FPGA Central

I only know eye diagram can use to analyse code disturbing.But I
don't know what the other generally use of it and how to analyse
it.Could you help me?
Best regards!

On 30 Sep 2004 20:54:40 -0700, "Bruce Sam" <[email protected]>
wrote:

>I only know eye diagram can use to analyse code disturbing.But I
>don't know what the other generally use of it and how to analyse
>it.Could you help me?

For relatively simple modulation formats, an eye diagram provides an
easy way of *roughly* measuring the margin in a communications system.

Here's an example:
http://fractional-divider.tripod.com/eye.pdf

The width of the eye provides information about tolerance to jitter,
and the height of the eye gives information about tolerance to
additive noise.
Eye closure (inadequate width or height) is probably due to ISI, so
the eye diagram also gives you an idea of the performance of your
equaliser.


Many communication systems (particularly those that are standardised)
have 'pulse masks' which are used for compliance testing. The eye
must fall within the mask.

See (for example) any of the masks in ITU-T G.703
http://www.itu.int/rec/recommendatio...nt=T-REC-G.703

Many modern oscilloscopes have pulse masks for all the popular
communications standards built in. Just press the right button, and
the 'scope will draw the mask on the screen and count the number of
samples that fall outside the mask. This can be used to get a crude
estimate of BER. However this sort of testing is usually done on the
transmitter output, where any mask violation is regarded as design
fault.
(In my day, we had to stick bits on tape on the 'scope screen.)

Regards,
Allan