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passerby
Joined: 12 Jun 2006
Posts: 46
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 06 Jul 2009 18:19 power amplifier backoff |
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In some articles it said the power "back-off" for the power amplifier can
conserve battery power and avoid to cause interference in the adjacent
channels. It also says the efficiency will be reduced? why?
Could someone advise what "Back-off" mean here?
Please kindly advise and thanks for the help.
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vfone
Joined: 10 Oct 2001
Posts: 2328
Helped: 327
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06 Jul 2009 20:04 back off+power amplifier |
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Back-off power means reduction of the output power when reducing the input power.
The efficiency of the power amplifier is reducing when back-off the output power, because the amplifier goes deeper into the linear region.
Linear power classes (e.g. class-A) are less efficient that nonlinear power classes (e.g. class-B) due to higher conduction angle.
Read: RF Power Amplifiers for Wireless Communications – S. Cripps
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kspalla
Joined: 19 Aug 2008
Posts: 848
Helped: 140
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07 Jul 2009 5:47 maximum linear power definition |
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in other words,
Let say amplifier has p1dB of 10W but when it is used for certain linear applications the same amplifier is used to give may be 4W output.
Some applications this 4W is average power but its peak can go to 10W due to PAR.
If selected 4W amplifier for this purpose the amplifier will produce the IMDs.
So 10W amplifier that gives only 4W under normal operation is less efficient.
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Chinaski
Joined: 17 May 2001
Posts: 217
Helped: 5
Location: Spain
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07 Jul 2009 9:34 power back-off |
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Hi kspalla
Your explanation is good but I think that someone who doesn't know what does back-off mean is not going to understand P1dB, PAR and IMD acronyms.
For passerby: You should follow vfone's advice: Cripps book rules 
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flyhigh
Joined: 12 Nov 2003
Posts: 561
Helped: 32
Location: somewhere over the rainbow
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08 Jul 2009 9:03 definition of back off power |
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Hi
An amplifier would be typically used in back-off regime when signal is modulated using some spectrum efficient techniques that is in turn sensitive to nonlinearities.
An example of such a modulation could be OFDM modulation. In its raw version, it is not well characterized by average power as for some symbols peak power could be up to 6dB higher than the average. For these peaks, the nonlinearities have more severe effects than if only average power is considered, so one should "back off" from using maximum linear power of the amplifier (defined as 1dB compression point) and use 3-6 dB less, depending on the system under consideration.
flyhigh
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08 Jul 2009 9:03 Ads |
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cnuchcnu
Joined: 24 Oct 2009
Posts: 4
Location: calicut
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25 Oct 2009 17:40 "Back-off" for power amplifier |
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hi to all,
i am doing project on MIMO SFBC CI OFDM. please will you say how to implement receiver part in MATLAB.
please will you forward any matlab code related to this. At least will you send steps for implementing this.
thank you very much in advance.
Regards
srinivas
srinivasarao473(at)gmail.com
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