VTI Instruments Corp.
APPENDIX B
72
The digital low-pass filter is not effective at f
CLK
± 0.58*f
DATA
so additional analog low-pass filtering
is provided to eliminate signals with frequencies in these bands. The corner frequency of the analog
anti-aliasing low-pass filter is fixed regardless of the selected data rate. The table below shows the
critical frequencies for each data rate at which aliasing can occur and at which the analog low-pass
filter needs to provide attenuation.
Model
Oversampling Ratio ( f
CLK
/ f
DATA
)
Oversampling
Clock (f
CLK
)
32
64
128
256
Data Rate (f
DATA
) - Samples per Second (Sa/s)
EMX-4250
EMX-4251
4,118,282
4,156,293
4,175,299
4,194,304 Hz
6,434,816
6,494,208
6,523,904
6,553,600 Hz
EMX-4350
EMX-4380
12,869,632
12,988,416
13,047,808
13,077,504
13,107,200 Hz
16,473,129
16,625,172
16,701,194
16,739,205
16,777,216 Hz
19,637,500
19,818,750
19,909,375
19,954,688
20,000,000 Hz
Table 4-9: Critical Frequencies for f
DATA
EMX-4350/4380 Anti-Aliasing
Figure 4-25: EMX-4350/4380 ADC Digital Filter Frequency Response
