LMK03318: differential output clock design question

user4943534

Prodigy 50 points

Part Number: LMK03318
Other Parts Discussed in Thread: LMK00304,

Hi TI pals,

I plan to use LMK03318 for clock source and buffer LMK00304 to fanout clock for low phase jitter device requirement.

I get some suggestion design as below.

LMK03318_P to AC CAP_P1 to node_P to AC CAP_P2 to LMK00304_P

LMK00318_N to AC CAP_N1 to node_N to AC CAP_N2 to LMK00304_N

Between node_P and node_N add 100ohm resistor.

I don't understand about twice AC coupling design.

Does someone help to explain two AC coupling function?

Thanks

Allen

over 6 years ago

0 Alan O over 6 years ago

TI__Mastermind 32575 points

In this case, it is possible to eliminate the AC coupling caps for the driver since the receiver inputs are already AC coupled.
For example:
OUT_P/N --> 50-ohm traces --> Input termination (100 ohm differential close to CLKIN pins) --> AC-coupling cap --> CLKINx_P/N (internal weak biasing)

Alan

0 user4943534 over 6 years ago in reply to Alan O

Prodigy 50 points

Hi Alan,

My question is why the suggestion is twice AC coupled on external circuit.
Although LMK00304 do not mention internal AC coupled and only DC bias on input.

Thanks
Allen

0 Alan O over 6 years ago in reply to user4943534

TI__Mastermind 32575 points

I did not suggest to have two sets of AC caps. My suggestion was to have only one set of AC coupling caps (between the receiver's input termination and input pins).

Alan

Clock & timing

Clock & timing forum

LMK03318: differential output clock design question