ADLINK PCI-9524 - Manual (Page 73)

Operation Theory 57
ADLINK Technology Inc. PCI-9524
Copyright 2008 User’s Manual
sampling rate. Also note that the output data rate is 29.5 SPS
rather than 60 SPS, due to auto-zeroing. As the sampling rate
changes, the notches' frequency change accordingly.
Figure 4-4: The Effect of Auto-zero on Thermal Noise and
1/f Noise, ADC running at 60 SPS
Effect of Auto-zero on Thermal noise and 1/f Noise
-120
-100
-80
-60
-40
-20
0
0.00 10.00 20.00 30.00 40.00 50.00 60.00
Frequency (Hz)
A
tt
e
nu
at
io
n (
d
B
)
As many bipolar-input low-noise amplifiers, those used in PCI-
9524 start to assert their 1/f noise below 10 Hz, the gradually
increasing noise attenuation from below 20 Hz is a nice feature.
This also implies that a too-low sampling rate will not improve the
stability performance significantly, since noise attenuation may
start at a frequency much lower than where the amplifier's 1/f
noise emerges.
To successfully resolve low-level signals, always enable the auto-
zero and remote-sense function, keeping transducers and installa-
tion of PCI-9524 away from heat radiating sources, EMI radiating
sources, and free of mechanical vibration. Also, shield transducers
from airflow, and make sure all the connecting junctions are fas-
tened tight and free of oxidation.