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Design >> Analog Design >> VCO CELL
https://designers-guide.org/forum/YaBB.pl?num=1210641554

Message started by jamie on May 12^th, 2008, 6:19pm

Title: VCO CELL
Post by jamie on May 12^th, 2008, 6:19pm

Is anyone can tell me the advantages of the capaciter connecting like this in the VCO cell? :-[

Title: Re: VCO CELL
Post by loose-electron on May 14^th, 2008, 3:48pm

It is in there to make the switching delay in the cell last longer and make the VCO tun at a lower frequency.

Title: Re: VCO CELL
Post by jamie on May 14^th, 2008, 5:35pm

I want to konw why it cennects between the differential output?

Title: Re: VCO CELL
Post by Berti on May 15^th, 2008, 12:07am

Smaller capacitor area, less coupling from ground into the output nodes .... ?

Title: Re: VCO CELL
Post by loose-electron on May 15^th, 2008, 11:27am

Berti wrote on May 15^th, 2008, 12:07am:

Smaller capacitor area, less coupling from ground into the output nodes .... ?

Berti is correct - Look at the equivlanet small signal circuit that is ground connected, it would be 2 capacitors from the two signal nodes to ground. Take the differential approach and the capacitor gets connected accross the signal nodes instead, and the total capacitance gets divided by two in value (insted of C1, C2 each being 1pf, the Cacross would be 0.5pf)

Add to that a differential system with no capactive load to ground noise.
Whenver possible, you want to keep systems differential.

-- Jerry

Title: Re: VCO CELL
Post by jamie on May 15^th, 2008, 4:46pm

Thank you very much. :)