Re: Si570 LVDS Output Impedance

Clifford Heath
 

The Si570 data sheet says: "Available LVPECL, CMOS, LVDS, and CML outputs".
So the correct output coupling depends on which one you use.

LVPECL (fastest) requires 50 ohms termination to Vdd-2.0V.
LVDS and CML require 100 ohm differential (not supply-referenced).
CMOS swings within about 0.4V of the rails.

Clifford Heath.

On 22 Apr 2019, at 12:39 pm, Clifford Heath via Groups.Io <clifford.heath=gmail.com@groups.io> wrote:

Check that you get the right impedance ratio - remember that it is the
square of the turns ratio.

I haven't checked the data sheet to see if the Si570 output is DC (ground)
referenced. If not, I would decouple the CT to ground with a capacitor
anyway. But check the data sheet.

Clifford Heath

On Mon, 22 Apr 2019, 02:29 Alfredo Mendiola Loyola via Groups.Io
<mendiola_loyola=yahoo.com@groups.io> wrote:

Hello,

If I connect a Center Tap of an 1:4 Transformer (Secondary) to the LVDS
outputs I will get a 50 Ohm output impedance on the Primary?

Schematic:

https://docs.google.com/viewer?a=v&pid=sites&srcid=ZGVmYXVsdGRvbWFpbnxhZTVwaHJhZGlvbm90ZWJvb2t8Z3g6NjA1OGNmZjAxNjQ5ZDhmNQ

I understand that the output impedance of each output of the si570 is 100
Ohm (LVDS), When I connect each output of the si570 to the transformer
Secondary I will get 200 ohm and 50 ohm on the Primary (200 4 = 50 ohm).

Do I have to connect the center tap of the secondary to ground?

Transformer Datasheet:
https://www.coilcraft.com/pdfs/pwb.pdf
Model: PWB-4-BL

73
Alfredo Mendiola
OA4AJP



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