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Using Simulink  to model a  RF transceiver (Read 21033 times)
AnalogAroma
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Using Simulink  to model a  RF transceiver
Feb 06th, 2009, 6:10am
 
Hi Everybody,

        I have been experiencing some problems to model a RF transceiver in  Simulink. My baseband signal has a BW of  4MHz. But when I upconvert this signal at 1GHz , the shifted baseband signal spectrum seems very strange !!

Any simulink expert available in this forum ?
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pancho_hideboo
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Re: Using Simulink  to model a  RF transceiver
Reply #1 - Feb 6th, 2009, 7:17pm
 
AnalogAroma wrote on Feb 6th, 2009, 6:10am:
I have been experiencing some problems to model a RF transceiver in  Simulink.
My baseband signal has a BW of  4MHz. But when I upconvert this signal at 1GHz , the shifted baseband signal spectrum seems very strange !!

Show me your block diagram of Simulink and resulting Spectrum.

How to model upconverter in Simulink ?
Just simply multiplier ? Or using Mixer in RF block set ?

Which of model in the followings do you use ?
(1)BB-Signal, I(t)+j*Q(t) ---> Real RF Signal, (I(t)+j*Q(t))*exp(j*omega0*t)
(2)BB-Signal, I(t)+j*Q(t) ---> Equivalent Lowpass Representation of RF Signal, {I(t)+j*Q(t), omega0}

What solver do you use in Simulink ?
Continuous or Discrete ?
What time step control do you use ?

If you use (1), time step is enough small ?
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« Last Edit: Feb 7th, 2009, 4:52am by pancho_hideboo »  
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AnalogAroma
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Re: Using Simulink  to model a  RF transceiver
Reply #2 - Feb 10th, 2009, 1:45pm
 
Show me your block diagram of Simulink and resulting Spectrum.
------------
AA :  Please see the attached file.  A pdf file containing the spectrums will be added later.
-------------------------------
How to model upconverter in Simulink ?
Just simply multiplier ? Or using Mixer in RF block set ?
------------------------------------------
AA: I have used a multiplier.

----------------------------------------------
Which of model in the followings do you use ?
(1)BB-Signal, I(t)+j*Q(t) ---> Real RF Signal, (I(t)+j*Q(t))*exp(j*omega0*t)
(2)BB-Signal, I(t)+j*Q(t) ---> Equivalent Lowpass Representation of RF Signal, {I(t)+j*Q(t), omega0}
--------------------------------------
AA: Method  1 , real RF signal.
------------------------------------
What solver do you use in Simulink ?
Continuous or Discrete ?
-------------------------------------
AA : Discrete
-------------------------------------
What time step control do you use ?
If you use (1), time step is enough small ?
------------------------------------
AA :  Variable time step.  Max time step is auto.  I have also used
10 ps , but no improvement !
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pic_RF_Xcvr.jpg
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AnalogAroma
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Re: Using Simulink  to model a  RF transceiver
Reply #3 - Feb 10th, 2009, 1:48pm
 
pancho_hideboo wrote on Feb 6th, 2009, 7:17pm:
AnalogAroma wrote on Feb 6th, 2009, 6:10am:
I have been experiencing some problems to model a RF transceiver in  Simulink.
My baseband signal has a BW of  4MHz. But when I upconvert this signal at 1GHz , the shifted baseband signal spectrum seems very strange !!

Show me your block diagram of Simulink and resulting Spectrum.

How to model upconverter in Simulink ?
Just simply multiplier ? Or using Mixer in RF block set ?

Which of model in the followings do you use ?
(1)BB-Signal, I(t)+j*Q(t) ---> Real RF Signal, (I(t)+j*Q(t))*exp(j*omega0*t)
(2)BB-Signal, I(t)+j*Q(t) ---> Equivalent Lowpass Representation of RF Signal, {I(t)+j*Q(t), omega0}

What solver do you use in Simulink ?
Continuous or Discrete ?
What time step control do you use ?

If you use (1), time step is enough small ?


The signal spectrums are shown in the attached pdf file.
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pancho_hideboo
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Re: Using Simulink  to model a  RF transceiver
Reply #4 - Feb 12th, 2009, 7:16am
 
Maybe due to rate mismatch between BB and LO signals.
Insert upsampler for BB or set upsample ratio in raised cosine filter.
If you upload your block dirgram, I can modify.
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AnalogAroma
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Re: Using Simulink  to model a  RF transceiver
Reply #5 - Feb 12th, 2009, 7:26am
 
Thanks a lot for your kind feedback.  The zipped Simulink model is attached herewith.
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pancho_hideboo
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Re: Using Simulink  to model a  RF transceiver
Reply #6 - Feb 13th, 2009, 8:58am
 
Frame time lengths before mixer are different in your setting while you use frame-based sampling mode.
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« Last Edit: Feb 14th, 2009, 4:28am by pancho_hideboo »  

your_mixer.jpg
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pancho_hideboo
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Re: Using Simulink  to model a  RF transceiver
Reply #7 - Feb 13th, 2009, 8:59am
 
This is my setting.
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my_mixer.jpg
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pancho_hideboo
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Re: Using Simulink  to model a  RF transceiver
Reply #8 - Feb 13th, 2009, 9:04am
 
These are results of spectrum.

Why do you set LO frequency as 1GHz ?
In simulink model, you don't have to set LO frequency as real frequency.
So you should use Equivalent Lowpass Representation of RF Signal or low frequency as LO.
 BB-Signal, I(t)+j*Q(t) ---> Equivalent Lowpass Representation of RF Signal, {I(t)+j*Q(t), omega0}
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my_mixer_spectrum.jpg
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AnalogAroma
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Re: Using Simulink  to model a  RF transceiver
Reply #9 - Feb 14th, 2009, 3:33am
 
Wow ! Your simulation results look fantastic. I want to use your settings  to do simulate  the transeiver in my office computer.

But from the last Thursday evening, I have been sick and will not go to the office for several days.  After  my recovery, I will post my replies again.
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AnalogAroma
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Re: Using Simulink  to model a  RF transceiver
Reply #10 - Mar 11th, 2009, 9:46am
 
Hi PH,

    I am back from  the hospital. After following your setting , I have got properly upconverted spectrum. Howerver, I can not zoom the spectrum.
I have played with several options, but the spectrum resolution is not as good as yours.  Which setting have you used in the fft plot ?  May I have a look and run you Simulink file on my side ?
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pancho_hideboo
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Re: Using Simulink  to model a  RF transceiver
Reply #11 - Mar 13th, 2009, 9:10am
 
AnalogAroma wrote on Mar 11th, 2009, 9:46am:
Hi PH,
Who is he ? Don't use unfamiliar abbreviations. I don't like very local abbreviations such as "U R right", "Do U", "thank u", "BR", "ViVA, ADE, CDF of Cadence", etc.

See attached model of Simulink.
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AnalogAroma
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Re: Using Simulink  to model a  RF transceiver
Reply #12 - Mar 13th, 2009, 4:34pm
 
Hi   Pancho_hideboo,

         After applying  your Spectrum scope settings , I have got really cool
spectrums !!   Now , modelling in Simulink seems to be enjoyable.
Thanks a  lot to dispel my initial frustration with Simulink !
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