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Original question:

LMX8410L: Bandwidth of the capacitors

LMX8410L: LMX8410L LO port output power and matching

Deli Geng
Prodigy 30 points
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

Fullscreen HexRegisterValues.txt Download
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
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
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

  • 0
    TI__Mastermind 33690 points

    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,

  • 0 in reply to Derek Payne
    TI__Guru** 107810 points

    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.