VTI Instruments EMX-4016B, Руководство пользователя

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APPENDIX B 87
S
AMPLE
R
ATES AND
N
OMINAL
S
PANS
The sample rate is the data rate that user gets after decimation. While the Nyquist frequency is
<sample rate>/2, the usable frequency range after the decimation filter, without alias error, is the
nominal span. The nominal spans are calculated as <sample rate>/2.56. The frequency region above
the pass-band (Span) can be alias contaminated. It is called guard-band.
Model EMX-4350/4380 EMX-4250/4251
Clock Freq
409600 Hz* 524288 Hz* 625000 Hz* 131072 Hz** 204800Hz**
Top Span 160000*** 204800*** 244140.625*** 51200*** 80000***
1/5 32000 40960 48828.13 10240 16000
½- Stage1 80000 16000 102400 20480.00 122070.3 24414.06 25600 5120 40000 8000
Stage2
40000 8000 51200 10240.00 61035.16 12207.03 12800 2560 20000 4000
Stage3 20000 4000 25600 5120.00 30517.58 6103.52 6400 1280 10000 2000
Stage4 10000 2000 12800 2560.00 15258.79 3051.76 3200 640 5000 1000
Stage5 5000 1000 6400 1280.00 7629.40 1525.88 1600 320 2500 500
Stage6 2500 500 3200 640.00 3814.70 762.94 800 160 1250 250
Stage7 1250 250 1600 320.00 1907.34 381.47 400 80 625 125
Stage8 625 125 800 160.00 953.67 190.73 200 40 312.5 62.5
Stage9
312.5 62.5 400 80.00 476.83 95.37 100 20 156.25 31.25
Stage10 156.25 31.25 200.00 40.00 238.42 47.68 50.00 10.00 78.13 15.63
Stage11 78.13 15.63 100.00 20.00 119.21 23.84 25.00 5.00 39.06 7.81
Stage12 39.06 7.81 50.00 10.00 59.60 11.92 12.50 2.50 19.53 3.91
Stage13 19.53 3.91 25.00 5.00 29.80 5.96 6.25 1.25 9.77 1.95
Stage14 9.77 1.95 12.50 2.50 14.90 2.98 3.13 0.63 4.88 0.98
Stage15 4.88 0.98 6.25 1.25 7.45 1.49 1.56 0.31 2.44 0.49
Stage16
2.44 0.49 3.13 0.63 0.37 0.07 0.78 0.16 1.22 0.24
*EMX-4350/4380 clock frequencies can be divided by 2, 4, or 8 to obtain lower spans.
**EMX-4250 clock frequencies can be divided by 2 or 4 to obtain lower spans
***While the programming API defines nominal span = sample rate/2.56(0.39fs), the actual pass-band at the top span is
0.424 fs for 4350/4380, 0.4545fs for 4250/51.
Table A-1: Nominal Span (Sample Rate / 2.56)
G
ROUP
D
ELAYS
With EMX-4250/51, a filter in A/D converter introduces 39 samples group delay, and with for
EMX-4350/4380 it is 28 samples. This delay is about 45 µs at 625000 Hz.