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226 Chapter 7
Digital Signal Interface Module
Clock Timing
Clock Timing for Parallel Interleaved Data
The N5102A module provides the capability to interleave the digital I and Q samples. There are two choices
for interleaving:
•
IQ, where the I sample is transmitted first
•
QI, where the Q sample is transmitted first
When parallel interleaved is selected, all samples are transmitted on the I data lines. This effectively
transmits the same number of samples during a sample period on half the number of data lines as compared
to non-interleaved samples. (A sample period consists of an I and Q sample.) Clocks per sample is still a
valid parameter for parallel interleaved transmissions and creates a reduction in the sample rate relative to
the clock rate. The clocks per sample selection is the ratio of the reduction.
Figure 7-5 shows each of the
clocks per sample selections, for a parallel IQ interleaved port configuration, using a word sized of four bits
and the clock timing relative to the I and Q samples. For a parallel QI interleaved port configuration, just
reverse the I and Q sample positions. For input mode, the clocks per sample setting is always one.
Figure 7-5 Clock Timing for a Parallel IQ Interleaved Port Configuration
Q sample
4 bits per word
I sample
4 bits per word
1 Sample Period
1 Clock Per Sample
1 Clock
The I sample is transmitted on one clock transition and the Q sample is transmitted on the
Clock
other transition; the sample and clock rates are the same.