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LMK04832-SP: LMK04832-SP vs. LMX2615-SP

Part Number: LMK04832-SP
Other Parts Discussed in Thread: LMX2615-SP, , LMX2594, LMK04832, LMX2592, LMX2572

What are the differences between the LMK04832-SP and LMX2615-SP and can I use each to generate the following:

 

1. Phase-coherent 750 MSPS and 6 GSPS clocks

2. Phase-coherent 3 GSPS and 6 GSPS clocks

thank you,

Rajan

  • Hi Rajan,

    Both can generate <3GHz clock output and sysref for deterministic delay. However, LMX2615-SP is a space-grade part. If you do not plan to use it in space applications, you can consider the LMX2594, or the upcoming LMX2694.

    LMK04832-SP is primarily used as jitter cleaner and clock generator. It has dual loop architecture for the purpose of jitter cleaning (first loop) and frequency planning/clock generation (second loop). It can generate multiple clock outputs in various formats.

    LMX2594/2595/2615 are primarily used as RF synthesizer and sometimes high speed clock as well. Outputs of LMX2594/2615 can go up to 15GHz, but it only has two outputs. If you want to use SYSREF then there's only one output available. So you might want to use LMK04832/4828 if you only need up to 3GHz clock output.

    I'm attaching some TI selection guides for your reference.

    Dual loop jitter cleaner: www.ti.com/.../products.html

    Network synchronizer: www.ti.com/.../products.html

    RF synthesizer: www.ti.com/.../products.html

    Regards,
    Hao

  • I need to generate two phase-locked clocks:

    Case 1: 750 MHz and 6 GHz
    Case 2: 3 GHz and 6 GHz

    Would you recommend LMK04832-SP or LMX2615-SP?

  • LMK04832-SP only supports up to 3255MHz output frequency. So use LMX2615-SP.

    Regards,
    Hao

  • Thank you Hao

    Can I command/control the LMX2615-SP using an FPGA to output two phase-locked outputs at 750 MHz and 6 GHz?

    Can I command/control the LMX2615-SP using an FPGA to output two phase-locked outputs at 3 GHz and 6 GHz?

    Kind Regards,
    Rajan.
  • these clocks will be used to drive an ADC and DAC
  • Hi Rajan,

    Sorry the previous answer was wrong. You need a part whose VCO frequency can hit 6GHz, because for LMX parts there is only one output divider for both outputs. So you need a direct VCO output for one port, and then divided down version for the other.

    So for these two cases, available solutions are LMX2572 and LMX2592.

    For case 1, you can do direct VCO for 6GHz output, then divide-by-6 for 750MHz output.
    For case 2, you can do direct VCO for 6GHz output, then divide-by-2 for 3GHz output.

    Regards,
    Hao
  • I need a space-grade part, are you saying that neither the LMK04832-SP or the LMX2615-SP will output my desired locked frequencies?

  • Hi Rajan,

    In that case you can only use one LMK04832-SP and one LMX2615-SP for each of the output.

    Regards,
    Hao

  • If I use both devices together, will their outputs be phase-locked?
  • The output of a PLL is locked to the input for sure. Are you looking for something like deterministic delay?

    Regards,
    Hao
  • I have one other question for now:

    Could I also use either of these devices to delay a 750MHz or a 3 GHz clock by 270 degrees?
  • Hi Rajan,

    For LMX2615-SP yes, you can check out the MASH_SEED in the datasheet. But note that this delay is with reference to its original position.

    For LMK04832 I'm not sure. If you'd like to get into more details, please post a separate question on LMK04832 and our LMK experts will answer that.

    Regards,
    Hao
  • Hao,

    The LMX2615 offers two RF outputs, would you be available for a short telephone conversation as this would be easier.

    Kind Regards,

    Rajan

  • Hao,

    Can multiple LMX2615s be locked together to provide phase-coherent outputs?

    for project one, can the LMX2615 output a 750 MHz clock and another at the same frequency delayed by 1 ns
    also for project one, can he LMX2615 output a 3 GHz clock and another at the same frequency delayed by 250 ps

    for project two, can the LMX2615 output locked 750 MHz and 6 GHz clocks
    also for project two, can the LMX2615 output locked 3 GHz and 6 GHz clocks

    thank you
  • Hi Rajan,

    Have you reached out to a local FAE? Can you ask the FAE to generate a thread on "helpme" system and set up a call with Dean Banerjee and myself? Dean is the expert on LMX2615. Let me know if you still prefer writing on E2E and I'll answer the questions.

    Regards,
    Hao
  • Hao,

    It would really help me a lot if you could answer the questions in my previous message please.

    I will then decide how best to proceed.

    Kind Regards,
    Rajan
  • Hi Rajan,

    Yes multiple LMX2615 devices can have phase synchronized outputs using the "SYNC" feature.

    Almost arbitrary time delay / phase shift can be generated using "MASH_SEED". So 1ns and 250ps delay is not a problem.

    Please check out the "SYNC" and "MASH_SEED" in datasheet for more details.

    Note that although LMX2615 has two outputs available, it CANNOT generate 750MHz and 6GHz at the same time. As I explained earlier, there is only one output divider for both of the outputs, so the combination of 750 and 6 is not possible, neither is 3 and 6. You'll still need a LMK04832 to generate the 750 and 3GHz signals.

    Regards,
    Hao
  • Hao,

    Therefore I would have to use LMX2615 to generate the 6 GHz output and the  LMK04832 to output either 750 MHz or 3 GHz.

    Can both devices be phase locked to one another?

    Kind Regards,

    Rajan.

  • Hao,

    Could I use the LMK04832 to generate all of the following clocks:

    1. 750 MHz
    2. 750 MHz delayed by 1ns
    3. 50 MHz
    4. 250 MHz
    5. 3 GHz
    6. 3 GHz delayed by 250 ps

    Will the LMK04832 allow me to enable/disable specific outputs?

    Kind Regards,
    Rajan.
  • Hi Rajan,

    Yes LMK04832 can generate all 6 outputs. 250ps and 1ns delay can be achieved by using analog delay and digital delay.

    LMK04832 allows user to enable/disable every individual output.

    Multiple LMX2615 or LMK04832 devices can be phase locked to the same reference source in order to generate phase-correlated outputs.

    Regards,
    Hao
  • this is excellent, thank you very much Hao

    the plan is to use the LMK04832 to generate the 6 outputs and the LMX2615 to output 6 GHz.

    For the LMK04832, will the 6 outputs be phase-locked?

    How do I phase lock the 6 GHz output from the LMX2615 to the LMK04832?

  • Hi Rajan,

    Yes the 6 outputs of LMK04832 will be phase locked to the same reference with zero delay. You can check out "0 delay" feature in the datasheet.

    You can simply have LMK04832 and LMX2615 share the same source.

    "Phase lock" is used to describe the phase relationship between reference input and VCO output, so you cannot say that one output is phase locked to another. The right way of seeing this is that both outputs are phase locked to the same source. And as explained above, this can done easily by having them share the same source.

    Regards,
    Hao
  • Hao,

    To produce 250 MHz, 750 MHz and 3 GHz outputs from the LMK04832, should this input source frequency be a specific value?

    Both the LMK04832 and the LMX2615 output differential outputs so I can a.c. couple these directly to an ADC and FPGA and will not need baluns.

    Kind Regards,
    Rajan.
  • Hi Rajan,

    You can use any input frequency within the boundary of datasheet spec. However, to make 0 delay easier, you may set the input to a common divisor of all three outputs, such as 250MHz, 125MHz and so on.

    Regards,
    Hao
  • Hi Hao,

    Hope you are well.

    My intention is to use the LMK04832 to generate the six system frequencies and then output a duplicate of either the 750 MHz or 3 GHz as the input to the LMX2615 to also generate a phase-locked 6 GHz output clock.

    I have noticed that the only way to disable/enable individual outputs from the LMK04832 is via the group VCC pins.

    For both the LMK04832 and the LMX2615, what would be their maximum power consumptions?

    Kind Regards,

    Rajan.

     

     

  • Hao,

    I have noticed an error in the LS2615 datasheet, pins VCCDIG and VCCMASH are not connected to Vcc, both capacitors are floating.

    Kind Regards,
    Rajan.
  • Hi Rajan,

    You are absolutely correct. That schematic in the datasheet was messed up. We'll fix that in next revision. Please refer to the schematic in user's guide for now. www.ti.com/.../snau218.pdf

    Regards,
    Hao
  • Sorry I didn't see the previous question. For LMK04832, there should be registers CLKoutx_FMT (for example, CLKout3_FMT) that have "powerdown" option.

    LMK04832 provides max current for some use cases: 

    Simply multiply that number by supply voltage to get max power consumption.

    I'm afraid LMX2615 doesn't guarantee max current. Only typical values are provided.

    Regards,

    Hao

  • thank you very much Hao, can both devices be controlled using SPI as the design does not have sufficient I/O to support parallel I/O.

    for the LMX2615, if I use the SPI, can the FSx pins be left floating

  • Hao,

    Thank you for your support.

    I have started to enter a schematic for both parts which I would like to send to you shortly? I have the following questions please:

    1. Can the LMK04832 output a 3 GHz differential clock, a.c. couple and then input this to the LMX2615 to produce a phase-coherent 6 GHz output?

    2. Can I directly a.c. couple the differential 6 GHz output from the LMX2615 to supply a DAC with its differential clock input?

    3. For the LMX2615, it's odd that VIH max for the digital control inputs is 1.6V max. Are both devices intended to interface with 1V8 logic, i.e. SPI interface and CS.

    4. Can I use a FPGA to control both devices via SPI?

    I have to enter the loop filters and a input reference source to the LMK04832, and then would like to share my schematic sheet with you please for any obvious errors

    thank you,
    Rajan.
  • Hao,

    I have one other question please: the LMK04832 contains an internal VCO which I would prefer to use rather than external reference: if I use its internal reference, will I be able to generate outputs at 250 MHz, 750 MHz, 3 GHz and delayed versions of 750 MHz and 3 GHz. Will the internal VCO have to be set to a specific frequency to produce the desired frequencies?

    thank you,
    Rajan.
  • Dear Hao,

    You have provided such wonderful feedback, would it be possible to speak by phone to allow me to re-risk both parts please?

    Kind Regards,
    Rajan.
  • Hi Rajan,

    Sorry for the delay, I was out of office. I'll answer those questions soon. Can I contact you with the email address you used for "myTI" account?

    Regards,
    Hao
  • Hi Rajan,

    For question:

    can both devices be controlled using SPI as the design does not have sufficient I/O to support parallel I/O.

    for the LMX2615, if I use the SPI, can the FSx pins be left floating

    Yes both devices support SPI. Check out "Pin functions" table for more information.

    Check out table 11 for pin connections when unused.

  • For questions:

    1. Can the LMK04832 output a 3 GHz differential clock, a.c. couple and then input this to the LMX2615 to produce a phase-coherent 6 GHz output?

    2. Can I directly a.c. couple the differential 6 GHz output from the LMX2615 to supply a DAC with its differential clock input?

    3. For the LMX2615, it's odd that VIH max for the digital control inputs is 1.6V max. Are both devices intended to interface with 1V8 logic, i.e. SPI interface and CS.

    4. Can I use a FPGA to control both devices via SPI?

    I have to enter the loop filters and a input reference source to the LMK04832, and then would like to share my schematic sheet with you please for any obvious errors

     

    1. No. Check out max reference frequency on page 8.

    2. If the DAC has internal biasing then it's fine, only one decoupling capacitor is needed between the output of LMX2615 and DAC. Note that pull up resistors/inductors are needed for the output of LMX2615. Refer to the datasheet for details of output configuration.

    3. This one I'm not sure. I'll get back to you tomorrow.

    4. Yes.

    You can use PLLatinum sim to design your loop filter: http://www.ti.com/tool/PLLATINUMSIM-SW?keyMatch=pllatinum%20sim&tisearch=Search-EN-Products

    Regards,

    Hao

     

  • For question:

    the LMK04832 contains an internal VCO which I would prefer to use rather than external reference: if I use its internal reference, will I be able to generate outputs at 250 MHz, 750 MHz, 3 GHz and delayed versions of 750 MHz and 3 GHz. Will the internal VCO have to be set to a specific frequency to produce the desired frequencies?

    I don't quite understand this one. Yes it has internal VCO for PLL2 but it doesn't have internal reference. User still needs to provide external reference.

    Regards,

    Hao

  • I'll set up a call if you are OK with me sending message to the email address you used for registration of "myTI". I need your permission before sending anything to you according to TI policy.

    Regards,
    Hao
  • Please do email me so we can set up a call, you have been very helpful and my knowledge of both devices are greatly improved.
  • OK I've sent you an invite.

    Regards,
    Hao
  • Hi Rajan,

    The 1.6V max for VIH is an error. It should be 1.6V min and VCC max. We'll fix that soon.

    Regards,
    Hao