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Noise Simulation of DAC+VCO

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niteshtripathi

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Hi all,

I have to do noise simulation of DAC+VCO. So I am doing Pss-Pnoise simulation. For DAC, there is witch capacitor circuit, and input of the DAC are clock signal and trim bit (according to which DAC output voltage get set). According to the DAC output voltage VCO gives a output frequency. I am confused how to do the noise simulation of this schematic and what should be the setting in the Pss-Pnoise simulation. What should be the beat frequeny because there is two clock one for DAC and one generated from VCO.

Any lead will be appreciated. Thanks in advance.
 

According to the DAC output voltage VCO gives a output frequency.
You can do VCO simulation with static DAC at most.

If you want to care dynamic effect of DAC to VCO such in Delta-Sigma-Fractiona-N Synthesizer, you have to use Transient Noise Analysis.

What should be the beat frequeny because there is two clock one for DAC and one generated from VCO.
Use correct terminology, there is no "beat frequency", if you use Cadence Spectre.
See https://www.designers-guide.org/Forum/YaBB.pl?num=1268969030/7#7

VCO is a autonomous circuit.
On the other hand, DAC is a driven circuit.

Common divisor between two frequency can never exist.
Quasi-Autonomous HB Analysis can not apply to DAC + VCO.

And you can not understand Pnoise analysis is no more than small signal noise.

If your concerns are small signal noise,
first evaluate noise PSD of DAC alone using Shooting-PSS+Pnoise,
then apply this noise PSD to ideal voltage source,
do HB-PSS+Pnoise simulation of VCO with this ideal voltage source having noise PSD instead of DAC.
 
Last edited:

Thanks alot pancho_hideboo.

I am trying this. And thanks alot for your valuable time. It means alot to me.

You can do VCO simulation with static DAC at most.

If you want to care dynamic effect of DAC to VCO such in Delta-Sigma-Fractiona-N Synthesizer, you have to use Transient Noise Analysis.

Use correct terminology, there is no "beat frequency", if you use Cadence Spectre.
See https://www.designers-guide.org/Forum/YaBB.pl?num=1268969030/7#7

VCO is a autonomous circuit.
On the other hand, DAC is a driven circuit.

Common divisor between two frequency can never exist.
Quasi-Autonomous HB Analysis can not apply to DAC + VCO.

And you can not understand Pnoise analysis is no more than small signal noise.

If your concerns are small signal noise,
first evaluate noise PSD of DAC alone using Shooting-PSS+Pnoise,
then apply this noise PSD to ideal voltage source,
do HB-PSS+Pnoise simulation of VCO with this ideal voltage source having noise PSD instead of DAC.
 

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