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LMX1214: Minimum Operating frequency

Tom Armitage
Prodigy 20 points
Part Number: LMX1214
Other Parts Discussed in Thread: LMX1204, LMX1205,

Tool/software:

Hello,

The data sheet for the LMX1214 and related devices such as LMX1204, LMX1205 all list a minimum operating frequency of 300MHz.

We have an application where we want to distribute a 200MHz clock from a 200MHz source.   

Will these devices work at 200MHz?

The specifications for these devices look good, except for the 300MHz minimum operating frequency.

Can the devices be set to "bypass mode" ie no multipliers/dividers and operate at 200MHz? 

Multipliers and dividers are not functionality that we require.

We are not necessarily interested in using the SYNC / AUXCLKOUT functionality either.

Does TI have any other devices with similar specifications (ie additive jitter, noise floor and output skew) that will operate at 200MHz?

Regards,

Tom 

  • 0
    TI__Mastermind 29172 points

    Hello Tom, 
    LMX series parts usually are CML outputs only. 
    The buffer we have with the lowest noise floor is LMK1C family, but these are LVCMOS buffers. 

    I have heard that previously the LMX buffers work at lower frequencies but only if the input swing is high enough. I will loop in the AE responsible for this part - he could answer more related to using LMX1214 at lower frequencies. 

    We also have LMKDB family which are LP-HCSL buffers targeted for PCIe ref clk fan out applications but the noise floor is worse than LMK1C. 
    We also have LMK1D which is similar to LMKDB family but the output format is LVDS instead. 

    Best regards, 

    Vicente 

  • 0 in reply to vicente flores prado
    TI__Guru** 107830 points

    Hi Tom,

    At 200MHz, you may consider LMK1C, which is a high performance CMOS buffer.

    If you need better performance, LMX1214 is the simplest RF buffer we have.

    I did a quick check, LMX1214 can support 200MHz operation.

    Below is the output phase noise of LMX1214. Light blue is with 300MHz input, dark blue is with 200MHz input. 

  • 0 in reply to Noel Fung
    Prodigy 20 points

    Hello Noel,

    Thanks for that information it is very helpful. 

    Can you explain why the LMX1214 is specified at 300MHz if it works with a 200MHz input?  Are there any potential limitations / functionality that won't work at with a 200MHz input clock?  Is it the case that it just hasn't been characterised at 200MHz?

    Is it possible to operate the LMX1204 in "buffer mode" (ie bypass all PLL, multipliers, dividers etc so it is more like the LMX1214) at 200MHz?  If so, should we expect to see similar performance from the LMX1204 operating as a buffer at 200MHz as you'd expect from the LMX1214 at 200MHz?   

    The reason I ask is we can only easily find the LMX1204 evaluation board, but the LMX1214 is the device we are interested in.

    Thanks again,

    Tom

  • 0 in reply to vicente flores prado
    Prodigy 20 points

    Hi Vicente,

    Thanks for your reply, I will take another look at some of those devices.  Ideally we'd prefer a differential clock buffer with fast outputs.

    Cheers,

    Tom 

  • 0 in reply to Tom Armitage
    TI__Guru** 107830 points

    Hi Tom,

    I am checking this out with the team, I believe the device can support 200MHz without questions. Our sales guys will contact you soon to help you get the eval board. 

  • 0 in reply to Noel Fung
    Prodigy 20 points

    Thanks, I am keen to get an eval board for the LMX1214 if one is available.