation that preserves the physics needed for the formula.
Choose the model state or domain.
FORMULA / 005
Ideal op-amp golden rules
Interactive derivation module for Ideal op-amp golden rules.
\[A_v=-\frac{R_f}{R_{in}},\quad A_v=1+\frac{R_f}{R_g}\]
Connects the formula to engineering interpretation, limits, and computation.
Problem Definition
Problem statement and variable definition
A breadboard amplifier may match the gain equation at low frequency but lose gain near the op-amp GBW limit.
Core variable legend
| Symbol | Quantity | Unit | Meaning |
|---|---|---|---|
| $A_{OL}$ | Open-loop gain | V/V | Large gain that enables virtual short. |
| $R_f$ | Feedback resistor | ohm | Sets closed-loop gain. |
| $GBW$ | Gain-bandwidth product | Hz | Speed limit of the op-amp. |
Analytical Derivation
Model assumptions and analytical derivation
Model simplifications
| Item | Assumption |
|---|---|
| Assumption 1 | Linear time-invariant or locally linear behavior is assumed when using transfer functions. |
| Assumption 2 | Parameters are treated as constant over the analysis interval. |
| Assumption 3 | Numerical plots are educational approximations, not full circuit or field solvers. |
Apply engineering assumptions
\[v_o=A_{OL}(v_+-v_-)\]
The model is simplified so the dominant mechanism is visible.
Drop second-order parasitics unless they are the topic.
Rearrange to the working formula
\[A_v\approx-\frac{R_f}{R_{in}}\]
The final form is the one used for design, simulation, or measurement review.
Algebraic rearrangement.
parameter $\to0$dominant term remainsThe formula reduces to its simplest physical behavior.
parameter $\to\infty$parasitics and implementation limits dominateThe closed-form equation becomes a warning rather than a full implementation model.
Parametric Verification
Parametric simulation and numerical verification
Use the sliders to change the physical parameters and watch the formula expose its behavior. The metric panel keeps sample count and compute latency visible so the visualization remains an engineering instrument, not only a picture.
INTERACTIVE MODULE
Closed-loop bandwidth from GBW
Engineering Application
Engineering application and implementation notes
Design rules
- Check units before trusting numeric output.
- Sweep the key parameter through the critical region, not only the nominal value.
- Validate the simplified formula against measurement or simulation before committing hardware.
Core algorithm
python
import numpy as np
def inverting_gain(rf, rin):
return -rf / rin