gsm vco

I want to build a relatively high power VCO in the GSM band (880-890 MHz and 925-935 MHz) ....

Anysuggestions?
Thanks in advance,
Ahmad,

there is a example
http://www.eetchina.com/ARTICLES/200...T_RFT_AN01.PDF
how?

first, thanks for contribution,

But, How what? I didn't get it..

Another thing, I hope i can find a VCO with non-surface mount components, can't i find such VCO?

What's the advantages of SMD over through hole components?!

Regards,
Ahmad,

I believe u need to use SMD at 900 MHZ even for lower freq, lead inductancies will have quite an effect in the operation of your circuit. SMD has much less parasitics than convetional components.

Regarding your VCO i will give u some ideas.

1.U need a linear Amplifier, Class A will do, use BJT transistors, try to find a BJT that will give you a high P1dbm.

2. A tunable resonator, for that u need a Varactor Diode, the capacitance of your diode depents from your application.

basically with an amplifier and a resonator in a closed loop if u have a total phase shift of 360 u get an oscillator.

Some examples using ads u can find at:

http://www.odyseus.nildram.co.uk/RFM...cuits_Page.htm

Thanks Soben,

I belive you now concerning SMD, as I built one with normal components (R's,C's, air core coil, and BJT of GBW=2.2GHz) and it didn't work at all, I was scanning all the range from 100MHz to 3GHz on the 3.3GHz spectrum analyzer, but i didn't find anything,

Now, I want to build another one with SMD

But the problem is I may not able to replcace diodes and BJT with surface mount ! and for the coil, I need its value to be 7nH, what's the best choice to build it? In the previously made circuit, i made it 3 windings of a 1mm diameter cupper wier on air core radius of 4mm, is that correct?

And finally, for the VCO you sent link of, it uses AT41486 BJT with ft ≈ 6GHz, in my case, i can't get that transistor, I may have maximum ft of 2.2GHz.. Will this affect alot?

Thanks for help,
Ahmad,

Your can find for both the BJT and the diode in a sourface mount version, try philips semiconductors and i am sure your will find what u need. I recomend again silicon varactors

Coil craft air core inductors will give u high Q value and will be fine. They provide free Samples so no need to make one.

Did u measure S11 at 100Mhz to see if u get what u design ? Better measure it at your frequency of operation. What is the Q of your coil ? U need a high Q coil, since the varactor will degrade the total Q of your resonator.

Dont need to use the Agilent transistor, a Philips one will be fine i recomend, and FT of 6-7 GHz. For your transistor with FT 2.2 GHz what is S21 at your operatiing frequency ? do u have enough gain to make it oscillating or u need to cascade 2 of them? Your amplifier should be a bit broadband so higher FT is required. Open loop gain should be higher than 1 to have it oscillating.

If your circuit is not oscillating again the reasons may be not enough gain to start the oscillation or u dont have 360 deg feedback. Try to simulate your circuit including all the paracitics since they have an importan role in the final outcome.

Dear,

Check Minicircuits & Synergy Microwave Sites.They have attractive VCO chips.

Minicircuits : www.minicircuits.com
Synergy : www.synergymwave.com

Good Luck.