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Constant Envelope Modulation using Non-Linear Power Amplifie - RF Cafe Forums

Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views. It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if you would like to post something on RF Cafe's Facebook page, please do.

Below are all of the forum threads, including all the responses to the original posts.


 Post subject: Constant Envelope Modulation using Non-Linear Power Amplifie
Posted: Tue Jun 21, 2011 6:20 am 
 
Captain

Joined: Sat Apr 22, 2006 2:37 am
Posts: 6
Location: SoUtH EaSt of AsIa
As we know, we like to utilize the power amplifier in non-linear/saturation region for its maximum power efficiency.

We also know that only constant envelope modulation scheme can use non-linear power amplifier.

So my questions are:

1. Are basic form of BPSK and QPSK (without pulse shaping) considered constant envelope modulations?

2. If they are constant envelope modulation schemes, we can employ a non-linear power amplifier.
Knowing that besides amplitude distortion a non-linear amplifier can introduce, it can also produce phase distortion on the output signal.
So for PSK modulation where information is modulated in the phase, won't a non-linear amplifier distorts the phase and hence information?

Pls help solve my confusion.

Tee


 
   
 
 Post subject: Re: Constant Envelope Modulation using Non-Linear Power Ampl
Posted: Tue Jun 21, 2011 9:31 am 
 
Captain

Joined: Sat Apr 22, 2006 2:37 am
Posts: 6
Location: SoUtH EaSt of AsIa
I think I got my answer, any form of PSK (BPSK or QPSK) is not supposed to be constant envelope.

So this nulls all the questions I posted.


 
   
 
 Post subject: Re: Constant Envelope Modulation using Non-Linear Power Ampl
Posted: Thu Jun 23, 2011 1:54 pm 
 
Site Admin
 

Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany
Constant envelope signals can also be distorted in linear PA. It depends on what is the maximal ouptput power compared to the P1dB of the given amplifier.

Phase distortion and amplitude distortion goes hand in hand. They can be measured by Vector Signal Analyzer under average power conditions, it is named EVM which is a vector contains phase and magnitude.

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- IR





Posted  11/12/2012
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