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LMX2594: HD components in the LMX2594 output clocks

Raghavendra P S
Prodigy 10 points
Part Number: LMX2594

Tool/software:

Hi TI,

 I am using clock 104 module on the rfsocZCU208 board.

  • Configured the lmx2594 for 1966.08 MHz
  • Ref clock for lmx is from lmk04828b and frequency is 245.76MHz.
  • Frequency of PFD is 245.76MHz.
  • N divider value is 48.
  • Osc2x  is disabled and pll_R and pll_Rpre divider values are 1.
  • Vco frequency is 11796.48MHz.
  • Channel divider enabled for both rf out A and out B.
  • Measurement of clock frequency from out B port(SMMP to SMA converter used) on Keysiggt MXA signal analyser.
  • Verified the R25 value for 0x0c2B.
  • Reduced the CP current at R14 register

Any suggestions what went wrong in this case??

Thanks

Raagu

  • 0
    Prodigy 10 points

    Here is the register configuration used

    R0      0x002597
R0      0x002596 
R0      0x002594
R112	0x700000
R111    0x6F0000
R110    0x6E0000
R109    0x6D0000
R108    0x6C0000
R107    0x6B0000
R106    0x6A0000
R105    0x690021
R104    0x680000
R103    0x670000
R102    0x663F80
R101    0x650011
R100    0x640000
R99     0x630000
R98     0x620200
R97     0x610888
R96     0x600000
R95     0x5F0000
R94     0x5E0000
R93     0x5D0000
R92     0x5C0000
R91     0x5B0000
R90     0x5A0000
R89     0x590000
R88     0x580000
R87     0x570000
R86     0x56FFFF
R85     0x55D2FF
R84     0x540001
R83     0x530000
R82     0x521E00
R81     0x510000
R80     0x506666
R79     0x4F0026
R78     0x4E0003
R77     0x4D0000
R76     0x4C000C
R75     0x4B0880 
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     0x2DC0C7
R44     0x2C0700
R43     0x2B0000
R42     0x2A0000
R41     0x290000
R40     0x280000
R39     0x2703E8
R38     0x260000
R37     0x250104
R36	    0x240030
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	    0x14F848
R19	    0x1327B7
R18	    0x120064
R17	    0x11012C
R16	    0x100080
R15	    0x0F064F
R14	    0x0E1E40
R13	    0x0D4000
R12	    0x0C5001
R11	    0x0B0018
R10	    0x0A10D8
R9	    0x090604
R8	    0x080000
R7	    0x0700B2
R6	    0x06C802
R5	    0x0500C8
R4	    0x040C43
R3	    0x030642
R2	    0x020500
R1	    0x010809
R0	    0x00259C
  • 0 in reply to Raghavendra P S
    TI__Guru** 107320 points

    Hi Raghavendra,

    Output is divided down from VCO, output signal is square wave, it is normal that there are harmonics. 

  • 0 in reply to Noel Fung
    Prodigy 10 points

    Isn't square waveform should only have odd harmonics??

    In the shared snapshot HD2 Component has almost same power as fundamental. 

    Are these harmonics effect the SNR of adc??

  • 0 in reply to Raghavendra P S
    TI__Guru** 107320 points

    Hi Raghavendra,

    both even and odd harmonics exist but odd harmonics are usually higher than even harmonics. 

    Your output power setting is 7, could you make it to 30? 

    I don't know the harmonics required from ADC, you'd better check with the ADC team.

    As far as I know, slew rate of this clock should affect ADC performance, so that means harmonics are needed. 

  • 0 in reply to Noel Fung
    Prodigy 10 points

    Hi Noel Fung,

    Thanks for confirmation of even and odd HD components.

    In this case even harmonic (HD2)has more power compared to odd harmonic components.

    Changed the registers R44 and R45 .

    R44(0x2c): 0x0f23 to 0x3E23.

    R45(0x2D):0xc0c7 to 0xc0fe.

    After changing these registers output power 

    Increased.

  • +1 in reply to Raghavendra P S
    TI__Guru** 107320 points

    Hi Raghavendra,

    FYI, below is the eval board performance.