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AM Modulation. (Read 5930 times)
ic_engr
Senior Member
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Posts: 135
AM Modulation.
Jan 15
th
, 2010, 8:20am
Hello,
I am trying to simulate an effective GSM signal which has GMSK modulation.
What I need to set-up is 1kH AM with 80% modulation on a 900MHz carrier.
Can anyone tell me if I can set this up in Spectre/Cadence using the standard analogLib sources or ahdl models ?
Will greatly appreciate any suggestions.
ic_engr
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pancho_hideboo
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Re: AM Modulation.
Reply #1 -
Jan 15
th
, 2010, 8:39am
ic_engr wrote
on Jan 15
th
, 2010, 8:20am:
I am trying to simulate an effective GSM signal which has GMSK modulation.
What I need to set-up is 1kH
AM
with 80% modulation on a 900MHz carrier.
Is there any relation to
AM
regarding GMSK ?
Do you mean a generation of GMSK by
QAM
?
GMSK is no more than a FSK. But it has amplitude variations due to limited bandwidth.
http://en.wikipedia.org/wiki/GMSK#Gaussian_minimum-shift_keying
http://edocs.soco.agilent.com/display/ads2009/GMSK+Mod
http://edocs.soco.agilent.com/display/ads2009/PtRF+GSM+%28Pwr+Src%2C+RF+Carrier+...
If you use Cadence Spectre, use "rfLib/GSM_xmtr" and "rfLib/IQ_modulator".
If your need is a generation of simple AM signal truely, see the following.
http://www.designers-guide.org/Forum/YaBB.pl?num=1233850018
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«
Last Edit: Jan 15
th
, 2010, 9:43pm by pancho_hideboo
»
Kita━━━━━━(゚∀゚)━━━━━━ !!!!!
http://www7.plala.or.jp/ungeromeppa/flash/kita.html
http://www.youtube.com/watch?v=mjIxGh55bMM&feature=related
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ic_engr
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Posts: 135
Re: AM Modulation.
Reply #2 -
Jan 20
th
, 2010, 5:59am
I did use the GSM_xmt in rfLib in Cadence. However it does not let me control the frequqeuncy. Would you know how I can use it. The only parameter controllable is the 'seed' and the amplitude ?
Notice the GSM has a frequency of 900MHz or 2GHz. I would like to try different frequencies from 900MH to 2.5GHz in my simulation.
Noticing the 'seed' parameter makes me think this is a random number generator.
ic_engr
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pancho_hideboo
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Re: AM Modulation.
Reply #3 -
Jan 20
th
, 2010, 6:03am
Answer my question.
Is there any relation to AM regarding GMSK ?
"rfLib/GSM_xmtr" is baseband I and Q signal generator.
If you use these I and Q signals as RF signal, use "rfLib/IQ_modulator" with "rfLib/GSM_xmtr".
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Kita━━━━━━(゚∀゚)━━━━━━ !!!!!
http://www7.plala.or.jp/ungeromeppa/flash/kita.html
http://www.youtube.com/watch?v=mjIxGh55bMM&feature=related
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ic_engr
Senior Member
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Posts: 135
Re: AM Modulation.
Reply #4 -
Jan 20
th
, 2010, 10:51am
I believe its a constant envelope, therefore, you are right no AM modulation relation exists for GMSK.
ic_engr
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ic_engr
Senior Member
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Posts: 135
Re: AM Modulation.
Reply #5 -
Jan 22
nd
, 2010, 5:34am
The I&Q modulator still does not allow me to specify the modulation index.
ic_engr
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pancho_hideboo
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Re: AM Modulation.
Reply #6 -
Jan 22
nd
, 2010, 5:41am
ic_engr wrote
on Jan 22
nd
, 2010, 5:34am:
The I&Q modulator still does not allow me to specify the modulation index.
It seems you can't understand MSK.
MSK is CPFSK of modulation_index=0.5 constant.
Study basic modulation theory.
http://en.wikipedia.org/wiki/Continuous-phase_frequency-shift_keying#Continuous-...
The following is MSK signal.
http://www.designers-guide.org/Forum/YaBB.pl?num=1195226387
If you would like to vary modulation index, there is an another option of using "ahdlLib/vco", although you can generate any RF modulated signal by using QAM(I/Q Modulator).
See
http://edocs.soco.agilent.com/display/ads2009/MSK+Mod
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«
Last Edit: Jan 22
nd
, 2010, 6:52am by pancho_hideboo
»
Kita━━━━━━(゚∀゚)━━━━━━ !!!!!
http://www7.plala.or.jp/ungeromeppa/flash/kita.html
http://www.youtube.com/watch?v=mjIxGh55bMM&feature=related
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