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Simulators >> RF Simulators >> QAM modulator
https://designers-guide.org/forum/YaBB.pl?num=1270105534

Message started by jdac_18 on Apr 1^st, 2010, 12:05am

Title: QAM modulator
Post by jdac_18 on Apr 1^st, 2010, 12:05am

I am trying to simulate a QAM modulator in Cadence Spectre.
I have used the random bit generator, verilog 2 verilog 10 bit dacs, and sin and cos vsources. I have a couple of questions:
1. What is the difference between the EVMQam in the calculator for transient analysis and plotting real vs imaginary in envelope analysis?
2. What do the parameters in the root raised cosine filter provided in the rfLib from Cadence mean? I looked at the code and the equations found for the transfer function but I dont see the correlation for frame time and numChipsOut
3. When I simulate using envelope analysis and look at the frequency output of the spectrum I get a sinc function centered at zero with a bandwidth of twice the symbol rate. Should I filter using the SRRC to get -Rb/2 to Rb/2?

Sorry, I am very new to this.
Appreciate any help regarding any of these questions.
Also apologies if this in the wrong section of the forum.

Title: Re: QAM modulator
Post by pancho_hideboo on May 29^th, 2010, 1:32am

It seems no one will reply.

jdac_18 wrote on Apr 1^st, 2010, 12:05am:

I have used the random bit generator, verilog 2 verilog 10 bit dacs, and sin and cos vsources.

What do you mean by "verilog 2 verilog" ?

jdac_18 wrote on Apr 1^st, 2010, 12:05am:

1. What is the difference between the EVMQam in the calculator for transient analysis
and plotting real vs imaginary in envelope analysis?

Use capital letter and small letter correctly.

I can't understand what you want to mean at all ?

First of all, do you correctly understand results of Transient and Envelope Analyses of Cadence Spectre ?
For example, do you correctly understand "envlp_td" and "envlp_fd" ?

You can apply Ocean function, "evmQAM()" for results of both Transient and Envelope Analyses.

Do you understand "Trajectory" and "Constellation" ?
If you use "evmQAM()", you can calculate "EVM" and plot "Constellation".
http://www.designers-guide.org/Forum/YaBB.pl?num=1264511244

But you can also plot "Trajectory" and "Constellation" without using "evmQAM()".

I plot "Trajectory" and "Constellation" without using "evmQpsk()" in the following.
http://www.designers-guide.org/Forum/YaBB.pl?num=1260978648

jdac_18 wrote on Apr 1^st, 2010, 12:05am:

2. What do the parameters in the root raised cosine filter provided in the rfLib from Cadence mean?

I don't use Cadence Spectre for RF design. So I don't know what parameters are provided.

What component do you use in "rfLib" ? Some complex baseband signal generator including "Raised Cosine Filter" ?
What parameters are provided ?

jdac_18 wrote on Apr 1^st, 2010, 12:05am:

3. When I simulate using envelope analysis and look at the frequency output of the spectrum
I get a sinc function centered at zero with a bandwidth of twice the symbol rate.

It is a very natural result. Do you understand "Nyquist Transmission Theory" ?
http://en.wikipedia.org/wiki/Raised-cosine_filter

jdac_18 wrote on Apr 1^st, 2010, 12:05am:

Should I filter using the SRRC to get -Rb/2 to Rb/2?

What purpose do you limit bandwidth to [-Rb/2, Rb/2] for ?
Don't you use complex baseband signal generator including "Raised Cosine Filter" from "rfLib" ?
Again do you understand "Nyquist Transmission Theory" ?