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LMX8410L: LMX8410L LO port output power and matching

Part Number: LMX8410L
Other Parts Discussed in Thread: , LMX2594

Hi,

I'm using the LMX8410L's LO as output. I have the LMX8410LEVM board. I put 50ohm resistors on the board as LO pull-up. According to the datasheet Fig 44, shall I expect 2dBm output power at 6GHz? However, my SA only shows about -5.9dBm at the peak. Did I missed something in this test? I also gathered using inductors as pull-up can generate more powerful output. What value would be recommended for 6GHz?

Many thanks,

David

PS. IIRC, it is said that there is an LMX2594 inside LMX8410, but I found the LO output specification quite different between these two components.  

The LMX8410 register data enclosed

HexRegisterValues.txt
R127 (INIT1)	0x7F0003
R6 (INIT2)	0x060100
R127	0x7F0000
R126	0x7E8000
R125	0x7D0000
R124	0x7C0000
R123	0x7B0000
R122	0x7A0000
R121	0x790000
R120	0x780000
R118	0x760000
R117	0x7500C0
R116	0x740000
R115	0x730F00
R114	0x720000
R113	0x710000
R112	0x700000
R111	0x6F0000
R110	0x6E0000
R109	0x6D0000
R108	0x6C0000
R107	0x6B0000
R106	0x6A0000
R103	0x672C00
R102	0x660000
R101	0x650002
R100	0x640002
R99	0x630000
R98	0x620000
R97	0x610000
R96	0x609218
R95	0x5F0000
R94	0x5E8080
R93	0x5D0000
R88	0x580003
R87	0x570000
R86	0x560000
R85	0x550000
R84	0x541900
R83	0x530020
R82	0x520A23
R81	0x510310
R80	0x500009
R79	0x4F0000
R78	0x4E0064
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	0x3E0022
R61	0x3D00A8
R60	0x3C03E8
R59	0x3B0001
R58	0x3A8001
R57	0x390000
R56	0x380000
R55	0x370000
R54	0x360000
R53	0x350000
R52	0x340820
R51	0x330080
R50	0x320000
R49	0x314180
R48	0x300300
R47	0x2F0300
R46	0x2E07FC
R44	0x2C1F22
R43	0x2B0000
R42	0x2A0000
R41	0x290000
R40	0x280000
R39	0x272710
R38	0x260000
R37	0x258204
R36	0x240078
R35	0x230004
R34	0x220000
R33	0x211E21
R32	0x200393
R31	0x1F43EC
R30	0x1E318C
R29	0x1D318C
R28	0x1C0488
R27	0x1B0002
R26	0x1A0DB0
R25	0x190624
R24	0x18071A
R23	0x17007C
R22	0x160001
R21	0x150401
R19	0x1327B7
R18	0x120064
R17	0x1100FA
R16	0x100080
R15	0x0F064F
R14	0x0E13F0
R13	0x0D4000
R12	0x0C5001
R11	0x0B0018
R10	0x0A10D8
R9	0x090604
R8	0x082000
R7	0x0700B2
R6	0x06C802
R5	0x0500C8
R4	0x041943
R3	0x030642
R2	0x020500
R1	0x01080B
R0	0x002010

  • Hello David,

    I note that Figure 44 suggests board and cable losses are not removed from the measurement. Is it possible this discrepancy is a result of cabling losses? If you have the device connected to the SA with a short cable, I find that explanation unlikely, but it's worth checking.

    The output power is sensitive to layout and soldering of the 50Ω components as well, so this may be having an effect. There is some explanation of the reasoning of the inductive pullup benefit in the LMX2594 datasheet (you heard correctly, an LMX2594 is used as the integrated synthesizer).

    E2E is going down for maintenance until 12am central time on Sunday, but when it returns I'll offer some comment on your register values.

    Regards,

  • Hi David,

    Could you readback R45? Also check if this is a silly soldering issue at the LO_M or LO_P SMA connectors. We have bad experience with this SMA connector in the past.