[SI-LIST] Max operating frequency of LVDS driver
- From: Raymond.Leung@xxxxxxxxxxx
- To: si-list@xxxxxxxxxxxxx
- Date: Mon, 10 Feb 2003 09:23:41 +1000
HI Sunil,
My answer to the first question would be yes in principle, if the eye diagram
quality is not a problem. In this way, I have puzzles on your next
question since the equation of tr=0.3tui has already stated that the theoretical
max. frequency when tr is really worst is independent of voltage level.
In this sawtooth waveform, the tr is the same for whatever max. swing.
However, in reality of chip driving capability, worst tr would usually be
together
with worst voltage swing. In this case the min. swing would be a good
guess if you want to test your receiver and/or your board.
Regards,
Raymond
---------------------- Forwarded by Raymond Leung/sdc on 10/02/2003 09:06
---------------------------
sunil-chandra.kasanyal@xxxxxx on 08/02/2003 00:03:11
Please respond to sunil-chandra.kasanyal@xxxxxx
To: si-list@xxxxxxxxxxxxx
cc: (bcc: Raymond Leung/sdc)
Subject: [SI-LIST] Max operating frequency of LVDS driver
Hello all,
My question is regarding to TIA/EIA-644-A standard on LVDS.In this
standard it is specified that the maximum transistion time for the output
signal is 0.3tui. Where tui is the unit interval of output waveform. If I
know the 20% to 80% rise time of the output wave of LVDS driver I can
calculate its maximum frequency of operation (f=0.3/2*tr), by applying
the condition tr=0.3tui.Is this approach for calculating maximum
operating frequency is justified?
If yes, my second question follows:
Rise time tr specified here is the 20% to 80% of Vss, where Vss=2*Vt. Vt
is the output differential swing. This Vt may be anything from 250mV to
450mV. Suppose in my case this Vt comes 300mV, then Vss will be
2*300=600mV. But the minimum Vss for LVDS driver is 2*250=500mV. Now for
calculating maximum operating frequency, should I take tr equal to 20% to
80% of the total Vss swing of 600mV or should I consider only 500mV swing
of Vss, means tr equal to 20% to 80% of the 500mV portion of Vss.
If I say that I should take only 500mV portion into consideration,
because I am going to calculate maximum operating frequency, am I wrong?
Why?
Thanks in advance,
Thanks and Regards,
Sunil C Kasanyal
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