Tektronix 071-0590-00 user manual Other Bert Features, Eye Width Measurement, Auto-Synch

BERT Primer

Other BERT Features

In addition to measuring Bit Error Rate, BERTs may have additional features which enhance ease of use or expand test capabilities. Some of these might be:

*Eye Width Measurement

*Auto Synch Feature

*Pattern Locking Methods

*Pattern Loading Software

*Error Insertion

*Internal Jitter Generation

Eye Width Measurement

Since the BERT Receiver must have the ability to delay the received clock, it may have the ability to run the clock edge through a range sufficient to cover the received data “eye” . The “eye” width is the time during which the received data exhibits clean logic “1” or “0” levels. Ideally the “eye width” is one over the bit rate. At the edge of the “eye”, the signal is transitioning from one level to the other. The “Eye Width” for any Error Rate is a measure of a system’s timing and jitter tolerance. A designer might have to meet a spec such as “eye width at 500Mb/s and 10-9BER must be 1.0ns or greater”. The manufacturer is then confident that there is sufficient margin in his product to live up to his customers’ expectations. Vertical compression of the eye (from ISI, echoes, regenerator output variations, decision-level instability, etc.) from ideal can be used to extrapolate error rate, and derive minimum S/N ratios to assure specified performance.

The user should run the test equipment back-to-back (i.e., Transmitter connected directly to Receiver with no device in the test path) first, to establish maximum eye width. BERTs inherently have their own set-up and hold times, so back-to- back results will always be a little less than perfect.

Auto-Synch

Auto-Synch is the ability of the BERT Receiver to search in time and in amplitude level for the optimum place to put the Clock edge for the cleanest logic level information. This positioning must be done, whether automatically or manually, before any meaningful BER measurement can be made. All of our BERT products have this Auto-Synch feature.

B-10 GB1400 User Manual