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Design >> RF Design >> LC VCO buffer
https://designers-guide.org/forum/YaBB.pl?num=1277823293

Message started by casual on Jun 29^th, 2010, 7:54am

Title: LC VCO buffer
Post by casual on Jun 29^th, 2010, 7:54am

Could I directly connect CML buffer to the output of LC VCO tank?
If the CML buffer is too strong, it might couple back to the VCO tank.

The alternative is to use ac couple to CML buffer. however it reduces the output amplitude and the tuning range.

What is the common practice?

Title: Re: LC VCO buffer
Post by rfcooltools.com on Jun 29^th, 2010, 11:09am

Aside from amplitude possibly being to large
Most of the time fixed capacitance reduction on the tank is the target. so ac coupling is almost always used to reduce this.

http://rfcooltools.com

Title: Re: LC VCO buffer
Post by casual on Jul 5^th, 2010, 2:23am

ac couple might introduce additional loss to the tank if the R after the ac cap is too low....

Title: Re: LC VCO buffer
Post by rfcooltools.com on Jul 6^th, 2010, 10:01pm

depends on the capacitance
If the cap is small then the resistance will be weighted accordingly.

http://rfcooltools.com

Title: Re: LC VCO buffer
Post by love_analog on Jul 29^th, 2010, 6:30am

Remember that ac coupling cap has parasitics to ground so you're amplitude will become lower before it hits your buffer.

Also the ac coupling cap will reduce your freq of oscillation which will be compensated by Cbank or vctl on VCO