buffer for 18GHz VCO

[transign]

hello,

Which topologies are the most used for this frequency? I saw class A amplifiers and inverter chains used in some papers

Thank you very much for any help!!

 

[BigBoss]

Emitter/Source Follower is frequently used.

 

[biff44]

depends on your reason for buffering it.
If you need more output power, just blast away with some common source fet.
If instead you are trying to buffer the oscillator from a changing load, you want to choose some amplifier with a very small S12.

 

[biff44]

not at 18 ghz, but explains the concept:

Buffer Amplifiers Solve VCO Problems | Maxim Integrated

This article describes VCO application issues such as load pulling, supply pushing, phase noise and affects of radiated energy of near-by power amplifiers (PAs). It is shown how these problems are mitigated by using a VCO buffer to isolate the oscill

www.maximintegrated.com

you COULD use a ferrite isolator!

 

[biff44]

cascode amps are typically used at lower frequency. not sure if you could make a stable one at 18 ghz though.....is this a discrete design or a mmic chip?