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Matching VCO followed by an amplifier stage

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ahmad_abdulghany

ahmad_abdulghany

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Hello,
When I design a VCO followeb by an amplifier stage, Should I match between them whatever is the frquency? Or this will change the oscillation frequency?
I though in that, but if anyone tried it or have previous info about it, then tell me

Regards,
Ahmad,
 

Re: Matching .... ?

When you work in an integrated circuit it is not necessary to match, because the chip works internally in voltage and not in power. In this case after the VCO there is a buffer of divider (to obtain I and Q signal). If you work with discrete components you have to be very attention on this item because if you change the VCO load you change also the oscillation frequency. Usually also in this case it not necessary to match, but not change the VCO load.

By
 
Re: Matching .... ?

i agree with that , it is very importnat not to change the VCO load it can make the VCO not oscillate

khouly
 
Re: Matching .... ?

I guess that if you use a discrete VCO component, it should have some buffer amplifer (with low S12) already integrated with the VCO to make it (more) insensitive to different load impedances. This buffer should have a 50 Ohm output interface. I've mainly worked with on-chip stuff so I really don't know, I'm just guessing here. Anyway, connecting a 50 Ohm device to your discrete VCO should be safe in terms of frequency pulling, oscillation start-up etc.

Regards,
Peter
 
Matching .... ?

Loads change the the frequency of oscillation.Therefore, before optimizing the VCO, the real load should be connected and the matching between the VCO and buffer amplifier must be fixed and optimized.

Otherwise, when you connect your buffer amplifier, the VCO will be drifted by changing load..
 

Re: Matching .... ?

A better term to describe problem solution can be isolation rather than matching.
 

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