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Simulators >> RF Simulators >> spectrerf EVM simulation help
https://designers-guide.org/forum/YaBB.pl?num=1264511244

Message started by yaly on Jan 26^th, 2010, 5:07am

Title: spectrerf EVM simulation help
Post by yaly on Jan 26^th, 2010, 5:07am

Hi all,

I used spectre envlp analysis to simulate a RF transmitter with a 16QAM input signal. However,when I ploted EVM I got a constellation that is rotated some angles compared with ideal 16QAM, and the 50.3% EVM result is a disaster:-(.

I think the EVM result is deteriorated by the constellation rotation(not sure). So the question is how to rotate the consellation correctly in spectre? In Agilent ADS,some functions can be used to change the angle part of a complex signal so you can rotate the constellation as you wish. But how to do this in spectre? Can anyone give me some suggestions?

Thanks,
yaly

Title: Re: spectrerf EVM simulation help
Post by pancho_hideboo on Jan 26^th, 2010, 5:15am

yaly wrote on Jan 26^th, 2010, 5:07am:

In Agilent ADS,some functions can be used to change the angle part of a complex signal so you can rotate the constellation as you wish.
But how to do this in spectre?

It has no relation to Cadence Spectre.
It is a task in Cadence Post Processing Environment not Cadence Spectre.

It is same as in Agilent ADS Post Processing, although I don't know what method you use for plotting constellation.

Quote:

M_PI = acos( -1.0 )
M_TWO_PI = 2.0 * acos( -1.0 )
j = complex( 0.0, 1.0 )
Angle_deg = 12.0
RFsig_1st = harmonic( v( "/RFsig", ?result "envlp_fd" ), 1 )
RFsig_1st_rotated = exp(j*Angle_deg*M_PI/180.0) * RFsig_1st

I have a question.

We can't include noise effects due to signal path NF and local phase noise in Envelope Analysis of Cadence Spectre.
http://www.designers-guide.org/Forum/YaBB.pl?num=1260978648/1#1

We can only consider AM/AM and AM/PM nonlinearity in Envelope Analysis of Cadence Spectre.
But your constellation is fairly scattering, regardless of non considering noises.

Why is your constellation fairly scattering ?

The following is a case which have only AM/AM nonlinearity without AM/PM and noise effects.
http://www.designers-guide.org/Forum/YaBB.pl?num=1216663909/5#5

In Agilent GoldenGate, we can consider local phase noise effects for EVM by using "NOISECOR: File-based Correlated Noise Source" as well as NF effects of signal path.

Title: Re: spectrerf EVM simulation help
Post by yaly on Jan 26^th, 2010, 8:48pm

I simply use direct plot form in ADE as show below because I'm not so familiar with cadence post procesing or OCEAN functions. When wavescan is used to plot the constellation,the EVM value is calculated automatically. However, I don't know how spectre calculate it.

Thank you pancho_hideboo, seems it's time for me to step into OCEAN.

Title: Re: spectrerf EVM simulation help
Post by pancho_hideboo on Jan 26^th, 2010, 9:04pm

yaly wrote on Jan 26^th, 2010, 8:48pm:

I simply use direct plot form in ADE as show below because I'm not so familiar with cadence post procesing or OCEAN functions.

Activate "Add to Outputs".
If do this, you can modify equations as rotated.
But I recommend you to write out Ocean Script from ADE and modify it.

yaly wrote on Jan 26^th, 2010, 8:48pm:

When wavescan is used to plot the constellation,the EVM value is calculated automatically.
However, I don't know how spectre calculate it.

Still you are misunderstanding.
Task of calculating EVM is Post Processing not Cadence Spectre.
Ocean function, evmQAM() is used.

We can use Agilent Post Processing Environment for results of Cadence Spectre.
For example, you can use a following function for evaluating EVM from Cadence Spectre results.
http://edocs.soco.agilent.com/display/ads2009/const+evm%28%29#constevm%28%29-1106089

Vice versa, we can use Cadence Post Processing Environment for results of Agilent ADSsim(RFDE) or Agilent GoldenGate.

Whatever vendor's simulator you use, results from it are no more than numeric data.
You can do post processing by using any Post Processing Environment as far as you can read data.

See the following. I'm using Agilent Post Processing Environment for results of Synopsis HSPICE.
http://www.designers-guide.org/Forum/YaBB.pl?num=1264059467

See the following. I'm using Cadence Post Processing Environment for results of Agilent GoldenGate.
http://www.designers-guide.org/Forum/YaBB.pl?num=1260978648

Attached is a special Ocean function for EVM from "blk" format data of Agilent GoldenGate.
We can use even this function for both Agilent ADS results and Cadence Spectre.

Title: Re: spectrerf EVM simulation help
Post by yaly on Jan 27^th, 2010, 5:14am

Thanks a lot ,pancho_hideboo. Your answer is very helpful. I was not clear about the difference between spectre and cadence post processing before. Still learning now...