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Beginner
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Impedance Matching for differential tracks

The Max 10's LVDS IO user guide mentions matching trace impedance with that of termination resistor. However in the figure given below they have mentioned single ended trace impedance of each of the differential traces to be 50Ω and terminating resistor's value as 100Ω.

Differential Impedance.PNG

 

Now how can the differential impedance of traces be matched with that of termination resistor given that differential impedance is defined as

Differential Impedance vs Single Ended Impedance.PNG

 

where,

Zd = differential impedance

Zo = single ended impedance

d = trace separation

h = dielectric thickness

 

I have tried to evaluate from the above equation using some standard values of h but didn't end up with 100Ω differential and 50Ω single ended impedance.

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Valued Contributor II
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The termination scheme used in LVDS lines forMAX10 follows a 3-resistor or single-resistor external termination scheme. You can refer to the following LVDS termination guide lines for more information.

 

https://www.intel.com/content/www/us/en/programmable/documentation/sam1394433606063.html#sam13944362...

 

So, when you use the scheme mentioned above you will have to keep the line impedance at 50ohm and 100ohm and then calculate the values of Rs/Rp depending on the type of scheme used.

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Employee
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Hi ,

Also try to use the IBIS simulation .

 

Regards,

RS

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Beginner
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Thanks for replying.

 

@Abe​ 

The three resistor termination scheme needs to be employed only in case of emulated transmitter. I am more interested in the termination for a receiver and the impedance of the LVDS lines, both single ended and differential.

 

@RahulS_Intel​ 

Sure. Will try. Any tool you recommend? Have tried Hyperlynx before but because of unavailability of IBIS models for some components other than MAX10, had to drop that idea.

 

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Employee
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@SMS​ 

Let me know Max 10 part no: that you are using does not have IBIS model.

 

Regards,

Rahul S

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Beginner
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@RahulS_Intel​ 

I meant components other than Max 10 in my circuit. I am generating the IBIS model for the specific Max 10 that I am using. Thanks

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