• State TI Thinks Resolved
  • Locked Locked
  • Replies 11 replies
  • Answers 4 answers
  • Subscribers 25 subscribers
  • Views 1979 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LMK04828: Input Clock Switch/Mux & Differential to Single Ended Output

KLN
Intellectual 320 points

Part Number: LMK04828
Other Parts Discussed in Thread: LMK00304, LMK1D1204, TIDA-01023

Hi Team,

We are using LMK04828 in one of the project.

Q1: We have two input clock -100MHz to clkin  (one will be optional),

1. From external

2. On board VCXO, 

We are planning to use switch to select between the two clock as input to LMK. Could you please suggest us the switch part that can be used to select between the clock or these RF Switch part like this Mini circuit / Skyworks can be used?

Q2: We have master and slave LMK Configuration.

Master LMK Output clock will be given to Slave LMK clock input.

We will be using Slave LMK clock input in single ended, Since we are using LMK04828, Differential Output(LVPECL), we want to convert it to single ended so that can be given to Slave LMK.

Please suggest us how we can convert differential output of LMK to Single ended CLKIN signal for the slave.

Thanks.

  • 0
    TI__Mastermind 20900 points

    Hi,

    Q1, LMK04828 has two inputs (CLKin0 and CLKin1) that can be used. You can use an automatic or manual select of the input source within the device. No need for an extra external MUX.

    Q2. why do you want to have the secondary LMK to be configured to LVCMOS input? Why not using the differential input?

    Regards,

    Julian

  • 0 in reply to Julian Hagedorn
    Intellectual 320 points

    Hi 

    Julian Hagedorn said:
    Q1, LMK04828 has two inputs (CLKin0 and CLKin1) that can be used. You can use an automatic or manual select of the input source within the device. No need for an extra external MUX.

    LMK will only be used in DISTRIBUTION MODE. CLKIN1 will receive input. So, in order to switch between the two inputs, we must use a switch.

    Please suggest.

    Julian Hagedorn said:
    Q2. why do you want to have the secondary LMK to be configured to LVCMOS input? Why not using the differential input?

    Because the connection from Primary Output to Secondary LMK Input will be via matched cables, using differential input will increase the number of cables.

    So we'd like to connect a single-ended input to a secondary LMK input.

  • 0 in reply to KLN
    TI__Mastermind 20900 points

    Hi,

    ok, in distribution mode you need an external switch. Are your input clocks single ended or differential?

    You can for example use LVPECL output format and terminate the P/N pins accordingly but only route one to the secondary LMK. The Secondary LMK input can be configured like this:

    Regards,

    Julian

  • 0 in reply to Julian Hagedorn
    Intellectual 320 points

    Hi 

    Julian Hagedorn said:
    Are your input clocks single ended or differential?

    Yes, LMK in distribution mode and we need an external clock switch.

    RF Switch part like this Mini circuit / Skyworks can be used?

    Input clock shall be Single Ended. 

    Julian Hagedorn said:
    LVPECL output format and terminate the P/N pins accordingly

    Okay,

    Could you please explain it more here, with an example?

  • 0 in reply to KLN
    TI__Mastermind 20900 points

    Hi,

    termination between primary and secondary should look like this:

    Secondary input configured to Bipolar.

    We have good dual input buffers in out portfolio: LMK1D1204, LMK00304. You can consider those as muxes.

    regards,

    Julian

  • 0 in reply to Julian Hagedorn
    Intellectual 320 points

    Hi 

    We will be giving LVPECL Single ended Input to Secondary LMK from Primary LMK.

    Can you share the termination scheme for Differential to Single ended LVPECL?

  • 0 in reply to KLN
    TI__Mastermind 20900 points

    Hi.

    I attach it again:

    regards,

    Julian

  • 0 in reply to Julian Hagedorn
    Intellectual 320 points

    Hi ,

    Thanks for your reply.

    The above image shows a termination of 120 Ohm. But the datasheet recommends termination of 240 Ohm followed by AC Caps for LVPECL. 

    Is there a no need of AC Caps near the driver also?

    For the Clock Switching MUX,  Any 2:1 CLK switch suggestions? Can't these RF Switch be used?

  • 0 in reply to KLN
    TI__Mastermind 20900 points

    You can also use 240Ohms. The datasheet allows 120 to 240 ohm as emitter resistors for LVPECL.

    Caps are not needed in this case.

    For the MUX you are free to choose. I'd recommend LMK1D1204.

    regards,

    Julian

  • 0 in reply to Julian Hagedorn
    Intellectual 880 points

    Hi Julian,

    In continuation to Lakshminarayana N discussion, please clarify below points

    We want to carry out multi-channel clock sync as per TIDA-01023

    1. Could you please let us know why single ended DCLK as REF signal from Master card is being again converted to differential using Balun on the Slave card?
      1. Cant we take the single ended signal to slave card as suggested above by you? 
    2. Also can we take only single ended SDCLK as sync signal and give to Slave card?
      1. Because we have restriction on no. of RF SMA connectors in Master card

  • 0 in reply to Shekhar Kulkarni
    TI__Genius 12690 points

    Hi Shekhar,

    Shekhar Kulkarni said:
    Could you please let us know why single ended DCLK as REF signal from Master card is being again converted to differential using Balun on the Slave card?
    1. Cant we take the single ended signal to slave card as suggested above by you? 

    The above block diagram is from reference design (TIDA-01021, TIDA-01023), which has balun on board at CLKin1 input. But as Julian mentioned, you can use it as single ended input at CLKin1 with the appropriate termination (single ended input can be anything CLKin1 or CLKin1*).

    Shekhar Kulkarni said:
    Also can we take only single ended SDCLK as sync signal and give to Slave card?
    1. Because we have restriction on no. of RF SMA connectors in Master card

    CLKin0 as sync input required the DC coupled differential input. If there is a restriction for differential input, I would suggest to try with CMOS output from primary LMK and keep CLKIN0_tpye to MOS in secondary LMK in DC coupled mode.

    Thanks!

    Regards,

    Ajeet Pal