LVDS without termination

Kolja Sulimma · 2005-01-28T10:11:47+00:00

Austin Lesea wrote at 2003-10-02 08:03:57 PST"Also look at what happens when you do not have a 100 ohm termination. For some signals, and lengths of pcb, it may not be required." and"If I may suggest, use LVDCI_25_DCI only for clock inputs, or a fewsignals."I need to get 16 LVDS pairs into one edge of a Spartan-3. This is really simple to layout without termination resistors and really complicated (with our board technology) if I add termination resistors.Without termination the maximum signal length is 4mm. The chip driving the LVDS signals uses current mode output drivers.My question now is what will happen if I try to use LVDS without termination? Will the current mode drivers produce a very large output signal swing? dangerous overshoot? (They are 3.3V powered)We want to run data at 480 Mbps over each pair so surely reflections with less than 30ps roundtrip time are not that much of a problem?If the current mode drivers require the 100R at their output, could I add them at the source? To get many resistors much closer than 4mm on a bga is difficult anyway.Thank you in advance for your suggestions.Kolja Sulimma

Jan 28, 2005 21 Replies

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Uwe Bonnes 21 years ago

Have a look at digikey. They have a lot of special footprints, e.g. RT1710B6P.

Hope this helps

Uwe Bonnes bon@elektron.ikp.physik.tu-darmstadt.de Institut fuer Kernphysik Schlossgartenstrasse 9 64289 Darmstadt --------- Tel. 06151 162516 -------- Fax. 06151 164321 ----------

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Gabor 21 years ago

are

0.5

route

Look at the data sheet. The connection looks like:

1 --------------- 8 | R E S | 2 --------------- 7

and so on, where all RES are 100 ohms. It is really made for this type of termination. The only thing you would like is finer pitch.

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