oscillator design and pcb

[vale]

pcb lay out for ossicilator

Hi all,
I'm new to RF design and need your help. Here are schematic and layout of my 910 MHz feedback oscillator. The layout is unfinished, because I have not mastered the ADS layout function, which is quite different with Protel.

Some questions:
1. How to use the bottom layer (cond2?) as ground plan?
2. How to put a via to connect a pin to ground plan? (plot a circle in hole layer? then how to connect the hole with pin?)
3. Is solder mask layer necessary? How to make it?
4. Where to find an artwork for SMA connector?

I have read ADS documents but get no idea and want a step-by-step tutorial on PCB layout. Please help me! Comments on my osc design are also needed!

Thanks a lot!

 

[Soben]

oscillator pcb

I hope this will help:


1.) U cant use cond2 as bottom ground plane, cond and cond2 are metalization layers of the top plane as far as I know. GRND is regarded as a close boundary in Layout.

2.) Use Via2 (round Via) from the TLines-Microstrip Menu to connect the pin to the ground plane. Set diamaterer for your hole and just export your design with Gerber. I will also suggest your ground Pads to be larger and with more closed holes on them especially the RF ones.

3.) Solder mask is not nesacery, after u finish your design u can just flaten to remove all the hierachical stuff. Then u can delete unesacery layers.

4.) I dont think there is artwork for SMA connection in ADS. But u can make one your self and import it. Depents though how u will connect the SMA to your board.
IF verticaly then u can design one , if horizontaly u dont need to make any artwork at all.

6.) Looking to your Layout i will like to suggest something. Your Transistor looks it has 2 Emmiter pads, is not good practice to connect them toggether with a small wire like u did(u add inductance). I suggest connect each of them separate to the Ground via a Resistor double the size of your design 15 Ohm. Your emmiter ground pads needs to be larger with holes to the ground for proper grounding (that is crusial in any amplifier).

7.) U can use the "T Line microstips" menu on ADS and connect your parts with microstrips directly on Schematics and Autogenerate the Layout ( u need to understand the orientation of components so your placement on the schematic will give u the layout u expect). Try to play a bit and u will get a hold on it. Also that will help to have better results when u try to simulate your Osc. (Dont forget to include your Substrate definition with MSUB). In The end u will need to do some manually work but just to tune things a bit.

8.) I suggest also to use an RFC on the Supply line to avoid unwanted feedback that will make your circuit unstalbe and oscillatory on other frequencies than ones u wanted to oscillate , also some Tantalum 1u and 10u for decoupling of the souply line.


Good luck.

 

[Willem]

+pcb +oscillator

I agree with soben about the link between the emitters, one thing that i have found is that it is not necesary to use the other emitter pad at all. you just use the one in your schematic. the other one you can cut off as close as possible to the device. So you dont even need to ground it.
The reason for the two emitters is when using the device in a amplifier desgin they (the manufacturers)put the emiiters in parallel in order to decrease the amount of parasitic inductance that make the device unstable. Then both must be grounded as close to the device as possible.

Willem