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Designing a buffer for VCO LC 2.5 Ghz

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dinesh agarwal

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my vco control voltage get imposition of the oscillation from the output

the oscilltaion are of magnitude 32mv

i am using accomulation mode varactor

the result PLL not getting locked

i am using two varactors in series

the common point say drain - source are connected to V control

thank
 

vfone

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Re: VCO LC 2.5G hz

Use a buffer amplifier after the VCO, to boost the generated signal.
 

roee_by

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Re: VCO LC 2.5G hz

I'm designing a CMOS cross-coupled VCO at 4GHz and would like to learn more about the buffer issue.How do I design a buffer which:

1.doesn't distort the signal (spoils the harmonic purity)
2.add as less phase noise as possible.
3.doesn't load the resonator
4.provide an amplification (not always necessary)

any suggestions for common configurations?
 

BigBoss

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Re: VCO LC 2.5G hz

roee_by said:
I'm designing a CMOS cross-coupled VCO at 4GHz and would like to learn more about the buffer issue.How do I design a buffer which:

1.doesn't distort the signal (spoils the harmonic purity)
2.add as less phase noise as possible.
3.doesn't load the resonator
4.provide an amplification (not always necessary)

any suggestions for common configurations?
You will use a differential configuration to build-up this VCO.
Then use a differential bipolar/cmos amplifier to boost the output voltage and then use a emitter follower with current source to get the buffered signal.Simple and straight forward.

All circuit topologies will be differential to prevent from noise..
 

dinesh agarwal

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VCO LC 2.5G hz

differential arch ofcourse provide better noise immunity

but what about the supply noise sensitivity
 

BigBoss

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Re: VCO LC 2.5G hz

dinesh agarwal said:
differential arch ofcourse provide better noise immunity

but what about the supply noise sensitivity

If you have an intention to design a VCO, in all even cases you should supply this VCO by a "silent regulator" whatever it's either signle ended or differential.
That's why a silent regulator is a must.

In RFIC, it's not very complicated.A simple curvature corrected bandgap and a opamp with CMOS (or BJT) and a simple feedback.
Of course to ensure the stability a external capacitor...This will work.
 

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