LeCroy DDA 7 Zi series, Operator'S Manual

Page: 503 / 544

Operator's Manual
WP700Zi-OM-E-RevA
502
can be specified.
possible error
messages:
"Must set #states before STATE info!" - see note 4 above.
"State <number>?? Expected states 0 to <STATES - 1>!"
"State <number>: must be -1 < expected level < 1!"
keyword:
STATES
arguments: <number from 4 to 16>
required?:
yes
Note:
STATES must appear before a STATE is specified
possible error messages: "#states must be >= 4 and <= 16!"
keyword: STEERING_LATENCY
arguments: <value 0 to 10>
required?:
no
Notes:
The DDA's channel emulation uses decision directed steering. This means that the PLL and
AGC are not determined based on the nearest level to each sample. Instead, we wait
STEERING_LATENCY samples and then steer based on what the sample should have
been according to the Viterbi detector. The DDA uses 6 for PR4, EPR4, and E2PR4. After 6
samples it is far more likely that the detector has already picked the correct path, and we
will steer toward the correct target. If this keyword is not seen, its value remains unchanged.
If it has never been set since power on, the default is 6. CAUTION: Increasing the steering
latency increases the delay for the steering control loops and may make them unstable. For
a 16 state signal (such as E2PR4), the detector uses the sample at STEERING_LATENCY
into the trellis, and four more preceding it (that is, further into the trellis) to determine the
expected value for the sample at STEERING_LATENCY. The difference between the actual
sample value and the expected value determines steering.
possible error
messages:
"STEERING_LATENCY must be >= 0 and <=10"
keyword: TOP_LEVEL_AS_FRACTION_OF_PEAK
arguments: <number, 0.5 to 1.5>
required?:
yes
Notes:
This is the ratio of the nominal "1" sample level to the peak height of the VCO sync pattern.
This is used in our emulated channel's acquisition of the proper sampling phase and levels.
For example, using a 2T sync pattern, PR4 has 1, +1, -1, -1 & and the peaks are
significantly higher. For PR4, the DDA uses 0.7854 for this value. For EPR4, a 2T pattern is
0, +1, 0, -1& so the peaks are +1 and -1. For EPR4 the DDA uses 1.0000 for this value. For
E2PR4 a 2T pattern is +0.6667, +0.6667, -0.6667, -0.6667, and the peaks are higher,