LMX2820: LMX2820 LOOPBACK mode does not change frequency

lian ales

Part Number: LMX2820

I changed the lmx2820 from normal mode to loopback mode,in the normal mode i locked to 6GHz， and when i changed to loopback mode,the frequency is stll 6GHz.

In the loopback mode ,i use a DDS as a external fractional-N divider,and i changed the frequency to 6005.999MHz,or other frequency near 6GHz,no more than ±50MHz，but the frequency did not change,still locked to 6GHz,

the LMX2820 register, i only changed 0xh220010 to 0x220810, and the DDS's FTW ( to change fractional frequency ), is there any other register i should configure

1 个月前

0 Lydia 1 个月前

TI__Mastermind 29705 points

您好，已经收到了您的案例，调查需要些时间，感谢您的耐心等待。

0 Eirwen 1 个月前回复 Lydia

TI__Mastermind 24405 points

Do you have a block diagram?

0 lian ales 1 个月前回复 Eirwen

Prodigy 30 points

0 Eirwen 1 个月前回复 lian ales

TI__Mastermind 24405 points

Before loopback mode is enabled (0x220010), internal VCO goes to the N-divider directly. Given VCO =6000MHz, fpd = 100MHz, PLL_N = 60, PLL_NUM = 0.

Now enable loopback mode (0x220810), the frequency going to the N-divider is now 2400MHz, so PLL_N needs to change to 24.

Can you get it lock with this configuration?

0 lian ales 1 个月前回复 Eirwen

Prodigy 30 points

if i change PLL_N to 24，it will lose lock

0 Eirwen 1 个月前回复 lian ales

TI__Mastermind 24405 points

It should lock as other customers do not have this problem.

I don't know why it did not work on your side. Currently I don't have the setup to verify this application, I need to purchase some mixer and filters to setup the test environment.

I will keep this post open and get back to you once I have the setup established, probably in two weeks.

0 lian ales 1 个月前回复 Eirwen

Prodigy 30 points

ok,thanks,I am expecting to hear good news!

0 lian ales 5 天前回复 Eirwen

Prodigy 30 points

is there any result

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LMX2820: LMX2820 LOOPBACK mode does not change frequency