Amplifier Gain (dB) Calculator

Amplifier gain in decibels: 20 · log₁₀(V_out/V_in)

To express amplifier gain in decibels (dB), you use GdB = 20 · log10(Vout / Vin) for voltage and GdB = 10 · log10(Pout / Pin) for power. Some handy reference points: +20 dB = 10× voltage, +40 dB = 100×, +60 dB = 1000×. Attenuation comes out as a negative dB. When you cascade stages, you just add the dB values together, and that's the main thing that makes the unit so handy. As an example, with V_in = 0.1 V and V_out = 10 V you get G_dB = 20 · log₁₀(100) = 40 dB. Add negative feedback and the closed-loop gain turns into Gcl = G / (1 + β · G). You lose some gain, but you gain linearity and bandwidth in return. A typical op-amp sits near 10⁵ open-loop gain (≈100 dB), which feedback then trims down to whatever closed-loop value you need.

Applications: audio, telecom, instrumentation, RF

You'll run into dB gain in audio amplifiers (classes A, AB, D), in telecom link budgets, in instrumentation amplifiers (the INA-series, used with strain gauges and thermocouples), across RF chains (LNA, mixer, PA), and in the sensor signal conditioning that sits ahead of ADCs.

FAQ

Why 20 for voltage and 10 for power? Power goes up with the square of voltage, and that factor of 2 from the squaring ends up folded into the multiplier sitting in front of the log.

Can dB be negative? It can. A negative dB just means attenuation, where the output is smaller than the input. You see it all the time with cables, filters and pads.

Why use negative feedback if it reduces gain? Because you're trading gain you have to spare for things you actually want: better linearity, a more predictable response, wider bandwidth and less distortion.

What is dBm? It's dB referenced to 1 mW into a defined impedance, usually 50 Ω in RF work, and it lets you state absolute power levels rather than just ratios.