Architecture of Multidrop LVDS

Hi Jeffrey,

Could you re-post your image? It appears the link is broken.

Regards,

Michael

Thanks Michael for the quick reply. I've just re-posted. Can you see it now?
Regards
Jeffrey

Hi Jeffrey,

Yes, I can see it now! We'll give this a look and get back to you with suggestions.

Michael

Jeffrey,

Unfortunately as you add receivers to this architecture, the maximum datarate which can be supported decreases.  For an interface of ~ 300 Mbps only a few (3-4) receivers could be attached to this type of interface.  With 200 receivers, the maximum datarate would be closer to 1 Mbps.

Regards,

Lee

Thank you Lee for quick answer.

The reason of speed decrease is because Many LV001 are in series?

In my case, do you have any solution for this multidrop LVDS?

Thanks and regards

Jeffrey

Jeffery,

All the DS90LV001 receiving devices are connected in parallel.  As receivers are added to this transmission line the signal will slow down and get distorted.  This combination will limit how fast the signals can transition and still be received correctly.

For 200 receivers at 300 Mbps I am not aware of a cheap solution.  Have you considered using 1Gb Ethernet?

Regards,

Lee

Understood,Thanks Lee
We thought about to put all receiver in series,means transmitter TX to receiver #1 RX, receiver #1 TX to receiver #2 RX.......
But the problem is that if one receiver is down,the rest receiver after will not get any data which is a big impact. To fix this, I am thinking about MLVDS. If we decrease the speed to be lower than 150Mbps, do you have a solution?

I didn't think about The Ethernet solution. Can you propose me the chip sets?
Thanks and regards
Jeffrey

If we put all LV001 in series, would be OK?

Can you please confirm if below structure would be OK or not?

Jeffrey,

A serial chain like this will also create signaling issues.  Each DS90LV001 will add to the random and deterministic jitter on the signal by a small amount.  As this jitter accumulates the signal will eventually become unusable and bit errors will result.

In order to eliminate the possibility of one receiver crashing the whole system I use use a 1Gb Ethernet network to transfer the data to all 200 receivers independently and route data back to the transmit device.   

Regards,

Lee

Thanks Lee,
In serial chain, the DS90LV001 is almost connected as point to point. I don't understand why it still cause problem. DS90LV001 is not used point to point? Or are you saying LVDS can't support such architecture.

"use a 1Gb Ethernet network to transfer the data to all 200 receivers independently and route data back to the transmit device"
You mean Transmitter should have 200 ports and each port only connect one receiver?

Regards
Jeffrey

Jeffrey,

At the speed you are trying to run, daisy chaining LVDS devices together over and over will eventually fail.  Depending on the implementation specifics it could be 2-3 links or 30 links.  LVDS and many other differential technologies are indeed optimized for point to point architecture.  Usually after a single point to point interface, the data is cleaned up and retimed by a clock-data recovery circuit (CDR).

Using Ethernet will provide your network some structure for hundreds of point to point links and the ability to retime the information between point to point links.  The common term used for Ethernet equipment used to tie all of your boards together is a "switch".  Since you have up to 200 nodes, you would likely need several smaller switches since 200 ports is very large for a single switch to handle.

Regards,

Lee 

Thanks Lee,

My last diagram is not really a daisy chain but a serial chain just it is not point to point but many points. I make the diagram in another way which could be clearer.

You explained already this kind of application will also add jitter/skew and lead to stability issue. It this is right?

I had a look at 1GB Ethernet chip sets. We can't afford the swicher with up to 200 ports. As 200 ports is only for one row. We could have up to 10 rows which means we need 2,000 ports. So we can't consider this direction.

I can give up daisy chain and design a serial chain with LVDS if possible.

Regards

Jeffrey

Hi Jeffrey,

Yes at the speed of this interface a serial chain of DS90LV001 devices will accumulate jitter and eventually the signal will not be recoverable by the Receiver card.

Regards,

Lee

Thank you

If the chain is designed like below, it would be OK, right?

Regards

Jeffrey

Hi Jeffrey,

You would have to ask the FPGA vendor if it is possible for them to recover this datarate in a chain of modules 200 links long.  The DS90LV001 would have no issues in this architecture.  

Regards,

Lee

OK, thank you