Calculator
Example Data Table
| Vout (V) | V+ (V) | V− (V) | Vd = V+ − V− (V) | Open Loop Gain | Gain (dB) |
|---|---|---|---|---|---|
| 5.0000 | 0.0025 | 0.0000 | 0.0025 | 2000.0000 | 66.0206 |
| 8.2000 | 0.0040 | 0.0005 | 0.0035 | 2342.8571 | 67.3945 |
| -6.5000 | 0.0010 | 0.0040 | -0.0030 | 2166.6667 | 66.7177 |
Formula Used
Differential input voltage: Vd = V+ − V−
Open loop gain: AOL = Vout / Vd
Gain in decibels: Gain(dB) = 20 × log10(|AOL|)
Differential input in microvolts: Vd(µV) = Vd × 1,000,000
This calculator uses measured voltage values to estimate amplifier open loop gain and to check whether the chosen output is close to the entered supply rails.
How to Use This Calculator
- Enter the measured output voltage.
- Enter the non-inverting input voltage.
- Enter the inverting input voltage.
- Optionally enter positive and negative rail values.
- Press the calculate button to get linear gain, decibel gain, rail margins, and the graph.
Engineering Notes
Open loop gain is a core amplifier parameter used in analog design, testing, and troubleshooting. Small input differences can create large output changes, so accurate measurements matter. The decibel view helps compare very high values quickly, while the rail margin check highlights possible saturation during real measurements.
FAQs
1. What is open loop gain?
Open loop gain is the amplifier gain without external feedback. It compares output voltage to the differential input voltage. Very high values mean tiny input differences can create large output changes.
2. Why calculate gain in decibels?
Decibels make very large gains easier to compare and review. They are also useful when reading datasheets, checking frequency response, and comparing amplifier behavior across different designs.
3. Why can the linear gain be extremely large?
The differential input is often only microvolts or millivolts. Dividing a normal output voltage by a very small input difference naturally produces a very large open loop gain.
4. What happens if V+ equals V−?
The calculation becomes undefined because the differential input is zero. Enter measured values that show a real difference between the two inputs before calculating gain.
5. Do supply rails change open loop gain?
Supply rails do not directly define open loop gain, but they do limit output swing. If the output is near a rail, saturation can distort the measurement and reduce confidence.
6. Can the calculator return a negative gain?
Yes. A negative result means the entered output polarity opposes the differential input polarity. That may reflect measurement polarity, reference direction, or amplifier behavior in the supplied data.
7. Is open loop gain the same as closed loop gain?
No. Closed loop gain includes the effect of feedback networks. Open loop gain describes the amplifier core before external feedback shapes accuracy, bandwidth, and stability.
8. When is this calculator useful?
This calculator is useful during lab measurements, validation work, troubleshooting, and engineering checks. It helps compare observed voltage behavior with expected amplifier performance and operating limits.