Specifications

B-2

Appendix B

Setting Error Detector Sync Thresholds

Introduction

The following paragraphs provide information on how to select the correct sync threshold

for the current pattern. Failure to set the correct sync threshold may result in incorrect

synchronization, which may cause errors or clock-to-data alignment failure. Sync

threshold is setup using the hardkey, then selecting a threshold from the

available range of softkeys.

Setting Sync Thresholds

To obtain accurate results you must choose a sync threshold which results in optimum

alignment for the current pattern.

For any pattern other than a PRBS pattern, the error rate caused by non-alignment with the

incoming data is dependent on the data pattern. Here the sync threshold should be chosen

so that only EXACT pattern alignment results in the error detector gaining sync. For

example, consider a pattern of 1000 ones and 1000 zeros as shown in the following figure.

With reference alignment 1 the patterns are totally out of phase and the error rate is

100%, but as the reference moves closer to optimum alignment the error rate drops

gradually to zero. For exact alignment, the sync threshold must be set lower than the error

rate caused by a 1 bit misalignment, in this case 1E03.

Figure B-1 Error rates due to pattern misalignment

In the general case, for an n bit pattern length the sync threshold should be set lower than

2/n if optimum alignment is to be achieved.

Clock-to-Data Alignment Failure

If you are experiencing a failure or intermittent failure when you perform clock-to-data

alignment on a User Pattern, try setting the eye edge threshold to a new value, and retry

sync & audio