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Frequency spectrum in ADS

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prafuldeo

prafuldeo

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Hello friends,

I have started to work on RF System design on ADS and I am new to it. I have designed a simple VCO (Fig.1) and can get the output signal in time domain (time vs voltage, Fig.2). I am however, cannot get the correct spectrum on frequency domain (dB vs frequency, Fig.3). How can I get it?

Many thanks
 

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  • Fig.1-vco circuit.jpg
    Fig.1-vco circuit.jpg
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  • Fig. 2-vco output.jpg
    Fig. 2-vco output.jpg
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  • Fig.3-desired output.jpg
    Fig.3-desired output.jpg
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For example, run a harmonic balance simulation, or as starting point: convert your time domain signal into the frequency domain: fs(real(vout[0])) or db(fs(real(vout[0])))
 

johnjoe said:
For example, run a harmonic balance simulation, or as starting point: convert your time domain signal into the frequency domain: fs(real(vout[0])) or db(fs(real(vout[0])))
Click to expand...

Sorry it may sound dumb but how can I do it? In equation editor?

How can I see this in HB simulation? I did run HB simulation but cant get the spectrum.

Thanks
 

Yes, the conversion from time to frequency domain can be realized in the dataset window, e.g in your second picture above just change real(vout[0]) to fs(real(vout[0])).
If you ran HB sim correctly, you should be able to plot voltages in the dataset window as function of frequency.
 

johnjoe said:
Yes, the conversion from time to frequency domain can be realized in the dataset window, e.g in your second picture above just change real(vout[0]) to fs(real(vout[0])).
If you ran HB sim correctly, you should be able to plot voltages in the dataset window as function of frequency.
Click to expand...

Many thanks !

I tried the same method for this other circuit (see figures) but not able to get the frequency spectrum results. Could you comment on it?

Thanks
 

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  • Fig.1-circuit.jpg
    Fig.1-circuit.jpg
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  • Fig. 2-output.jpg
    Fig. 2-output.jpg
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Just don't plot TRAN... signals, use HB... signals from the dataset.
 

You can use fs() function in data display.More info is found in help..
HB may not work in that case because steady-state regime is not established due to ON/OFF signals.
 

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