LMX8410L: LO output sync to the mixer

Deli Geng

Part Number: LMX8410L
Other Parts Discussed in Thread: LMX2594

I have a close circuit application of LMX8410, where the LO output is used to drive a separate upconverting I/Q mixer, whose output is looped back somehow to the LMX8410. The main LO frequency is around 6HGz, so I need to use the div2 mode of the I/Q generator.

The problem is, when the LO is effectively set to different frequencies around 6HGz, the LO output appears to have random times of 90 degree shift from the LMX8410 internal mixer LO. And in my application, I can see I/Q swap and shift accordingly. I understand that LO output can use the VCO channel divider and the div2 mode of the I/Q generator has its own divider, so there can be such misalignment.

From the datasheet, I gathered the LO output can be synchronized to the SYNC signal and the mixer can only synchronize to SYNC when the frequency is whole times of Fosc, which is not always the case in my application. However, I realize the the R80 register seems to address the mixer LO sync issue, especially the control bit of SYNC_PHASE_MIXLO Sync bit to close the loop from Mixer LO back to synthesizer looks promising.

Is it possible to sync the LO output to the mixer under div2 mode, for example at 6.000001GHz when the Fosc is 0.1GHz? and any chance to know more details about how to use the SYNC_PHASE_MIXLO control bit?

Many thanks,

David

over 2 years ago

0 Ajeet Pal over 2 years ago

TI__Genius 12560 points

Hi David,

From the LMX8410L datasheet, LO_OUT can be synchronized with OSCin same as LMX2594. With your operating frequency (LO - 6.000001GHz and Fosc - 0.1GHz), this becomes in category - 3 and would need an external SYNC, which is time critical.

Whereas SYNC of I/Q output to OSCin is not possible for your operating, where it would need an VCO frequency is multiple of Fosc, which is not true in your applications.

For 6G LO frequency and 100M OSCin frequency, it could be possible.

Thanks!

Regards,

Ajeet Pal

0 Deli Geng over 2 years ago in reply to Ajeet Pal

Prodigy 30 points

Hi, Ajeet,

Thanks for your reply. Any chance to know more details about the SYNC_PHASE_MIXLO control bit? in case of it can help under certain conditions.

Regards,

David

0 Ajeet Pal over 2 years ago in reply to Deli Geng

TI__Genius 12560 points

Hi Deli,

SYNC_PHASE_MIXLO control bit enables the mixer LO back to synthesizer, which can be "I" LOGEN /2 or LOGEN Polyphase and include the mixer in PLL loop.

Here, LO output can also be from mixer "Q" LO, which would be 90deg phase shift from the mixer "I" LO.

Thanks!

Regards,

Ajeet Pal

0 Deli Geng over 2 years ago in reply to Ajeet Pal

Prodigy 30 points

Hi, Ajeet,

Thanks again for your reply. The diagram looks very promising for what I need. Although I can't find the exact LO OUT SEL bits from the datasheet, I believe it is the LO_OUT_MUX which is in the R46 register. However, when you look at page 43 for the R46 register, i.e. LO_OUT_MUX, it does not give the settings for the mixer Q LO. I know there are only two combinations, so I can probably try-and-error myself. It would still be nice to know the right way.

Regards,

David

PS. did I miss the application note for this device if there is any? or a piece of reference source code?

0 Ajeet Pal over 2 years ago in reply to Deli Geng

TI__Genius 12560 points

Hi David,

LO_OUT_MUX are the correct bits for the Mixer LO output select, but it is hidden and not mentioned in the datasheet.

0x2 value for the LO_OUT_MUX will bring the mixer port LO.

Please try with this settings.

Thanks!

Regards,

Ajeet Pal

0 Deli Geng over 2 years ago in reply to Ajeet Pal

Prodigy 30 points

Hi, Ajeet,

Thanks again for your help. However, that 0x2 value for LO_OUT_MUX does not work.

For some reason, the register value exported from the TI eval tool is 0x07FC for LO output by the chain divider. So I replaced it with 0x07FE, then there was no output from the LO pin. I tried 0x0002 and 0x07FF, still no good.

I enclosed my register initial table, would you mind helping to see if I missed anything? or if you could load it to your eval board to see if you have the 6GHz LO output.

Regards,

David

/*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*/, 0x540C80
/*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 // change to support mixer LO output
/*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*/, 0x010808
/*R0*/, 0x002010

0 Deli Geng over 2 years ago in reply to Ajeet Pal

Prodigy 30 points

BTW, could you also please confirm the register values if I want to enable the red and yellow path in your last diagram. Many thanks

0 Ajeet Pal over 2 years ago in reply to Deli Geng

TI__Genius 12560 points

Hi David,

I'll check the config file in evaluation board and will get back to you.

Thanks!

Regards,
Ajeet Pal

0 Deli Geng over 2 years ago in reply to Ajeet Pal

Prodigy 30 points

Hi, Ajeet,

Thanks for looking into this for me. Have you been able to conduct the test?

Since I need an LO output in a fixed phase with the mixer LO, either of the following solution should solve my problem,

1) get LO output from the mixer;

2) put mixer LO in the PLL loop, and hopefully sync the chain divider to the mixer LO in this way.

Regards,

David

0 Ajeet Pal over 2 years ago in reply to Deli Geng

TI__Genius 12560 points

Hi David,

Were you not able to lock the PLL or not getting the LO out from mixer in the above configuration?

Thanks!

Regards,

Ajeet Pal

0 Deli Geng over 2 years ago in reply to Ajeet Pal

Prodigy 30 points

Hi, Ajeet,

I don't have details of the register setting for either of the configurations. The mixer LO output setting as you suggested didn't produce any LO output as mentioned in my previous reply.

So in order to avoid any misunderstanding, can I bother you to provide the full register settings for enabling the mixer LO output? and/or the settings for putting the mixer LO in the PLL loop.

Many thanks,

David

0 Ajeet Pal over 2 years ago in reply to Deli Geng

TI__Genius 12560 points

Hi David,

As these functions are not commonly used and hence not described in detailed.

Here, I am attaching the config file, which is updated for the Mixer LO output "Q" enable and Mixer "I" feedback to the synthesizer.

LMX8410L_MixerLO_Output.tcs

This would need to be enable (already updated in config file):

1. SYNC_PHASE_MIXLO, SYNC_DRV2_EN and SYNC_DRV1_EN bit should be "1" for enabling the Mixer path back to the synthesizer and sync the drivers from the LO output path. R80[11:9] --> 0x7

2. As feedback path is using the internal div/2, N value need to be change (/2) for locking the PLL.

3. "Q" output driver enable for LO out. R80[7:8] --> 0x3

4. LO output mux select for mixer out enable. LO_OUT_MUX, R46[1:0] --> 0x2

Thanks!

Regards,

Ajeet Pal

0 Deli Geng over 2 years ago in reply to Ajeet Pal

Prodigy 30 points

Hi, Ajeet,

Thanks again. It appears to work. I can see the LO output on the SA. I'll run it in the lab tomorrow to find out if tracks different LO frequency settings.

Also, may I ask more questions? Is there some control bits hidden in R80(0x50)? By my original setting, it was 0x0009, and when I set the R46 to 0x07FE, the LO output had noting. If I copy your register settings for this part, and make R80 to 0x0189, R46 is still 0x07FE, and there is the mixer LO signal output. These two bits changed are marked as "reserved" in the datasheet although they do play an important role. Any chance to shade more light on the function of these bits?

Regards,

David

0 Ajeet Pal over 2 years ago in reply to Deli Geng

TI__Genius 12560 points

Hi David,

That's correct. R80[8:7] bits mentioned as reserved/hidden and the default value "0" disabled the "Q" output driver/buffer for LO out. If wants to enable LO out from mixer Q, these bits needs to be changed to "1", which is showed in previous reply.

Similarly for the LO_OUT_MUX settings are not disclosed in the datasheet for Mixer LO out and that needs to set to 0x2 for the output.

Thanks!

Regards,

Ajeet Pal

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LMX8410L: LO output sync to the mixer