DVB_ASI stream receiving

Can you please describe this application in more detail?

I suppose you could use an LVDS fanout buffer like you proposed (or something like the DS90CP22 to get the 1:2 function), but the interface between the LMH0002 and the LVDS buffer would not be ideal.

What type of cable is used in this application?  Is the interface single ended or differential, and is the LMH0002 driving 75Ω impedance or something else?

I wonder why the LMH0002 would be used to drive the signal if the cable is indeed so short.  The LMH0002 is designed to drive a signal through long lengths of (typically 75Ω) coaxial cable so it can be properly recovered by an SDI cable equalizer on the other end.

If you want to receive the DVB-ASI stream and fanout to two outputs, you could consider the LMH0395 cable equalizer with dual outputs.  This equalizer is designed to receive the signal driven by an SDI cable driver such as the LMH0002, and can work over long lengths of cable if the cable length in this application is ever increased.

The 6.8 nH inductor in parallel with the 75Ω resistor at the input to the LMH0344 constitutes the return loss compensation network.  This return loss network compensates for the input capacitance of the receiver circuit, and is necessary to meet the SMPTE return loss requirements.  It helps to adjusts the impedance looking back into the circuit from the BNC connector to near 75Ω across the required frequency range.

Gary Melchior

Hi Gary, Thanks for the reply. The cable driven by the LMH0002 is a 75ohm coaxial cable in single end mode. The reason why the cable is so short is because originally this cable is connect to outside for external use, now we add a board internally to receive it first for local use, and then duplicate it to outside.

So will it be ok to use a SN65LVDS104 or DS90CP22 to receive it? and should we also add the 75ohm and 6.8nH matching network? 

You could use an LVDS buffer to receive the signal, but the interface would not be ideal.  You would need to configure the differential input of the LVDS buffer to receive the single-ended 75Ω signal from the LMH0002.

You do not need to include the return loss compensation network unless you are interested in meeting the SMPTE return loss requirements.  Other than helping to meet the return loss spec, it will not have a noticeable effect on performance for your application.  Please note the actual component values (i.e. 75Ω resistor and 6.8 nH inductor) are fine-tuned for the device (in this case, the LMH0344 SDI cable equalizer), so I would not recommend using these with one of the LVDS buffer devices.

I believe DVB-ASI also has a return loss requirement (15 dB min return loss from 300 kHz to 1 GHz).  If you are interested in meeting this return loss spec for you receiver input, I would recommend to use an SDI / DVB-ASI cable equalizer such as the LMH0044, LMH0344, or LMH0395 (the latter also provides you with the 1:2 function).

Gary Melchior

Hi Gary, in this case I may consider to use LMH0344 to receive it and SN65LVDS004

to duplicate it, will it be Ok? since these two ICs already used in our other boards and 

easy to get.

Hi Gary, thanks a lot.