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.

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

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.

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

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

suggest using a BJT for better 1/f noise.

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

rgds

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

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

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

Hi,Willem

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

thanks.