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Application Note - Auto Search Synchronization
GB1400 User Manual 2-43
3. If unsuccessful, it will then try the following data delays in the previous step-
1/4 per, 3/4 per, 1/8 per, 5/8 per, 3/8 per, 7/8 per.
4. If sync is still not found, go back to the first section Find Data V-Threshold.
Auto Search will determine the Data Delay.
1. Initially the entire delay range (0nS to 3.99 nS) in steps of 70pS will be
sampled for 20mS each for error rate. The selectable BER Threshold will be
used to determine if the delay settings are within the data eye crossings.
2. The largest contiguous block of delay measurements with error rates below
the threshold will be found. Using that data, the transitions from data
crossing to data eye can be found.
NOTE: This will be with 70 pS granularity.
If two transitions are within the receiver delay range, two points will be re-
examined such that the data eye center and width can be determined. (See
illustration /diagram #1, Case #1).
If BOTH ends of the clear block are the edges of the receiver delay range (no
Crossing found), set the delay to the middle of the receiver delay range.
STOP. No eye width is available.
If NO clear block is found (no crossing found), set the delay to the middle of
the receiver delay range.
STOP. No eye width is available.
If ONE end of the clear block is on the edge and the width of the clear block
is less than half the clock period, set the delay to that edge.
STOP. No eye width is available.
If ONE end of the clear block is on the edge and the width of the clear block
is greater than half the clock period, two transition points, A and B, will be
re-examined further (see Diagram 1, Cases 2 and 3).
3. If the transition points are to be evaluated further, an area 70pS wide will be
examined in steps of 5pS for 20ms each. This starts from the first delay
setting in the data crossing and goes to the first delay setting in the data eye
(see Diagram 2).
4. After the areas have been measured for error rate, the areas will be examined
for the first transition from below the threshold to above the threshold staring
with the end closest to the data eye center. These points will be the NEW
transition points.
5. Each of these NEW transition points will be re-examined for a length of time
based upon the SAMPLE size. The error rate will be compared with the
selectable BER Threshold.
If the error rate is below the Threshold, the next point away from the Data
Eye Center will be examined, and so on, until the error rate transitions to
above the Threshold. The last point below the Threshold will be the TRUE
transition point.