Physics and Engineering of Radiation Detection

8.9. Electronics Noise 515

whereAis a system dependent constant of proportionality. The above expression
when multiplied by the system bandwidth fgives the total noise voltage, that is

vf=

√

A

fα

f. (8.9.17)

Unfortunately even though 1/fnoise is exhibited by most natural systems, its
sources are not fully understood. The electronic components based on MOS tech-
nology are most affected by this noise. On the other hand, it is negligibly small
for usual metallic conductors. Experimental determination of 1/fnoise in detection
systems is of prime importance specially for the ones that are supposed to work at
high resolution. This involves determining the total noise power density at different
frequencies using a spectrum analyzer. The spectrum analyzer is needed to perform
the Fourier transformation of the signal and averaging the noise power density. A
typical result of such an experiment is shown in Fig.8.9.2.

log(Noise Power Density)

log(Frequency)

Figure 8.9.2: Typical 1/fnoise spec-

trum.

The good thing about 1/fnoise in electronic systems is that it can be decreased
by improving the design and quality of the electronic components constituting the
system. Of course another approach is to work at higher frequencies, if other factors
allow.

A.4 QuantizationNoise.......................

If the process of analog to digital conversion involves step-wise or discrete sampling
of the analog signal, the variation in signal at each step has sharp edges. This
introduces high frequency noise in the system. The usual method to eliminate this
noise is to block the high frequencies by using a low pass filter.