LMX2594: Channel divider (Phase Noise)

Hi There,

I checked my database, I have a plot with Fvco=8GHz, looks I have similar observation as yours (dark blue trace is div/8).

Looks to me that this is more or less a phase noise bump between 1kHz and 10kHz offset. I will try increasing the shunt capacitor at "Bypass' pin. For example, pin 3 is one of the bypass pins.

Hi Noel-san,

Thank you for your quick reply.

OK, I will try.

Thank you,

Arai

Hi Noel-san,

Currently, pin 3 is a 4.7uF capacitor(Ceramic).

It will be unlocked when pin 3 is set to 10uF.

Do you have any other advice.

Hi Arai-san,

10µF is the datasheet recommended value, it won't make the PLL unlock.

Please try program R0 one more time, if it is unlock.

Hi Noel-san,

I locked pin3 by sending register 0 (Re) with 10uF and 20uF.

But it doesn't improve.

Do you have any other advice.

Hi Arai-san,

Is your schematic same as EVM? 

What is your reference clock frequency; CAL_CLK_DIV setting?

Hi Noel-san,

Yes, our schematic same as EVM. (Except for the loop filter)

The reference clock frequency is 640MHz TCXO.

CAL_CLK_DIV is DIV4. fpd=160MHz

+5V_IN → LDO(ADM7151-04) → +3.3V_Vcc

Hi Arai-san,

I didn't expect your reference clock frequency is that high. What is your ACAL_CMP_DLY setting? According to TICS Pro suggestion, it should be around 16 (decimal). If it is 10, make it 16 or make CAL_CLK_DIV = Div8.

If the modified loop filter works at 160MHz fpd, it is fine.

Hi Noel-san,

ACAL_CMP_DLY setting is 16.

We will try the combination of Div8 and 10.

The result is the same for Div 8 and 10.

Hi Arai-san,

I am asking my colleague to verify this with an EVM, we will let you know the test result, stay tuned.

Hi Noel-san,

How is the findings?

If there is any good information, please let me know.

Hi Arai-san,

Unfortunately I don't have an update yet, my colleague is still waiting for green light to be able to go to the lab. We have put this test request in the queue, once we have lab access, we shall be able to get the data very quick. Sorry to keep you waiting.

Hi Noel-san,

I understand.
Thank you.