LMX1214: CLKOUT usage

Nandini Muralidharan

Part Number: LMX1214

Tool/software:

Hi,

The input frequency to clock buffer is 1800MHz and we plan to connect CLKOUT pins to FPGA and set them at output frequency of 225MHz.

The CLKOUT pins seem to be similar to CML standard. FPGA can support LVDS as below:

It also supports below highlighted differential standards.

So, can you please share which standard to use at FPGA's input side to meet CLKOUT's output standard?

Also pls recommend what type of termination needs to be used between these two interface standards?

Thanks

5 months ago

0 Noel Fung 5 months ago

TI__Guru* 97220 points

Hi Nandini,

CLKOUT requires AC-couple, so you should use the LVDS interface.

CLKOUT also requires 50Ω termination at the receiver end.

0 Nandini Muralidharan 5 months ago in reply to Noel Fung

Intellectual 750 points

Hi Noel,

Do you mean like this?
100 ohm parallel termination between P & N signals. And external biasing termination resistors at RX end?

0 Noel Fung 5 months ago in reply to Nandini Muralidharan

TI__Guru* 97220 points

Hi Nandini,

You'd better ask your FPGA vendor to confirm.

0 Nandini Muralidharan 5 months ago in reply to Noel Fung

Intellectual 750 points

Hi Noel,

I will confirm with FPGA vendor on this.

However can you share from clock buffer's perspective, if 100-ohm differential between P & N is ok instead of the 50-ohm termination (presumably to GND) that you were suggesting?

0 Noel Fung 5 months ago in reply to Nandini Muralidharan

TI__Guru* 97220 points

Hi Nandini,

differential 100Ω is better, especially good for pcb layout.

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LMX1214: CLKOUT usage