LMK00308: AC coupling the LVDS output

Mark Dahlman

Intellectual 2025 points

Part Number: LMK00308
Other Parts Discussed in Thread: LMK00304,

Figure 34 in the datasheet shows how to AC couple the LVDS output when used with a device with internal termination resistors. The issue with this is that the LVDS signal is attenuated by the double termination. I noticed in another e2e post on the LMK00304 that a minimum DC termination of 1K ohms was needed to ensure startup of the LVDS driver. Can the 100 ohm near end DC termination resistor in figure 34 be increased to 1K ohms on the LMK00308 when AC coupling the output to reduce the overall attenuation from the double termination?

Thanks for your help,

Mark Dahlman

over 2 years ago

0 Noel Fung over 2 years ago

TI__Guru* 92420 points

Hi Mark,

If you are referring to below post, Alan suggested a 1kΩ across the terminals.

https://e2e.ti.com/support/clock-timing-group/clock-and-timing/f/clock-timing-forum/722839/lmk00304-input-lvds-ac-coupling?tisearch=e2e-sitesearch&keymatch=lmk00304#

0 Mark Dahlman over 2 years ago in reply to Noel Fung

TI__Intellectual 2025 points

Yes, that's what I am referring to. Can I place 1K across the output terminals, AC couple the differential pair, send the signal down a 100ohm transmission line, and then use the internal 100 ohm termination inside my FPGA.

0 Noel Fung over 2 years ago in reply to Mark Dahlman

TI__Guru* 92420 points

Hi Mark,

Yes, I think the resistor could be between 560Ω to 1kΩ.

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LMK00308: AC coupling the LVDS output