Signal-to-Noise Optimization. Noise Sources Most Commonly Encountered 1. Detector Noise 2. Shot Noise 3. Flicker Noise. Detector Noise. Associated only with the detector, and therefore constant for a given set of detector conditions. N detector = Constant (S/N) det S. Shot Noise.
Noise Sources Most Commonly Encountered
1. Detector Noise
2. Shot Noise
3. Flicker Noise
Associated only with the detector, and therefore constant for a given set of detector conditions.
Ndetector = Constant
Noise associated with the random transfer of electrons across a p-n junction.
Ex: Whether or not a single photon falling on a detector will actually produce a signal.
S = measured signal
e = charge on electron
Δf = frequency bandwidth
Shot noise is usually the limiting source of noise near the detection limit
Random noise with a 1/f frequency dependence.
f = sampling frequency
Flicker noise includes slow drifts in signal intensity caused by such parameters as temperature, flow rates, etc.
where ξ = flicker factor (unit-less)
(S/N)fl = S/ξS = 1/ξ
ξ 1/f so (S/N)fl f
and f = frequency of data collection
(S/N)fl = 1/ξ
determine the slope (m)
1. m = 1 → Detector Noise
2. m = ½ → Shot Noise
3. m = 0 → Flicker Noise
When we measure N experimentally, it is often a combination of all of the noises present in the system. The preceding equations are useful to determine which type of noise dominates in a certain situation.