How to calculate Capacitor value for AC Coupling.

[mhm00]

I'm using Cyclone V 5CGXFC5C6F23I7N FPGA.

In Transceiver section,the clock for the REFCLK is provided by External OSCILLATOR and its frequency is 125MHz, LVDS IO Standard,and I'm using AC COUPLING,for AC Coupling we need capacitor,so when I start to find the value of the capacitor I understand that I need to know the INPUT IMPEDANCE at the dedicated REFCLK PINS of the FPGA, but I didn't found the information about INPUT IMPEDANCE at the at the dedicated REFCLK PINS.

so what would be the INPUT IMPEDANCE at the dedicated REFCLK PINS of theCYCLONE V FPGA?

[Nathan_R_Intel]

Hie,

Apologies for the delayed first response. The typical response time is within 24 hours, but this case was assigned to me and it was a delay from my part to provide response in time.

The Input Impedance of the dedicated REFCLK pins of the FPGA is 100ohms. This is available in the datasheet

Refer to Table 21, listed as ON-chip termination resistors)

https://www.intel.com/content/dam/www/programmable/us/en/pdfs/literature/hb/cyclone-v/cv_51002.pdf

I hope this answers your question. Do let me know, if you have further question, I will provide an update as soon as possible.

Regards,

Nathan

[mhm00]

Thank you for the support.

[Nathan_R_Intel]

Sure.