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Original question:

lmx2594: LMX2594 SPUR Performance

LMX2594: 100MHz spurs when generating frequency

Louis McCotter
Prodigy 30 points

Part Number: LMX2594

Hi,

I am trying to generate a dual output LO at 5.36GHz using the LMX2594. I seem to be getting lots of 100MHz spurs away from the LO as well as the VCO output as shown in the attached photo. I have powered both outputs and have connected a 100MHz reference signal. As this is outside of the VCO core, I have selected VCO3 and enabled the channel divider (generating 10.72 GHz and then dividing by 2 to get 5.36GHz)

I believe this is likely a code issue; however, I have attempted to debug my code and cannot see any issues. Has any ever experienced this before or know any likely registers which could be causing this issue.

Thanks,

Louis

  • 0
    TI__Genius 12690 points

    Hi Louis,

    The spurs looks to high and they should not suppose to be present. As image shows, these are 114MHz away (not 100MHz), may be with higher span, it shows with error. Please check with lower span.

    I would like to see the register settings, which you are using for programming. Would be great, if you have register setting in TICS pro input format (if you already generating from TICS pro). Oscin frequency? PFD frequency?

    Regards,

    Ajeet Pal

  • 0 in reply to Ajeet Pal
    Prodigy 30 points

    Hi Ajeet, 

    I have attached the registers exported from TCIS pro below. Both Oscin and PFD frequency are 100MHz.'

    Thanks, 

    Louis

    Fullscreen LMX2594 5.36GHz Registers.txt Download 
    R112	0x700000
R111	0x6F0000
R110	0x6E0000
R109	0x6D0000
R108	0x6C0000
R107	0x6B0000
R106	0x6A0000
R105	0x690021
R104	0x680000
R103	0x670000
R102	0x660000
R101	0x650011
R100	0x640000
R99	0x630000
R98	0x620000
R97	0x610888
R96	0x600000
R95	0x5F0000
R94	0x5E0000
R93	0x5D0000
R92	0x5C0000
R91	0x5B0000
R90	0x5A0000
R89	0x590000
R88	0x580000
R87	0x570000
R86	0x560000
R85	0x550000
R84	0x540000
R83	0x530000
R82	0x520000
R81	0x510000
R80	0x500000
R79	0x4F0000
R78	0x4E0001
R77	0x4D0000
R76	0x4C000C
R75	0x4B0800
R74	0x4A0000
R73	0x49003F
R72	0x480001
R71	0x470081
R70	0x46C350
R69	0x450000
R68	0x4403E8
R67	0x430000
R66	0x4201F4
R65	0x410000
R64	0x401388
R63	0x3F0000
R62	0x3E0322
R61	0x3D00A8
R60	0x3C0000
R59	0x3B0001
R58	0x3A9001
R57	0x390020
R56	0x380000
R55	0x370000
R54	0x360000
R53	0x350000
R52	0x340820
R51	0x330080
R50	0x320000
R49	0x314180
R48	0x300300
R47	0x2F0300
R46	0x2E07FC
R45	0x2DC0F2
R44	0x2C3223
R43	0x2B0001
R42	0x2A0000
R41	0x290000
R40	0x280000
R39	0x270005
R38	0x260000
R37	0x250404
R36	0x24006B
R35	0x230004
R34	0x220000
R33	0x211E21
R32	0x200393
R31	0x1F03EC
R30	0x1E318C
R29	0x1D318C
R28	0x1C0488
R27	0x1B0002
R26	0x1A0DB0
R25	0x190C2B
R24	0x18071A
R23	0x17007C
R22	0x160001
R21	0x150401
R20	0x14D848
R19	0x1327B7
R18	0x120064
R17	0x1100FA
R16	0x100080
R15	0x0F064F
R14	0x0E1E70
R13	0x0D4000
R12	0x0C5001
R11	0x0B0018
R10	0x0A10D8
R9	0x090604
R8	0x082000
R7	0x0700B2
R6	0x06C802
R5	0x0500C8
R4	0x040A43
R3	0x030642
R2	0x020500
R1	0x010808
R0	0x00261C

  • 0 in reply to Louis McCotter
    TI__Genius 12690 points

    Hi Louis,

    Please allow some time, I'll have a look on these settings and will get back to you.

    Regards,
    Ajeet Pal

  • 0 in reply to Louis McCotter
    TI__Genius 12690 points

    Hi Louis,

    Your config file seems to be good, except output buffer value is random (50) and N fractional value is too low, but this still not induced any high amplitude spurs. Below is the captured plot on LMX2594EVM with your setting and it seems pretty clean compare to your data.

    Below is the updated config file for same frequency and modified with optimum buffer values; and measured results is very clean.

    R112	0x700000
R111	0x6F0000
R110	0x6E0000
R109	0x6D0000
R108	0x6C0000
R107	0x6B0000
R106	0x6A0000
R105	0x690021
R104	0x680000
R103	0x670000
R102	0x660000
R101	0x650011
R100	0x640000
R99	0x630000
R98	0x620000
R97	0x610888
R96	0x600000
R95	0x5F0000
R94	0x5E0000
R93	0x5D0000
R92	0x5C0000
R91	0x5B0000
R90	0x5A0000
R89	0x590000
R88	0x580000
R87	0x570000
R86	0x560000
R85	0x550000
R84	0x540000
R83	0x530000
R82	0x520000
R81	0x510000
R80	0x500000
R79	0x4F0000
R78	0x4E0003
R77	0x4D0000
R76	0x4C000C
R75	0x4B0800
R74	0x4A0000
R73	0x49003F
R72	0x480001
R71	0x470081
R70	0x46C350
R69	0x450000
R68	0x4403E8
R67	0x430000
R66	0x4201F4
R65	0x410000
R64	0x401388
R63	0x3F0000
R62	0x3E0322
R61	0x3D00A8
R60	0x3C0000
R59	0x3B0001
R58	0x3A9001
R57	0x390020
R56	0x380000
R55	0x370000
R54	0x360000
R53	0x350000
R52	0x340820
R51	0x330080
R50	0x320000
R49	0x314180
R48	0x300300
R47	0x2F0300
R46	0x2E07FC
R45	0x2DC0DF
R44	0x2C1FA3
R43	0x2B00C8
R42	0x2A0000
R41	0x290000
R40	0x280000
R39	0x2703E8
R38	0x260000
R37	0x250404
R36	0x24006B
R35	0x230004
R34	0x220000
R33	0x211E21
R32	0x200393
R31	0x1F43EC
R30	0x1E318C
R29	0x1D318C
R28	0x1C0488
R27	0x1B0002
R26	0x1A0DB0
R25	0x190C2B
R24	0x18071A
R23	0x17007C
R22	0x160001
R21	0x150401
R20	0x14E048
R19	0x1327B7
R18	0x120064
R17	0x11012C
R16	0x100080
R15	0x0F064F
R14	0x0E1E70
R13	0x0D4000
R12	0x0C5001
R11	0x0B0018
R10	0x0A10D8
R9	0x090604
R8	0x082000
R7	0x0740B2
R6	0x06C802
R5	0x0500C8
R4	0x040A43
R3	0x030642
R2	0x020500
R1	0x010808
R0	0x00251C

    In your setup, it seems to be coupling with some other sources. Have a look at any same frequency on your board, that might be coupling.

    Regards,

    Ajeet Pal