How to select a transistor for S-band local oscillator ?

[ahmer saeed]

Designing an oscillator

I am selecting a transistor for designing S-band local oscillator. What parameters I have to keep in mind for the selection.Whether I should select SiGe BJT or GaAs FET or pHEMT for oscillator. If you have an experience of designing an oscillator, what transistor have you preferred in designing.

 

[radiohead]

Re: Designing an oscillator

BJT is to be preferred because it has lower 1/f noise. This results in better oscillator phase noise.

 

[DJ]

Re: Designing an oscillator

What applications?
For best phase noise SiGe HBT might be the best. If you can't find take a BJT.
Use 681 of Nec for a start point.

 

[springf2000]

Re: Designing an oscillator

the low phase noise is important to VCO,so the low noise is important

 

[helio1972]

Re: Designing an oscillator

do you have an example on ADS for an oscillator using a FET ? if so don't hesitate to send me it asap
thanks in advance

 

[sgperzoid]

Re: Designing an oscillator

suggest using a BJT for better 1/f noise.

I think overall noise figure is a key FOM in selecting the device

rgds

 

[alatriste]

Re: Designing an oscillator

Hi,
I advise transistor from Infineon in example BFP640 in SiGe,
this transistor has a very low NF and a low 1/f noise.
If you use a simulator i will need a good characterization of 1/f noise.
Transistor from in SiGe from infineon have colpete Spice models .

good luck

 

[Soben]

Re: Designing an oscillator

I suggest BJTs Philips or Infineon Transistors. Preferably the One that will give you the highest Output power with no matching.

 

[Willem]

Re: Designing an oscillator

The BFP420 is an excellent choice. It has more than enough gain at the frequency you intend to design at. I used it in a 4 GHz oscillator and it works fine. The older versions of ADS does not have the S-parameter model of the device but you can get it from infineon. Thats the way i did it.

Hope you come right.
Willem

 

[cuizw]

Re: Designing an oscillator

Hi,Willem

How is your vco's phase noise perfomances at the offset frequency of 100kHz and 1MHz from the carrier frequency?

thanks.