Calculator KB-41
Operational amplifier calculator
Only two resistors set the gain, and the chip itself has almost no effect on it.
Result
In brief: Calculate an operational amplifier in inverting and non-inverting configurations: gain, output voltage, GBW bandwidth, and saturation check. Example: Gain: 11 ×.
Calculation example
| Circuit | Non-inverting |
|---|---|
| Rf | 100000 Ω |
| Rg | 10000 Ω |
| Input signal | 0.2 V |
| Output limit | 12 ±В |
| Gain-bandwidth product (GBW) | 1 MHz |
| Gain | 11 × |
|---|---|
| In decibels | 20.8 dB |
| Output | 2.2 V |
| Bandwidth | 90.91 kHz |
| Input impedance | very large |
How it is calculated
Inverting: K = −Rf / Rg
BW = GBW / (1 + Rf / Rg)
An op-amp keeps its inputs at nearly the same voltage, while feedback determines how it does so. The higher the gain, the narrower the bandwidth: their product is constant.
What to look for
- Most op-amps cannot swing all the way to the supply rails. Not all are rail-to-rail: check the datasheet.
- For small signals and high gain, input offset voltage and noise matter: the LM358 isn't suitable for every application.
Frequently asked questions
How do you calculate an op-amp's gain?
Non-inverting configuration: K = 1 + Rf / Rg; inverting configuration: K = −Rf / Rg. With 100 kΩ and 10 kΩ, the gains are 11 and −10.
What will the amplifier's bandwidth be?
BW = GBW / (1 + Rf / Rg). An LM358 with a GBW of 1 MHz and a gain of 11 will have a bandwidth of about 91 kHz.
Why can't an LM358 output the full supply voltage?
Its output falls about 1.5 V short of the positive supply rail. For full output swing, use rail-to-rail op-amps.
