Chapter 2
Theory of Operation
©
National Instruments Corporation
2-17
Figure 2-14.
Multirate Scanning without Ghost
In Example 3, channel 0 is sampled correctly. Although channel 1 is
sampled twice, it does not yield a 50% duty cycle. This type of acquisition
will result in imprecise rates. Figure 2-15 shows the relative occurrences of
convert pulses in Figure 2-14.
Figure 2-15.
Occurrences of Conversion on Channel 1 in Example 3
To rectify the problem, use ghost as illustrated in Figure 2-16.
Figure 2-16.
Successive Scans Using Ghost
The shaded conversions are ghost conversions. The short arrows indicate
channel 0 samples and the long arrows indicate channel 1 samples that are
actually stored in the FIFOs.
0
0
0
1
1
Sampling Rates
Channel 0: Channel 1 = 3:2
Start
Convert
t
t
Channel 1, Example 3
Convert
t
2t
t
0 1
0 1
0 1
0 1
0 1
0 1
Start
Convert
