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LMX2595: Maximizing the PLL output power at 15 GHz

Hilary Meeken
Prodigy 50 points

Part Number: LMX2595
Other Parts Discussed in Thread: LMX2594

We have the PLL programmed for 15GHz and need 7-10 dBM coming out of the PLL. How can we get the max output power out of the PLL?

Please see the schematic below, one of the filters has been changed.

Thanks!

 

  • 0
    TI__Guru** 117470 points

    Hi Hilary,

    to get higher output power, you should use inductor pull-up instead of 50Ω pull-up. See Figure 23 in the datasheet.

    BTW, if your application is up to 15GHz only, you can use LMX2594.

  • 0 in reply to Noel Fung
    Prodigy 50 points

    Noel,

    If you look at the schematic, we had an 18 nH inductor pull-up on the RFoutAP. Do we need an additional inductor pull-up somewhere else?

    Thanks!

    Hilary

  • 0 in reply to Hilary Meeken
    TI__Guru** 117470 points

    Hi Hilary,

    If you were talking about L5, that is not a pull-up, it is an AC-block.

    See datasheet section 8.1.4 for details of RF output buffer pull-up.

  • 0 in reply to Noel Fung
    Prodigy 50 points

    Hi Noel,

    I programmed the TI Eval board to output 15GHz and was seeing -7 dBm at RFoutA. Using our board I was see -20 something dBm.

    I attached both the eval board (100 MHz) and our board (40 MHz) register files. Perhaps I'm not programming them correctly.

    Hilary

    Fullscreen 15GHz_40MHz_clk_HexRegisterValues.txt Download 
    R112	0x7000F8
R111	0x6F0010
R110	0x6E04EC
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	0x3A8001
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	0x2DC8C0
R44	0x2C1FA3
R43	0x2B01F4
R42	0x2A0000
R41	0x290000
R40	0x280000
R39	0x2703E8
R38	0x260000
R37	0x250404
R36	0x2400BB
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	0x14C048
R19	0x1327B7
R18	0x120064
R17	0x110000
R16	0x100080
R15	0x0F064F
R14	0x0E1E70
R13	0x0D4000
R12	0x0C5001
R11	0x0B0018
R10	0x0A10D8
R9	0x091604
R8	0x082000
R7	0x0740B2
R6	0x06C802
R5	0x0500C8
R4	0x040A43
R3	0x030642
R2	0x020500
R1	0x010808
R0	0x00241C

    Fullscreen 15GHz-100MHzRef_HexRegisterValues.txt Download 
    R112	0x7000F8
R111	0x6F0010
R110	0x6E04EC
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	0x3A8001
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	0x2DC8C0
R44	0x2C1FA3
R43	0x2B0000
R42	0x2A0000
R41	0x290000
R40	0x280000
R39	0x2703E8
R38	0x260000
R37	0x250404
R36	0x240096
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	0x14C048
R19	0x1327B7
R18	0x120064
R17	0x110000
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	0x00241C

  • 0 in reply to Hilary Meeken
    TI__Guru** 117470 points

    Hi Hilary,

    R20 0x14C048 --> VCO_SEL = 0 is invalid. Suggest make it 0x14E048.
    R17 0x110000 --> VCO_DACISET_STRT = 0 is not a good choice. Suggest make it 0x11012C.

    Other suggestions:

    Read Table 34 for SEG1_EN usage.

    Make OUTB_MUX = OUTA_MUX, see datasheet section 7.3.7 for details.

  • 0 in reply to Noel Fung
    Prodigy 50 points

    noel,

    The max power we can get out of the PLL is -5 dBm at 15GHz.  We are still short by about 11 dB.  Section 8.1.4 of the datasheet suggests pull up configuration for higher power.  For a single ended 15GHz output it is recommended that an inductor or 50 Ohm thin film resistor to be used as a pull up component.  What is the best inductor value at this frequency?  If we use the resistor listed in the datasheet, do we still need an inductor as a DC block?

    Also can you comment on the filter values used in my schematics?  I used the PLLatinum Sim to come up with the values but not sure it is the best design or use the same filter on the EVM board.

    Thanks,

    Hilary

  • 0 in reply to Hilary Meeken
    TI__Guru** 117470 points

    Hi Hilary,

    For inductor pull-up, we suggest 1nH to 3nH inductors. We have tried the following inductors.

    Inductor Vendor Part# Q SRF(MHz) RDC(ohm)
    1nH Toko LL1005-FH1N0S 10 13599 0.1
    3.3nH Toko LL1005-FH3N3S 10 6800 0.19

    To use inductor pull up, simply replace R915, R919 with inductors.

    Can you send me your PLL Sim file? What are you trying to optimize? Phase noise, jitter, spurs, etc?

  • 0 in reply to Noel Fung
    Prodigy 50 points

    Noel,

    We are still not seeing an output power greater than -5dBm on our board. We have a ,single-ended output Port, Port A, configuration. I have configured the PLL using VCO2x_EN=0 AND VCO2X_EN=1 with the appropriate OUTx_PWR setting and see no difference in the output power. We have tried adding an 1-nH inductor pullup as well as a 50-ohm resister just to see if we could get any increased output power, but didn't get any additional power. In order for our board to work, we need to had the PLL programmed for 15GHz and have an output power greater than 5dBm. Is it possible to schedule a conference call?

    Thanks!

    Hilary  

  • 0 in reply to Hilary Meeken
    TI__Guru** 117470 points

    Hi Hilary,

    When you measured the output power, did you remove C1135 or R931? Did you AC-couple the signal to the test equipment?

    Can we review your pcb layout?