Noise Figure Calculator

Noise figure (NF) measures the degradation of the signal-to-noise ratio caused by components in a signal chain. Mathematically, it is defined in decibels (dB) as the difference between the input SNR in decibels ($ISNR_{dB}$) and the output SNR in decibels ($OSNR_{dB}$), expressed through the fundamental equation: $NoiseFigure_{dB} = ISNR_{dB} - OSNR_{dB}$. Alternatively, noise factor ($F$) can be expressed linearly using the ratio $F = 10^{(NoiseFigure/10)}$. For multi-stage amplifiers, Friis' formula is used to calculate the cumulative noise factor and total gain across cascaded components, helping engineers predict how early-stage amplification heavily dictates total system noise.

Imagine you are testing an RF receiver module in a communication system. Your input signal-to-noise ratio measured at the preamplifier input is 40 dB ($ISNR_{dB} = 40$), and the resulting output signal-to-noise ratio after processing is 35 dB ($OSNR_{dB} = 35$). To find the noise figure, you subtract the output SNR from the input SNR: $40\text{ dB} - 35\text{ dB} = 5\text{ dB}$. This means the internal components of your amplifier introduced enough thermal and electronic noise to degrade the signal quality by 5 dB.

When designing cascaded amplifier chains, always prioritize placing your lowest-noise, highest-gain amplifier (LNA) as the very first stage in the circuit. According to Friis' formula, the noise contribution of subsequent stages is divided by the cumulative gain of all preceding stages, minimizing their impact on the overall system noise figure. Always ensure your input and output impedance matching is correct, as reflections can introduce measurement errors in your SNR readings.