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LMX2594EVM: lmx2594 spur issue

Part Number: LMX2594EVM
Other Parts Discussed in Thread: LMX2594, LMK04832

Hi:

again, We design the new board and have another spur, shown below, which we found about 200Hz away from our Lo, and set register. 

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 0x2C1F23
R43 0x2B0F00
R42 0x2A0000
R41 0x290000
R40 0x280000
R39 0x273000
R38 0x260000
R37 0x250404
R36 0x2400C3
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 0x14E048
R19 0x1327B7
R18 0x120064
R17 0x11012C
R16 0x100080
R15 0x0F064F
R14 0x0E1E30
R13 0x0D4000
R12 0x0C5002
R11 0x0B0018
R10 0x0A10D8
R9 0x090604
R8 0x082000
R7 0x0740B2
R6 0x06C802
R5 0x0500C8
R4 0x040C43
R3 0x030642
R2 0x020500
R1 0x010808
R0 0x002418

  • Hi Jane,

    What clock source did you use?

    If you were using a 100MHz reference clock and the output is 6GHz, there should be no spurs except fpd spurs (appears at phase detector frequency). 

    Low frequency spurs are usually came from the reference clock. Synthesize at integer channel will not generate low frequency noise. 

  • Hi Noel:

    Thank you for your reminder,  We use LMK04832 to regenerate the 122.88MHz system clock for jitter cleaner reasons then plugin LMX2594 to synthesize 6GHz  for RF Lo. if we need to cut this source instead 122.88 from the signal generator to check it or  check LMK04832 setup?

    B.R. Jane

  • Hi Jane,

    frequency synthesizers, including LMK devices (PLL + VCO/VCXO), at integer channel, will not generate this kind of low frequency spurs. If we see this spurs, usually it is a power supply issue or test equipment issue. 

    if you can measure phase noise and see multiple 50Hz spurs as well, then the 200Hz is likely came from AC power supply line.