# anyone know bandwidth function in cadence? it seemed wrong!

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#### sunjiao3

##### Member level 5
Hi, dear all.
Are there anyone familiar with the wavescan calculator of cadence? It seemed to be totally wrong. I use it to measure the 3dB bandwidth, whether it is low, high or band, the results go far from the right values. Are there any settings that I should be careful of? Or is it just a wrong function?

And, how do you calculate the bandwidth in ADE?

Kind regards!

Select: Tools > Calculator
From Calculator window: Special Functions > Bandwidth > 3 dB > Select node that you want to calculate BW there.
You should be running AC simulation. (I think transient also may be valid, but not sure, try it)..

I hope that helps you,
Regards,

#### sunjiao3

##### Member level 5
Re: anyone know bandwidth function in cadence? it seemed wro

Thank you for your kindness, but maybe I didn't clearify it. I use the new versions of calculator ---wavescane here. And the bandwidth function is directly listed in it. I use 20dB(Vf (outp)-Vf(outn)) to get the gain. And then, I use the bandwidth function, 3dB, band, however, the result is wrong! Far far from the right value. Have you encounted such problems before?

#### kgl_13gr

##### Member level 5
Use the bandwidth function on the absolute magnitude response, not the one in dB.

Otherwise it calculates the bandwidth as the frequency were the output is 0.707 times the dc gain in dB which is obviously wrong.

#### sunjiao3

##### Member level 5
Re: anyone know bandwidth function in cadence? it seemed wro

Hi, dear all, the following is the answer I got from an AE in cadence, hope it would be helpful.

For your first question, you can ignore 20dB for your output because 20dB is included in bandwidth function. For example, if you want to get the "band" bandwidth, you can directly use the ac magtitude results(mag not dB20). You only need to do in bandwidth configuration is to set the dB number and bandwidth type "band".

Kind regards.

sweet_luoing

### sweet_luoing

Points: 2

##### Newbie level 3
Re: anyone know bandwidth function in cadence? it seemed wro

Hi, dear all, the following is the answer I got from an AE in cadence, hope it would be helpful.

For your first question, you can ignore 20dB for your output because 20dB is included in bandwidth function. For example, if you want to get the "band" bandwidth, you can directly use the ac magtitude results(mag not dB20). You only need to do in bandwidth configuration is to set the dB number and bandwidth type "band".

Kind regards.

Dear Sir,
When I use bandwidth function, it do not show me any figures and values. I perform pss and psp analysis and want introduce an expression for bandwidth of my circuit gain. would you please help me?

#### Dan_Mavencamp

##### Newbie level 1
Re: anyone know bandwidth function in cadence? it seemed wro

If you know the target another way to for a low pass filter is to use the cross function, for example
if the circuit has a 20db gain and you are looking for the 3db bandwidth the following will work

cross((dB20(VF("/outse1")) - 17) 0 1 "falling" nil nil)

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