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Soft LVDS aligned output clock


Hello! I am looking for help with a SERDES setup using Quartus. First a brief problem description and then I will provide more details below.


The 10-to-1 serializer is driven with two external clocks. I am feeding the input on the rising edge of the slow clock and 400ns later (in ModelSim at least) I get the serialized output out of Altera's Soft LVDS block. Each individual output state is aligned with the fast clock, but I do not see any output clock that I can use to tell the receiver when a new block of data begins. Where do I get a slow clock signal that's aligned with the SERDES output frame?




Boring details:

I am new to FPGAs and after completing a number of tutorials I found this nice HDMI one here:

As far as I can tell the signal generation for the three 10-bit channels is working fine, the last piece is getting those channels serialized and sent via the dedicated LVDS pins of the Altera MAX 10 that I am using.

I am using an ALTPLL block to create the basic signal clock C0 and a secondary C1 clock which is 5 times faster (according to Soft LVDS documentation). Each channel goes into an Altera LVDS instance (configured for external PLL) along with the two clock signals. Running the whole thing in ModelSim I see the expected data going in an coming out. The problem is, where can I grab a clock that is synchronized to the LVDS output? Can I rely on the simulation and add a 400ns delay or add another slow clock output with a 144 degree phase shift? Those ideas don't sound too great, so what is the recommended solution?

(Note: this is not the final clock speed, I am trying to slow things way below HDMI specs just so I can confirm waveforms on my slow oscilloscope)

Quartus project folder:

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3 Replies
Hello Marco , Thank you for the detailed explanation , Sorry for late reply , i was caught into other stuff As per the Max 10 LVDS Serdes user guide , fast clock input should connect to the c0 and slow clock connect to the c1, but in your design it is vice versa. Coming back to your question , You can use the loaden signal to mention the receiver your new set of the data begins. isnt it slow clock is already aligned with your data ? I am not sure where iam missing out in your design. thank you , Regards, Sree

Hello Sree,

Thank you for your response!


"isnt it slow clock is already aligned with your data ? I am not sure where iam missing out in your design."

The slow clock is correctly aligned with the incoming parallel data.

What I am looking for is some kind of framing signal for the outgoing serialized data (where does the 1st bit of the outgoing stream start?)


When using LVDS Serdes with its own internal PLL it generates an outgoing slow clock. When using LVDS Serdes with the external PLL I do not see any option to get an outgoing clock though

Hello Marco , About your second question.. Can you refer the Figure 2 in the below link , Block diagram clearly show how to connect the external i.e ATLPLL to the transmitter and receiver core clock . I dont think so you need a external clock out from transmitter, Receiver can generate there own reference clock and phase aligns with data stream. First question : Can you tell me in HW connection in your board are you having clock from transmitter to receiver ? Thank you , Regards, Sree