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[SOLVED] How to couple noise to a voltage signal?!

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smn_eb

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Hi Everybody,

I need to simulate a radar system in which the VCO is fed by a ramp voltage. I simulated with an ideal ramp signal, now I want to add noise to my ramp so it wouldn't appear smooth on its edge, but I'd want it look uneven. I put a voltage noise source in series with my ramp source but it didn't work, the only thing it gives out is just noise. What I want to see is a ramp voltage coupled with noise. Could anyone help me please?

Thanks,
 

I would think your series noise source would work. What are you using to simulate? You could try putting the noise source in parallel with the ramp, through summing resistors,
 
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    smn_eb

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Since the noise voltage is so small, it may not be visible on the ramp signal but if you do a Phase Noise simulation, the effect of this noise contributor will absolutely be seen on the Phase Noise side-bands.
You don't have to use a ramp signal, a simple DC voltage applied to the VCO with a series connected noise signal source will contribute into the signal performance.
 
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    smn_eb

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Thank you all, the problem is solved. I'm running Envelope simulation and it seems I needed to care about the noise bandwidth when I was setting voltage noise source. The problem was that when I give 1mV as the noise voltage what I get at the output is something in the range of 500 V!!! I think it was because of the bandwidth which I didn't consider. Because the dimension for the noise voltage is not Volts but Volts/square root Hz. And because the output noise was very big, it didn't let the main signal show up!
Thanks
 

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