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My VCO in LTC6946-4 does not work

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JTak

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Hi everyone,

I designed and fabricated LTC6946-4 PCB board.

According to the datasheet, VCO in the chip can produce signal in the frquency range 4.2~6.4GHz.

However, my PLL can generate only 4.4~5GHz when the voltage at TUNE pin is 0~5V.

Informations of my pll is here.
F_ref = 26MHz.
N = 1000
R = 5
O = 2(actually, i want the signal in 2.1~3Ghz)
Rz=930 ohm
Ci=1.54nF
Cp=0.13nF

The loop filter elements are calculated using PLLWizard from Limear technology.

Is there something I miss?
 

Hi,

I don´t have experience with the chip you use.

But in the frequency range the PCB layout will have big influence on the performance.
Please show us your schematic, your PCB layout and best if you could provide some manufacturer codes of the other parts used. Like capacitors, inductors and so on.


Klaus
 

KlausST /
Thanks for your reply.

I followed the schematic in the datasheet page 29.

When I test the device using spectrum analyzer, the device operates very well but only in 2.2~2.5 GHz range.

PCB layout is here.
layout1.png

Using this layout, I etched on FR-4 of which thickness is 0.8mm.

Unfortunately, I don't know providers of other elements.
 

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