power on to the frequency hangs +/- 250kHz. I don't know achieved always accurate frequency when power on?
I'm confused by your register settings. Do you really want a PFD frequency of ~14 kHz? A PFD frequency this low is going to result in very high in-band phase noise. You can probably set the R Counter value to 1 and still achieve your required performance.
Thank you, the value is wrong. I'll set PFD ~1,5MHz
Did this fix the problem?
No, no, the situation is repeated for the different settings. It could be loop filter?
It could be. What PFD frequency is your loop filter designed for? You can use our free software, ADIsimPLL, to design your loop filter.
I recommend you use a PFD frequency of 28.6 MHz, unless you have a specific reason not to. To do this, disable the REF/2 and set R counter to 1.
I'm also confused by your Band Select Clock Frequency of 70 Hz. Try increasing this to closer to 500 kHz by changing the Band Select Clock Divider value.
Thank you very much. I'll change settings registers.
Change loop filter = now to the frequency steadily reduced by 6MHz??
Please provide your new register settings and loop filter components or ADIsimPLL file.
Used loop filter of evaluation board ug - 4535.
Your Band Select Clock Frequency is still too high. It should be less than 500 kHz.
How are you measuring the output frequency?
Are you using a reference signal from an external source? Have you disconnected the on-board reference crystal (remove R59)?
Do not use Evalution board. I have only loop filter.
I'm measuring the output frequency Spectral analyzer
External RFin using LTC6905 set to 28,6MHz.
OK Band Select Clock Frequency reduce.
Something is wrong and the frequency is not fixed, but continuously reduced.
Is your REFin signal exactly 28.6 MHz? If not, your output signal will be off by the reference difference (from 28.6 MHz) * N.
Can you provide a schematic for your system?
I'm sorry, I was on holiday.
The problem is, that set the frequency is slowly reduced after the switch. I'm almost sure, that the problem is loop filter.
I'm sending schematic.
I don't know what I have to do
Please clarify "the frequency is slowly reduced after the switch".
Why are you using the fast lock loop filter? What are your lock-time requirements?
Please try this:
PIN SW disconnected and RF in 28,6MHz fix.
If your reference frequency, connected to REFin pin, is 28.6 MHz; R counter = 1 and MUXOUT is set to R_Counter_Output, then the signal on the MUXOUT pin should be 28.6 MHz. From your screenshot, it looks to be at 205 MHz. And it looks unstable/very noisy.
Can you post a plot of your LTC6905 output connected directly to the spectrum analyzer? The spectrum analyzer should be centered at 28.6 MHz.
The spectrum analyzer is centered at 28.6 MHz.
I changed the value of the components in the loop filter and the problem disappeared. The frequency is fixed.
The frequency is not exactly, but he's jumping after about 3mhz
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