Other Parts Discussed in Thread: LMX2572,
Hi all
Would you mind if we ask LMX2572?
Could you refer to the attachment file?
0361.20200406_LMX2572EVM.pdf
20200406_LMX2572EVM.tcs
Kind regards,
Hirotaka Matsumoto
This thread has been locked.
If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.
Hi all
Would you mind if we ask LMX2572?
Could you refer to the attachment file?
0361.20200406_LMX2572EVM.pdf
20200406_LMX2572EVM.tcs
Kind regards,
Hirotaka Matsumoto
Hi Matsumoto-san,
With a correct FSK SPI FAST setting, you should get a single tone signal at Fo + delta F. For example, if Fo = 1GHz and delta F = 1MHz; you should get a single tone signal at 1.001GHz.
The problem you have is you are trying to do a delta F of 62.2MHz. This is not possible with the FSK function because the VCO will have to change its frequency by 124.4MHz. This VCO frequency change is only possible with a VCO calibration. However, FSK does not do VCO calibration. That's why you are not getting a correct output frequency.
Noel san
Thank you so much for your reply!
The problem you have is you are trying to do a delta F of 62.2MHz.
This is not possible with the FSK function because the VCO will have to change its frequency by 124.4MHz.
This VCO frequency change is only possible with a VCO calibration. However, FSK does not do VCO calibration.
That's why you are not getting a correct output frequency.
->We got that the VCO will have to change its frequency by 124.4MHz in case of FSK function.
Could you inform us the precedure with correct output frequency by 124.4MHz?
FSK doesn't do VCO calibration, so how much of VCO's frequency does it use for FSK function?
Kind regards,
Hirotaka Matsumoto
Noel san
Thank you so much for your cooperation always!
We got that the problem is that we are trying to do a delta F of 62.2MHz.
And we also understand we have to choice the lower value of FSK_SPI_FAST_DEV.
So, we would like to confirm you two points finally.
<Question1>
How much is the range which VCO can do calibraton?
We understand that 62.2MHz is bigger, so we would like to know suitable value.
<Question2>
We would like to calculation formula.
If FSK_SPI_FAST_DEV is 1, how much will be the output frequnecy?
Kind regards,
Hirotaka Matsumoto
62.2MHz
Noel san
Thank you so much for your cooperation always.
And then, we are sorry that our explanation makes confuse you.
We would like to ask you about <Question1> and <Question2>.
What we would like to confirm on <Question1> is follow;
I suspect that, in FSK mode, if the frequency shift is small, the VCO calibration may not be necessary.
If it is true, how much frequency offset can the device be operational without VCO calibration?
What we would like to confirm on <Question2> is follow;
On the dault setting, if FSK_SPI_FAST_DEV increase +1, how much will the output frequency be?
Kind regards,
Hirotaka Matsumoto
Hi Matsumoto-san,
Without calibration, the tunable range is around maybe 60M to 80MHz, I would suggest not driving it over 50MHz.
from equation 9, FSK step = Round[(delta F x PLL_DEN x CHDIV) / (fPD x 2^FSK_DEV_SCALE)]
if FSK step = 1, then delta F = 1 x fPD x 2^FSK_DEV_SCALE / PLL_DEN / CHDIV
Noel san
Thank you so much for your reply always!
We got it.
Just in case, we would like to confirm one point whether our recognition is correct or not.
On the default EVM setting;
fPDx=100MHz
2^FSK_DEV_SCALE=1
/ PLL_DEN =1000
/ CHDIV=1
delta F = 1 x fPD x 2^FSK_DEV_SCALE / PLL_DEN / CHDIV
->Δf=100kHz
In this case, this Δf is within the calibration's tunable range.
In case of 2^FSK_DEV_SCALE=662;
delta F = 1 x fPD x 2^FSK_DEV_SCALE / PLL_DEN / CHDIV
->Δf=66.2MHz
In this case, this Δf may be within of the calibration's tunable range. However, this value is no recommended tunable range.
Kind regards,
Hirotaka Matsumoto