LMK61E0-050M: Output impedance and termination

Lucas C

Part Number: LMK61E0-050M
Other Parts Discussed in Thread: CDCLVP1204

Hi,

The datasheet shows that for LVPECL termination there should be a 150-ohm resistor to GND, however, that is if you are probing the signal with a high-impedance probe. Given that I will route this signal with a 50-ohm transmission line to an LVPECL input, what should be the external resistor to match the output of the LMK61E0-050M to a 50-ohm transmission line? Would it be referred to Vcc?

I will be connecting the output of the LMK61E0-050M to the input of a CDCLVP1204, and as I'm using 3.3 V as Vcc, I'll be terminating the transmission line with a pull-up of 130 ohms and a pull-down of 82 ohms to get the 50-ohms termination at Vcc - 2 V.

Thanks.

over 4 years ago

0 Lane Boyd over 4 years ago

TI__Genius 16845 points

Hi Lucas,

This termination network is correct for 3.3V LVPECL.

Kind regards,
Lane

0 Lucas C over 4 years ago in reply to Lane Boyd

Prodigy 70 points

Hi Lane,

Thanks for the reply.

The termination will be on the side of the CDCLVP1204 to match the input impedance of the part and get the correct logic levels, but I'm still a bit confused about whether the output of the LMK61E0-050M needs any external resistors to get the correct impedance and logic levels before going into the 50-ohm transmission line. I'm asking because, in the test schematic (on the datasheet) the output is terminated on two 150-ohm resistors, which makes me think that I'll see different logic levels compared to a 50-ohm termination to Vcc -2 V.

Thanks.

0 Lane Boyd over 4 years ago in reply to Lucas C

TI__Genius 16845 points

Hi Lucas,

With this receiver side termination, you do not need any driver side termination (150ohm to GND is not needed)

Kind regards,
Lane

0 Lucas C over 4 years ago in reply to Lane Boyd

Prodigy 70 points

Hi Lane,

Thank you for confirming it.

Clock & timing

Clock & timing forum

LMK61E0-050M: Output impedance and termination