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Low VCO / PLL problem - Solved! Moderator can delete
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Low VCO / PLL problem - Solved! Moderator can delete

by Buggy222 on Tue Jul 07, 2009 2:22 am

I am struggling with a problem and hope perhaps that someone has solved this. I searched the forum and did not come across it.

I am at the PLL test stage. My High VCO works fine (that is to say I can see the PLL output switch from 0 to 2.2 volts at the 2GHz freqency). It will also tune.

My low VCO never seemed to switch up to 2.2 volts, until I discovered that it would in fact tune but only in the 600-650 range. On the scope I see my voltage to the ROS1700 fall to 500mv, whereas the spec sheet indicates a minimum voltage of 1.0v. As the ROS1700 transitions through 1.0v it seems to cause some kind of reset on the PLL.

Is there a simple way to stop the V-Tune falling below 1.0v? I am struggling through the program to see if I can do it there through OCR1B.

I also noticed that my buffer signal is not the 2.5VDC +1.7pp shown on the circuit diagram. I am more like 1.25VDC and 1.2pp and I wonder if this is because I used the parts list sawtooth generator instead of the one shown on the circuit diagram.

Any help would be appreciated.
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I figured as soon as I posted I would figure out my own problem. I used LMX2430 because Digikey suggested it as a replacement. They are showing the LMX2433 as obsolete.

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Buggy222
 
Posts: 7
Joined: Wed Jun 10, 2009 6:56 pm

Please be positive and constructive with your questions and comments.