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LMK61E08: Recommended Oscillator

Shuji Ishiwata
Mastermind 6115 points
Part Number: LMK61E08
Other Parts Discussed in Thread: LMX2820, , LMK05318, LMK05028, LMK05318B, LMK61E2, LMK6P

Tool/software:

Hi All,


A customer is considering LMX2820.
We are currently taking measures to reduce phase noise.
Among them, we are considering TI's oscillator for input to OSCIN_P/N.
Please tell me the recommended oscillator that can be used with LMX2820.
The desired specification is an oscillator that can be synchronized with an external input of 144MHz.

Initially, I contacted LM2820 Clock & timing forum and they suggested the LMK61E08.
Customers reported that the LMK61E08 had slightly worse VCO phase noise.

Don’t you think BAW type devices such as LMK05028 or LMK05318 provides better phase noise performance than LMK61E08 or can you let me know better option than LMK621E08 .

I received a comment in the following E2E to contact Hannes Estl:
https://e2e.ti.com/support/clock-timing-group/clock-and-timing/f/clock-timing-forum/1361894/lmk6c-oscillator-input-to-lmx2820/5222715#5222715　


Best Regards,
Ishiwata

  • 0
    TI__Expert 7110 points

    Hi Ishiwata, 

    How many 144 MHz clocks do you need in your system? If you need several then it may be worth considering using a clock generator or jitter cleaner that can generate multiple output clocks. In this case, the BAW network synchronizers such as LMK05318B or LMK5B wouldn't be suitable for generating 144 MHz outputs since the BAW VCO is fixed at 2500 MHz and must have an integer relationship with the output frequency.

    The LMK6x family of oscillators has the performance advantages of BAW plus a fractional output divider to reach any output frequency between 1-400 MHz. Here's a link to the device datasheet for reference: https://www.ti.com/lit/ds/snas826e/snas826e.pdf 

    We haven't released a 144 MHz variant of LMK6x yet, but we can provide a small quantity of samples that we program manually for initial evaluation. I don't have any phase noise or jitter measurements at 144 MHz yet, but I can collect some tomorrow or early next week to compare with LMK61E2. 

    Regards, 

    Connor 

  • 0 in reply to Connor Lewis
    Mastermind 6115 points

    Hello Connor,


    Thank you for your reply.
    I checked the phase noise characteristic data of the LMK6x you proposed.
    The LMK61E08, which I initially recommended and proposed to the customer, has better characteristics.

    LMK6x

    LMK61E08

    I have determined that it will be difficult to improve phase noise with TI's BAW products.
    Thank you for your support.


    Best Regards,
    Ishiwata

  • 0 in reply to Shuji Ishiwata
    TI__Expert 7110 points

    Hi Ishiwata, 

    Can you explain a bit more about what your phase noise requirements are at different offsets? LMK6x has better phase noise performance compared to LMK61 at certain intervals, so it depends which range is most important for your application. I also collected some phase noise measurements at 144 MHz for these devices to see a real world comparison, plus an overlay of the two phase noise curves:

    LMK6P 144 MHz:

    LMK61E2 144 MHz:

    Overlay:

    Let me know if this is helpful. 

    Regards, 

    Connor