# Constant Envelope Modulation Using Non-Linear Power Amplifie - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Original posts:

Waverider
 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

Waverider
 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.

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

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. _________________Best regards, - IR

Posted  11/12/2012

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