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LMX2571: Spur Generation

James Kiernan1
Prodigy 80 points
Part Number: LMX2571

We are using the LMX2571 with a 26MHz TCXO, clipped sine wave output.

At Channel 0, 1042.605Mhz we have substantial spur content. At Channel 16, 1046.702 we have very low spur content.

Please see attached for a picture of both signals along with the register settings we use for both signals.

I think the spurs we are seeing on Channel 0 are fractional spurs. If this is correct, then all I should have to do to reduce the spurs is to optimize dithering and the MULT multiplier.

Is this correct? ThanksLMX2571 Spurs.pdf LMX2571 Spurs.pdf

  • 0
    TI__Mastermind 18070 points
    Hi James,

    Channel 16 doesn't look right either. It seems that there's spur energy hidden below the skirt. I would reduce the resolution bandwidth to see if there's anything there.

    Have you tried evaluating the device with TI EVM as well as Ticspro GUI? It'll be easier for us to replicate your problem if we use the same board and GUI.

    Regards,
    Hao
  • 0 in reply to Hao Z
    Prodigy 80 points
    Hi Hao,

    In fact I looked closer in after I sent the post and saw spurs on Ch16 at 15.5kHz separation.
    I don't have a TI EVM for the LMX2571. It is mounted on my radio so it would be difficult to use the Ticspro GUI.
    Do the spurs on CH0 look like fractional spurs?

    Thanks
    James
  • 0 in reply to James Kiernan1
    TI__Mastermind 18070 points

    Hi James,

    No it doesn't look like fractional spurs. It seems to me that something went off completely.

    Can you generate your register settings in this format so that I can visualize all the settings? 

    Fullscreen 8547.HexRegisterValues.txt Download 
    R60	0x3CA000
R58	0x3A8C00
R53	0x357806
R47	0x2F6000
R46	0x2E001A
R42	0x2A0210
R41	0x290810
R40	0x28101C
R39	0x2711FB
R35	0x230C83
R34	0x221000
R33	0x210000
R32	0x200000
R31	0x1F0000
R30	0x1E0000
R29	0x1D0000
R28	0x1C0000
R27	0x1B0000
R26	0x1A0000
R25	0x190000
R24	0x18000E
R23	0x170E84
R22	0x168584
R21	0x150101
R20	0x14301B
R19	0x1303E8
R18	0x120000
R17	0x110000
R16	0x100000
R15	0x0F0000
R14	0x0E0000
R13	0x0D0000
R12	0x0C0000
R11	0x0B0000
R10	0x0A0000
R9	0x090000
R8	0x08000E
R7	0x070E44
R6	0x068884
R5	0x050101
R4	0x042020
R3	0x031200
R2	0x02E400
R1	0x017A57
R0	0x000083

    Regards,

    Hao

  • 0 in reply to Hao Z
    Prodigy 80 points

    Hi Hao,

    I have put two documents, one .txt the other .xlsx for your convenience. Thank you.

    James

    LMX 2571 Register Settings 16 bit Registers Channel 0 and Channel 16
    Ch0 Ch16
    R60 0xA000 R60 0xA000
    R58 0x8C00 R58 0x8C00
    R53 0x7806 R53 0x7806
    R47 0x0000 R47 0x0000
    R42 0x0210 R42 0x0210
    R41 0x0810 R41 0x0810
    R40 0x101C R40 0x101C
    R39 0x11F1 R39 0x11F1
    R35 0x0640 R35 0x0640
    R34 0x1000 R34 0x1000
    R33 0x0000 R33 0x0000
    R32 0x0000 R32 0x0000
    R31 0x0000 R31 0x0000
    R30 0x0000 R30 0x0000
    R29 0x0000 R29 0x0000
    R28 0x0000 R28 0x0000
    R27 0x0000 R27 0x0000
    R26 0x0000 R26 0x0000
    R25 0x0000 R25 0x0000
    R24 0x0010 R24 0x0010
    R23 0x10A4 R23 0x10A4
    R22 0x8584 R22 0x8584
    R21 0x0101 R21 0x0101
    R20 0x0028 R20 0x0028
    R19 0x0000 R19 0x0000
    R18 0x0000 R18 0x0000
    R17 0x0000 R17 0x0000
    R16 0x0000 R16 0x0000
    R15 0x0000 R15 0x0000
    R14 0x0000 R14 0x0000
    R13 0x0000 R13 0x0000
    R13 0x0000 R13 0x0000
    R12 0x0000 R12 0x0000
    R11 0x0000 R11 0x0000
    R10 0x0000 R10 0x0000
    R9 0x0000 R9 0x0000
    R8 0x000A R8 0x000A
    R7 0x1084 R7 0x1084
    R6  0x8184 R6  0x8184
    R5 0x0101 R5 0x0101
    R4 0x1019 R4 0x1019
    R3 0x0000 R3 0x0000
    R2 0x07E0 R2 0x4AA4
    R1 0x0010 R1 0x0029
    R0 0x0003 R0 0x0003
    LMX 2571 Register Settings 16 bit Registers Channel 0 and Channel 16
    Ch0 Ch16
    R60 0xA000 R60 0xA000
    R58 0x8C00 R58 0x8C00
    R53 0x7806 R53 0x7806
    R47 0x0000 R47 0x0000
    R42 0x0210 R42 0x0210
    R41 0x0810 R41 0x0810
    R40 0x101C R40 0x101C
    R39 0x11F1 R39 0x11F1
    R35 0x0640 R35 0x0640
    R34 0x1000 R34 0x1000
    R33 0x0000 R33 0x0000
    R32 0x0000 R32 0x0000
    R31 0x0000 R31 0x0000
    R30 0x0000 R30 0x0000
    R29 0x0000 R29 0x0000
    R28 0x0000 R28 0x0000
    R27 0x0000 R27 0x0000
    R26 0x0000 R26 0x0000
    R25 0x0000 R25 0x0000
    R24 0x0010 R24 0x0010
    R23 0x10A4 R23 0x10A4
    R22 0x8584 R22 0x8584
    R21 0x0101 R21 0x0101
    R20 0x0028 R20 0x0028
    R19 0x0000 R19 0x0000
    R18 0x0000 R18 0x0000
    R17 0x0000 R17 0x0000
    R16 0x0000 R16 0x0000
    R15 0x0000 R15 0x0000
    R14 0x0000 R14 0x0000
    R13 0x0000 R13 0x0000
    R13 0x0000 R13 0x0000
    R12 0x0000 R12 0x0000
    R11 0x0000 R11 0x0000
    R10 0x0000 R10 0x0000
    R9 0x0000 R9 0x0000
    R8 0x000A R8 0x000A
    R7 0x1084 R7 0x1084
    R6 0x8184 R6 0x8184
    R5 0x0101 R5 0x0101
    R4 0x1019 R4 0x1019
    R3 0x0000 R3 0x0000
    R2 0x07E0 R2 0x4AA4
    R1 0x0010 R1 0x0029
    R0 0x0003 R0 0x0003LMX2571 Register Settings.xlsx
    Fullscreen LMX2571 Register Settings.txt Download 
    LMX 2571 Register Settings			16 bit Registers		Channel 0 and Channel 16
					
					
	Ch0			Ch16	
R60	0xA000		R60	0xA000	
R58	0x8C00		R58	0x8C00	
R53	0x7806		R53	0x7806	
R47	0x0000		R47	0x0000	
R42	0x0210		R42	0x0210	
R41	0x0810		R41	0x0810	
R40	0x101C		R40	0x101C	
R39	0x11F1		R39	0x11F1	
R35	0x0640		R35	0x0640	
R34	0x1000		R34	0x1000	
R33	0x0000		R33	0x0000	
R32	0x0000		R32	0x0000	
R31	0x0000		R31	0x0000	
R30	0x0000		R30	0x0000	
R29	0x0000		R29	0x0000	
R28	0x0000		R28	0x0000	
R27	0x0000		R27	0x0000	
R26	0x0000		R26	0x0000	
R25	0x0000		R25	0x0000	
R24	0x0010		R24	0x0010	
R23	0x10A4		R23	0x10A4	
R22	0x8584		R22	0x8584	
R21	0x0101		R21	0x0101	
R20	0x0028		R20	0x0028	
R19	0x0000		R19	0x0000	
R18	0x0000		R18	0x0000	
R17	0x0000		R17	0x0000	
R16	0x0000		R16	0x0000	
R15	0x0000		R15	0x0000	
R14	0x0000		R14	0x0000	
R13	0x0000		R13	0x0000	
R13	0x0000		R13	0x0000	
R12	0x0000		R12	0x0000	
R11	0x0000		R11	0x0000	
R10	0x0000		R10	0x0000	
R9	0x0000		R9	0x0000	
R8	0x000A		R8	0x000A	
R7	0x1084		R7	0x1084	
R6 	0x8184		R6 	0x8184	
R5	0x0101		R5	0x0101	
R4	0x1019		R4	0x1019	
R3	0x0000		R3	0x0000	
R2	0x07E0		R2	0x4AA4	
R1	0x0010		R1	0x0029	
R0	0x0003		R0	0x0003

  • 0 in reply to James Kiernan1
    TI__Mastermind 18070 points
    Hi James,

    Problem replicated. Please set the MASH_ORDER to 3rd order instead of 1st order.

    Regards,
    Hao
  • 0 in reply to Hao Z
    Prodigy 80 points

    Hi Hao,

    I think you mean FRAC_Order, Register 4, change from 0x1019 to 0x4019?

    Will do this and report back presently. Thanks

    James

  • 0 in reply to James Kiernan1
    Prodigy 80 points
    Thank you very much Hao. Have a good weekend.

    James