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Visitor
Visitor
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Registered: ‎11-05-2018

SDI IP Core Ref Clock

Hi,

I use XC6SLX25T-3CSG324I and I want to use Triple-Rate SDI IP Core.

The questions are about GTP External Reference Clock.

1. I can't find the suitable external Oscillator Frequency Stability (in ppm) for 3G-SDI. What is the range of Frequency Stability for 3G-SDI?

2. How many External Oscillator I need for below scenario.(Do I only need a 74.25MHz or 148.5MHz REFCLK0 or need both of them at the same time on REFCLK0 and REFCLK1?).

The XC6SLX25T-3CSG324I has two MGTRXx and always the SDI inputs for each of them is different from the other. I will have these 3 states:

S1:

MGTRXx0: 3G-SDI

MGTRXx1: HD-SDI

 

S2:

MGTRXx0: 3G-SDI

MGTRXx1: SD-SDI

 

S3:

MGTRXx0: HD-SDI

MGTRXx1: SD-SDI

Thanks.

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5 Replies
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Moderator
Moderator
316 Views
Registered: ‎04-09-2019

Hello @routed ,

The Required reference clock frequency for QPLL's of GTP Transceiver is 148.5 Mhz. In the down stream the GTP will generate the RX OOUCLK and TXOUTCLK frequencies based on the mode detected. So, Most Probably for Your use case 148.5 Mhz reference clock frequency is required.

Hope this Information is helpful to You.

With Regards,

Ashok.

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Visitor
Visitor
283 Views
Registered: ‎11-05-2018

Hi @ashokkum 

Thanks for quick reply.

Is there any answer for my first question?(1. I can't find the suitable external Oscillator Frequency Stability (in ppm) for 3G-SDI. What is the range of Frequency Stability for 3G-SDI?)

Thanks

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Highlighted
Moderator
Moderator
221 Views
Registered: ‎04-09-2019

Hello @routed ,

Most Probably, SDI data rates won't require a PPM. It is more about related to GT Transceivers. Hopefully the PPM would be different for different GT Transceivers.

 

With Regards,

Ashok.

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Explorer
Explorer
199 Views
Registered: ‎07-18-2011

 

@routed 

You only need one reference clock to receive all SDI formats, but you will need two reference clocks to be able to transmit all SDI formats, a148.5 MHz refclock for the 1000/1000 formats (60Hz/50Hz), and a 148.5/1.001 MHz refclock for the 1000/1001 formats (59.94Hz and 29.97Hz).

If you are only transmitting the 1000/1000 formats, you can get by with a single 148.5MHz reference clock shared between all receivers and transmitters. 

The main thing you need to worry about with SDI clocking is jitter.   If you select a good ultra-low jitter clock source designed for SDI, the frequency stability of the part will generally be low enough as well.  

Silicon Labs has many excellent parts suitable for 3G-SDI and higher rates:

https://www.silabs.com/timing/oscillators

https://www.silabs.com/timing/clock-generators

They also have several app notes on clocking jitter, such as the one listed below.   See pages 11 and 12 for jitter limit specifications for SDI:  

https://www.silabs.com/documents/public/application-notes/AN377.pdf

 

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Moderator
Moderator
117 Views
Registered: ‎04-09-2019

Hello @routed ,

The GTP PPM spec is described in DS181 table 58. For REFCLK static ppm, refer to the RXppmtol line which is +/- 1250 ppm. The same attached below. Kindly find it.

Hope it would be helpful to You.

With Regards,

Ashok.

image.png