problem with a colpitts VCO in ADS

[E-design]

It is the same as in my first diagram (100M, order 5)
I just tested the circuit with 68nH with 4.7pF feedback & load cap. It oscillates at about 87MHz @ 8dBm level.

Make sure when you get the graph data to use the HB.Vout data and plot vs frequency in a dBm vertical scale.

What error do you get in the simulator status box?

 

[asoom]

i don't get any error in the simulation. actually the simulation ends successfully.
the problem is that when i plot Vout vs freq, it gives only a dc component, which means that the output is dc voltage.

does Vout differs from HB.Vout? coz i don't have HB.Vout within the parameters to be plotted, i have Vout instead?

i used 4 khz for freq[1] and 10 for order[1], since i read in one of the HB tutorials that "For a single tone HB simulation, set the Frequency to the fundamental frequency of the source used in the circuit." here are the time domain representations and the spectrums that i obtained for Vout and I_Probe1 when i ran the simulation. for me they are not expected at all.

by the way i tried the simulation with 100MHz for freq[1], the results were worse. and i got a warning for that in the simulation box.



Added after 5 hours 2 minutes:

if the results are not clear enough in the image. here is the image uploaded again.

 

[manish12]

i am using ADS2004A, in that the transistor of given name is not available , what other transistor i can you for this VCO, if not possible , can you give me the lib of this transistor ?

[with given ckt with different transistor not working , compared from given wave form.]

thank you.

 

[asoom]

this transistor is from the RF_transistor_library. if it's not available you can use the transistor that E-design used in his schematic above.

 

[E-design]

I suggest you do it in stages. Get the RF carrier to simulate first and make sure you see the spectral components. Then start with the baseband modulation. You have to use the envelope simulation controller to see the modulation bandwidth. Normal HB won't show this.

 

[asoom]

i tried to simulate the oscillator part for my circuit such as you did before, the output was DC! i even changed my components values so that they are identical to yours but Vout remained DC! i simulated the same oscillator you simulated and am not getting any change in Vout above 9V like yours! what's the problem?

Added after 22 minutes:

sorry if am asking alot, but i need to get results for my simulation very soon, coz i have to submit them on sunday. so am running out of time and am not getting any expected output! even for that simple oscillator part.

i need also to translate this circuit on PCB in ADS. if anybody can guide me in that, or have any useful resource. i'll be soooo thankful.

 

[E-design]

You must be setting up something wrong. Post your revised circuit so we can check.

 

[asoom]

i have asked my teacher and he told me that i have to add an oscport. this must be added to the feedback of the oscillator.

i checked some schematics of oscillators in ADS and an oscport was there in all of them. when i implemented my schematic the first time i added an oscport but i removed it because it caused and error and i didn't know how to eliminate it. now i tried to add it both in parallel and in series to the 4.7 capacitor but the error appeared again. do you have any idea where to add it?

if the oscport is really the problem with my circuit, i wonder how you got your results without adding it. any way here is my revised circuit.

 

[E-design]

Osc port is not always needed. I can't open your file. Post a GIF capture of your latest circuit

 

[asoom]

it is the same as the first one, but i modified the lc values.

 

[asoom]

you can open the design file by first extracting it, then open a new project in ADS and use 'copy design file' to copy the extracted design file into your project networks folder.

 

[tyassin]

Hi

You need to move your Vout to under the inductor(collector of the transistor).
As it is now you will mesure 9V what ever you do, because Vout is measured over your DC supply!!!
I mentioned this in a previous post.

kind regards

 

[asoom]

thanx alot, i didn't understand your first post. if only i did, this would save alot of time on me. really thanx to you tyassin and to E-design for your help.

now i need to implement this schematic on a PCB in ADS. if anyone can guide me or have a useful guide or tutorial on that i'll be thankful.

 

[asoom]

can't anybody tell me how to implement my schematic on PCB in ADS?
plz help, i need this very soon.