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LMX2595EVM: LMX2595 EVM - Output Power is super Low

Prodigy 40 points

Replies: 6

Views: 99

Part Number: LMX2595EVM

Testing the LMX2595 EVM and the output power at 8 GHz without doubler enabled is good, around 3.62 dBm with 50 Ohm Resistor pull-up, and around 6.92 dBm with Inductor pull-up. However, when I enable the doubler to get 16 GHz the power decreases dramatically to -30.3 dBm with 50 Ohm Resistor pull-up, and around -26 dBm with Inductor pull-up. Per the datasheet P.63 Output power graph Fig-58, the Output power at 16 GHz should be around -1 dBm. Changing DBLR_IBIAS_CTRL1 does not improve output power, and twiddling the OUTA_PWR register in TICS Pro has little effect as well. The initial output inductor and capacitors were not designed for 16 GHz and the Output power results were 5 - 7 dB worse then the numbers I measured above after re-tuning the output to a 1nH inductor resonant at 16 GHz and 0.3pF capacitor resonant at 16 GHz.. I already designed this part into a product and the board is in fabrication so I'm panicking about the output power. Any suggestions to improve output power are appreciated. 

  • Hi Rob,

    Just wanted to make sure that you have set R45[12:11], OUTA_MUX to 0x2 and R27[0], VCO2X_EN=1?

  • In reply to Noel Fung:

    Hi Noel, thanks for your quick reply. The register R45 is set to 0x2DD0D4, and register R27 is set to 0x1B0002. It seems I had missed checking the VCO2X_EN and after clicking it I got an immediate power boost to around -18 dBm. Much better results but still far from the datasheet values. Can you think of anything else that would boost the power? Have you measured other LMX2595 EVM boards and checked the output power, and do they match the datasheet? FYI, I checked my cable loss and its around -1.5 dB and DC voltage set to 3.3V with current drawing 430 mA currently.

  • In reply to Rob Monroe:

    Hi Rob,

    Can I have your TICS Pro register setting?

    Is reference clock frequency = 100MHz?

  • In reply to Noel Fung:

    Hi Noel, i'm using the on-board 100 MHz VCO for the REF. The registers are below:

    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 0x2E07FD
    R45 0x2DD0D4
    R44 0x2C3FA3
    R43 0x2B0000
    R42 0x2A0000
    R41 0x290000
    R40 0x280000
    R39 0x2703E8
    R38 0x260000
    R37 0x250404
    R36 0x240050
    R35 0x230004
    R34 0x220000
    R33 0x211E21
    R32 0x200393
    R31 0x1F03EC
    R30 0x1E318C
    R29 0x1D318C
    R28 0x1C0488
    R27 0x1B0003
    R26 0x1A0DB0
    R25 0x193115
    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 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 reply to Rob Monroe:

    Hi Rob,

    Output power is not max. with OUTA_PWR=63. See datasheet Figure 26 for details. Try make this register equal to around 31. 

    R25 should be changed to 0x190C2B. (0x0C2B = 3115)

    Hopefully these changes fix your problem.

  • In reply to Noel Fung:

    Noel, those register settings are a success! I measure 5.3 dBm output power at 16 GHz. The only hardware modification I made is installing Coilcraft 0402HP-1N0X, 1nH Inductor pull-ups to 3.3V at the outputs (resonant at 16 GHz) and 3.3V bypass capacitor and output series capacitors Murata GRM1555C2AR40BA01D (Cap, 0.4 pF,100V, COG, 0402) resonant at 16 GHz. No other modifications were made aside from the register settings you suggested. The phase noise I measure is similar but slightly worse than the datasheet P.16 Fig-10. I measure -100.5 dBc/Hz @ 10 KHz, -101.8 dBc/Hz @ 100 KHz and -119.5 dBc/Hz @ 1 MHz. Thanks for your suggestions and support!