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LMX2595: SYNC option utilization

Allamaprabhu B
Prodigy 70 points
Part Number: LMX2595

Hi,

We are using LMX2595 for RF generation in the range 15 GHz to 17.8GHz. Reference input is 100 MHz.(Exact frequencies: 15.555,16.055,17.805 GHz) 

We suspect, for each power ONs and w.r.to temperature the phase or delay between Oscin and RFout is changing.

Please suggest how to SYNC 100 MHz reference clock to RF out with fixed delay.

I want fixed phase relationship or delay from OSCin to fOUT for each power ONs and temperature change.

(Currently we are not programmed and used SYNC related options in the IC)

Thanks in Advance.

  • 0
    TI__Genius 11900 points

    Hello Allamaprabhu,

    Phase between OSCin and RFout changing is expected unless using the device in a mode that is compatible with SYNCing the device. In this case the RFout and OSCin will be phase deterministic, that is, the phase difference between the two will be constant (not 0 phase difference). This can be associated with the propagation delay through the part.

    Please refer to "Figure 33. Determining the SYNC Category" and "7.3.11 Phase Synchronization"

    "(Currently we are not programmed and used SYNC related options in the IC)"

    I am not sure I understand this statement, can you elaborate?

    Thanks,

    Vibhu

  • 0 in reply to Vibhu Vanjari
    Prodigy 70 points

    Hi Vibhu,

          We are using RFoutA port, as our required frequency is >15 GHz hence we are not using Channel divider block(it is default value = 2). With this first condition Pass(Fig33)(correct me if i am wrong)

    Currently Fpd= 200 MHz since Doubler is enabled in clock path. If Doubler changed to 1 then Fpd will be 100MHz and this corresponds to M=1, Pass(Fig33)

    But the RFout(15.555GHz) is not integer multiple of clock 100 MHz. Hence fOUT % fOSC = 0 condition fails and leads to Category 3.

    So this shows Category 2 is only for integer synthesis and not for fractional one. Is it correct?

    Does this mean i should use only Category 3, for reference clock 100 Mhz and mentioned RFout frequencies?

    If possible please share the register values or TICS pro screen shot for Fosc in = 100 MHz and Fout= 15.555 GHz with category 3 (or with category 2 if possible).

    (My goal is to have fixed phase delay between Oscin and RFout every time i program after Powering it ON and also over the its operating temperature)
     

  • 0 in reply to Allamaprabhu B
    TI__Genius 11900 points

    Hello Allamaprabhu,

    Yes your configuration would be Category 3 SYNC. Which requires an external timing critical SYNC signal.15.555GHz-SYNC-e2e.tcs

    I haven't tested this configuration, but it should be a good starting point. Few things that are important:

    1. INPIN_IGNORE = 0, so that the SYNC pin can be used
    2. Fpd must be lowered to allow a large enough N-divider as you also have a IncludedDivide in SYNC mode

    Thanks,

    Vibhu