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Observer
Posts: 21
Registered: ‎02-24-2011

Clocking GTX Quad from KC705's Si570

Hi,

 

being not so familiar with (SI and FPGA-related) physical restrictions conserning clocks, I have a question about clocking the GTX Quad on the Xilinx Kintex-7 KC705 board.

 

The board has Si570 ("Si570 3.3V LVDS I2C Programmable Oscillator") routed to:

NET USER_CLOCK_P LOC = K28 | IOSTANDARD=LVDS_25; # Bank 15 VCCO - VCC2V5_FPGA - IO_L13P_T2_MRCC_15
NET USER_CLOCK_N LOC = K29 | IOSTANDARD=LVDS_25; # Bank 15 VCCO - VCC2V5_FPGA - IO_L13N_T2_MRCC_15

 

On the same bank there are signals routed to SMA-connectors on the board (for clock input):

NET USER_SMA_CLOCK_P LOC = L25 | IOSTANDARD=LVDS_25; # Bank 15 VCCO - VCC2V5_FPGA - IO_L12P_T1_MRCC_AD5P_15
NET USER_SMA_CLOCK_N LOC = K25 | IOSTANDARD=LVDS_25; # Bank 15 VCCO - VCC2V5_FPGA - IO_L12N_T1_MRCC_AD5N_15

 

Am I able to drive the clock signal out to these SMA-connectors and connect them to the SMA GTX clock in SMA connectors on the board (wired to GTX Quad bank 117)? If not, why (SI / jitter related?)?

The Si5326 jitter attenuator on the board is maybe targeted for this kind of use (routed to the GTX Quad 116)? But I suppose there isn't a easy way to program it..? And also that it doesn't power on to some default state that would be usable, or?

I'm trying to get a 150MHz clock for Aurora core for SFP (on the GTX Quad 117) with Aurora IP Core connection .

KC705 User Guide:
http://www.xilinx.com/support/documentation/boards_and_kits/ug810_KC705_Eval_Bd.pdf
KC705 Schematic:

http://www.xilinx.com/support/documentation/boards_and_kits/kc705_Schematic_xtp132_rev1_1.pdf

Observer
Posts: 21
Registered: ‎02-24-2011

Re: Clocking GTX Quad from KC705's Si570

Ah, the Kintex-7 GTX Quad's have a clock input pin named GTGREFCLK, which is possible to be driven by FPGA logic:

 

GTGREFCLK / In / Clock / Reference clock generated by the internal FPGA logic. / This input is reserved for internal testing purposes only.

 

http://www.xilinx.com/support/documentation/user_guides/ug476_7Series_Transceivers.pdf

 

I suppose this is supported by the ISE? Is it better to route the Si570's clock through the fabric to this pin, or through the SMA-connectors? Or am I doomed regardless? 

Visitor
Posts: 4
Registered: ‎12-06-2011

Re: Clocking GTX Quad from KC705's Si570

I was faced with the same problem. I think you can use the SGMII clock that's also on bank 117 for the SMA.