LMK00304

Jim George

Other Parts Discussed in Thread: LMK00304, ONET1191P

I'm interested in using an LMK00304 to distribute a 100 MHz sinewave clock to three separate PLLs. The 100 MHz clock originates from a GPS-disciplined OCXO, with very good phase noise properties (-160 dBc/Hz floor, -140 dBc/Hz at 1k offset).

In one of the videos produced by TI regarding phase noise and jitter measurement on clock buffers, there's a mention of using an amplifier and limiter (the video shows a number of connectorized parts) to improve the rise time of a 100 MHz OCXO. Would anyone be able to share how this is done, and what kind of slew rates can be achieved with this setup? A quick back-of-the-envelope calculation using a Mini-circuits RLM-33+ limiter (+10 dBm out, +20 dBm in) indicates that I should get about 2 V/ns, which is still shy of the 3 V/ns that the LMK00304 needs for optimum performance. What other options do I have to improve the slew rate?

What about a device like the ONET1191P? Would its jitter be worse than that of the LMK00304? I see that the jitter spec is about 0.4 ps, which is quite high compared to the additive jitter of the clock buffer.

Thanks in advance.

over 11 years ago

0 Alan O over 11 years ago

TI__Mastermind 32575 points

Hi Jim,

3 V/ns is the differential input slew rate for optimum performance. This is 1.5 V/ns slew rate measured single-endedly on P and N inputs.

So, uou could try adding a balun to the output of your RLM-33+ limiter.

Here's the bench setup we used for achieving a high-slew-rate differential input signal:
Low-noise 100 MHz OCXO (+15dBm) -> VLM-33+ limiter (+13 dBm o/p) -> MACOM H-183-4 (single-ended to differential) -> DUT

Regards,
Alan

0 Jim George over 11 years ago in reply to Alan O

Prodigy 100 points

Thanks, Alan.

I have a number of surface-mount baluns that seem suitable for use here. Mini-circuits' TC1-1-13M+ seems like a good candidate (equivalent of Macom's ETC1-1-13).

Thanks again for your help!

0 Alan O over 11 years ago in reply to Jim George

TI__Mastermind 32575 points

Hi Jim,

No problem. Just curious, if you don't mind me asking, what is the end-equipment/application for this GPS disiciplined OCXO + SMT balun + LMK00304 fanout buffer which requires this ultra-low phase noise requirement?

Regards,
Alan

0 Jim George over 11 years ago in reply to Alan O

Prodigy 100 points

Hi Alan,

The fanout buffer drives a set of PLLs that generate local oscillator signals for a weather radar at S-band. Multiple PLLs are used so that they may be selected using an RF switch to do frequency hopping. Each PLL has a narrow-band coaxial resonant VCO, so the reference jitter > 1 MHz from the carrier is not too critical.

Thanks!

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LMK00304