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How to plot power in dBm using Calculator of Spectre

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DoYouLinux

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Hi all,

It seems easy, but I could not make it anyway.

As you might know already, in Cadence Spectre, we can plot the spectrum of a signal (say, output of an amplifier) using "dft" function of the Calculator. But, this gives the magnitude of the result in Volt. When I use "dBm" function, it gave me wrong calculation which did not correspond to the value of conversion from Volt to dBm. Also, I could not find the definition of the function "dBm" and also no specification for the reference resistance ...

Could anyone suggest me how to plot the spectrum in dBm on the Y axis please ??

Thanks a lot in advance :)

DYL
 
DoYouLinux said:
As you might know already, in Cadence Spectre,
we can plot the spectrum of a signal (say, output of an amplifier) using "dft" function of the Calculator.
Click to expand...
Don't mix up Simulation with Post Processing. They are completely different phase.
It is an issue of Cadence Post Processing Environment and has no relation to Cadence Spectre at all.

DoYouLinux said:
When I use "dBm" function, it gave me wrong calculation which did not correspond to the value of conversion from Volt to dBm.
Also, I could not find the definition of the function "dBm" and also no specification for the reference resistance ...
Could anyone suggest me how to plot the spectrum in dBm on the Y axis please ??
Click to expand...
Arguments of dBm() function in Agilent Post Processing Environment are Voltage and load impedance.
While argument of dBm() function in Cadence Post Processing Environment is Power.
For example, you have to set "dBm()" like following in Cadence Post Processing Environment.
dBm( mag(Vout)**2/(2*Rload) )

See https://www.designers-guide.org/Forum/YaBB.pl?num=1258711688/1#1

Also see https://www.designers-guide.org/Forum/YaBB.pl?num=1264078706/4#4
 
Last edited:
Hi Shahbaz.ele: thank you very much for your reply. However, the Calculator means a tool in Cadence.

Hi pancho_hideboo sensei, long time no see. Thank you very much for your explanations. I will try this and will give my feedback very soon.

Thanks a lot guys,

DYL
 

You want to do the conversion of volts into power. If you do this you have to take care of the impedance, typically it would be 50 Ohm, but you have to check, especially when you use a build in function.
But perhaps you can do the calculation by yourself:
Power = Volts^2/impedance
dBm = 10*log(Power/1mW)
 

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