DS90UB947-Q1: Two serializers connected to the same LVDS input?

Hello Mark,

can you clarify what do you mean by 2 SER to the same LVDS input data? Do you mean you want to split all oLDI signal lanes into two and feed into the Serializers? or you are planning to use a MUX to do the job?

And where this 100 ohm termination will be placed? Can you provide a block diagram?

Yes idea is to split each LVDS pair and feed to two serializers at the same time.  Would like to do this without a mux or buffer if possible. 

100 ohm would be placed at serializer farthest away from source.

Block Diagram

FPDLink Loop Back.pdf

Hi Hamzeh,

Thanks for pointing out the repeater details in the data sheet.  

Since part availability is a concern right now, the customer is asking if he can do the split on the FPD Link side of one DS90UB947 serializer? In this case, the serializer outputs would be split to connect to two independent deserailizers (UB948 and UB940N). The application requires a dual link configuration between the serializer and deserializer so Replicate mode is not applicable. 

I don't think this idea will work, but wanted to ask just in case I'm wrong. 

Hi Hamzeh,

I think you misunderstood my question. They would send the same data to both DES. They basically want to send the same data to two different Deserializers with the fewest amount of devices. 

1. The first idea was to split the data at the inputs of two serializers, each with a one-to-one connection to a deserializer.  This would take two serializers and two deserializers. This data connection on the SER input would be similar to Repeater mode. This was my original post.

2. The second idea is to use one serializer, and split its output to two different serializers.  Same data to both. Both need to have dual links to support the display resolution. (See attached block). 

FPDLink Loop Back 2.pdf

Mark,

I recommend the first option, i.e. to split the oLDI data as per datasheet repeater section.

The second option will degrade the quality of the FPD-Link signal and also you may have some Back channel communication issues.

Thanks Hamzeh,

Is there any way to turn off the back channel on a deserializer (DS90UB940 in this case)?  I can't find any way to do this in the data sheet. 

Also, going back to the Repeater Fan-out suggestion to support the first option - Do we have a reference design which implements the fan-out connections of section 7.3.14.2.1 in the data sheet?

Hi Hamzeh,

Thanks for the schematic.  I assume the termination resistors for the LVDS (oLDI) signals should be 100 ohms.  The schematic shows 100k ohms for these. 

Yes, this should be 100 ohms