The Designer's Guide Community
Forum
Welcome, Guest. Please Login or Register. Please follow the Forum guidelines.
Oct 21st, 2020, 11:46am
Pages: 1
Send Topic Print
Wide tuning range VCO design problem (Read 2963 times)
gggould
Guest




Wide tuning range VCO design problem
Apr 09th, 2004, 8:41pm
 
Hi all,

I am designing a VCO with varactor and switching cap to cover 800MHz wide. But I find that the VCO gain and amplitude variations are big problems. Both Kvco and output amplitude increase with the operating frequency...

Any tips or advices?

Thank you very much...
Back to top
 
 
  IP Logged
wizz
New Member
*
Offline



Posts: 4

Re: Wide tuning range VCO design problem
Reply #1 - Apr 12th, 2004, 8:51pm
 
To minimize Kvco variation, you could use a lot of switching bands. You'll find up to 8bits worth of bands in published VCO's if I'm not mistaken (which means you need to put in 256 swiched caps). Could be it was 6 bits, which would mean 64 switched capacitors.

And 800MHz tuning: doesn't say anything about difficulty; it's the percentage that counts. If you're trying to do 50-850MHz with one LC VCO I wish you good luck Smiley. If it is around 17GHz, it shouldn't be that hard....

wizz
Back to top
 
 
View Profile   IP Logged
Fei
Junior Member
**
Offline



Posts: 16

Re: Wide tuning range VCO design problem
Reply #2 - Apr 19th, 2004, 11:46am
 
The variation is caused by the "ON" resistance of the switch transistor.  There are a few things you can do to mitigate the effect:

1). Using a larger size transistor;

2). Using an additional cap in series to the switched cap tanks.

Hope it helps

Fei

Back to top
 
 
View Profile   IP Logged
Pages: 1
Send Topic Print
Copyright 2002-2020 Designer’s Guide Consulting, Inc. Designer’s Guide® is a registered trademark of Designer’s Guide Consulting, Inc. All rights reserved. Send comments or questions to editor@designers-guide.org. Consider submitting a paper or model.