Detector SNR & Comparison Calculator

Calculate signal-to-noise ratio, NEP, and minimum detectable power for photodiodes, APDs, and PMTs. Compare two detector configurations side by side.

Photodetector SNR is set by the interplay of three noise sources: shot noise from photocurrent and dark current (∝ √I), Johnson (thermal) noise from the load resistor (∝ √(4k_BT/R_L)), and — for APDs and PMTs — excess multiplication noise characterized by the McIntyre factor F(M). This tool computes signal current, all three noise components, total noise, SNR in dB, noise-equivalent power (NEP), and minimum detectable power for three detector types: photodiode (no internal gain), APD (gain M, ionization ratio k), and PMT (dynode chain gain, stage count). A Compare Two mode places two detector configurations side by side for direct SNR and NEP comparison. Inputs include wavelength, optical power, quantum efficiency, dark current, load resistance, bandwidth, and temperature.

Detector Parameters
Signal
Responsivity
0.4084A/W
Signal current
408.4nA
Noise
Shot noise
36.173pA
Dark noise
1.790pA
Johnson noise
127.7pA
Total noise
132.7pA
Dominant source
Johnson noise
Performance
SNR
3077.7
SNR
69.764dB
NEP
3.249pW/√Hz
Min detectable power
324.9pW
Abridged Optics — v1.0Uses exact physical constants (h, c, e, k_B). APD excess noise uses the McIntyre model. PMT excess noise uses F ≈ 1 + 1/δ where δ = M^(1/n).

All information, equations, and calculations have been compiled and verified to the best of our ability. For mission-critical applications, we recommend independent verification of all values. If you find an error, please let us know.