Electronics World Cover,TOC,and list of posted Popular Electronics articles QST Radio & TV News Radio-Craft Radio-Electronics Short Wave Craft Wireless World About RF Cafe RF Cafe Homepage RF Cafe in Morse Code Google Search of RF Cafe website Sitemap Electronics Equations Mathematics Equations Equations physics Manufacturers & distributors Engineer Jobs Twitter LinkedIn Crosswords Engineering Humor Kirt's Cogitations Engineering Event Calendar RF Engineering Quizzes AN/MPN-14 Radar 5CCG Notable Quotes App Notes Calculators Education Magazines Software,T-Shirts,Coffee Mugs Articles - submitted by RF Cafe visitors Simulators Technical Writings RF Cafe Archives Test Notes Wireless System Designer RF Stencils for Visio Shapes for Word Search RF Cafe Sitemap Advertising Facebook RF Cafe Forums Thank you for visiting RF Cafe!

Avoiding Saturation (Simple Question) - RF Cafe Forums

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

Amateur Radio | Antennas | Circuits & Components | Systems | Test & Measurement


alyoshak19
Post subject: Avoiding saturation (simple question) Posted: Tue Nov 03, 2009 12:11 pm

Lieutenant

Joined: Tue Nov 03, 2009 12:02 pm
Posts: 1
Hi board,

I'm new to this, so please bear with a simple question. I want to run an RF signal through the linear range of a power amplifier, but at as high a power as possible. It's a complicated signal (sum of FM signals), which is why I want to keep it in the linear part of the transfer curve. Say the PAR is 9 dB. How far away from the P1dB point do I have to back away to completely avoid saturation? Someone was telling me that since a pure sine wave has a 3 dB PAR, you only need to back off (in this case) 6 dB from the P1dB point. Is that true? If so, does this hold in general: if your signal's PAR is x dB, you will avoid saturation at P1dB - (x-3)?

Thanks for any help you can provide (and please don't hesitate to ask for more details -- I just don't know what you need to know).


Top

IR
Post subject: Re: Avoiding saturation (simple question)Posted: Wed Nov 04, 2009 4:50 pm

Site Admin


Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany
Hello,

First, the values that were told you about sine wave are true, because for sine wave the RMS values for voltage and current are 0.707... (1/v2) and if you multiply current and voltage then you will get 0.5 for average power which is then 3dB of the peak power.

The back-off which yields better linearity always contradicts with the requirement for efficiency. If your PA does not have restirctions on the efficiency (No problem of over heating, limited supply voltage source etc), then a reasonable value for backing off would be 6dB away from saturation level, that means let's say: if your P1dB=+50dBm, Psat=+52dBm,
PAR= 9dB, then your peak output power should be not more than +46dBm, therefore you keep a margin from saturation and from 1dB compression point. If you have non-linear large-signal models for your power devices, then you can simulate the operation of the device under such power conditions and see the spectral growth of the 3rd, 5th...harmonics. By this you can consider if this margin is enough for your design or you need additional back-off.

If efficiency is a requirement for your design, then you need to reduce the back-off to minimum. In this case the peak output power should be +50dBm.

I hope this helps!

_________________
Best regards,

- IR



Posted  11/12/2012

RF Cafe Software

   Wireless System Designer - RF Cafe
Wireless System Designer

RF & EE Symbols Word
RF Stencils for Visio
Calculator Workbook
RF Workbench
Smith Chartâ„¢ for Visio
Smith Chartâ„¢ for Excel

About RF Cafe

Kirt Blattenberger - RF Cafe WebmasterCopyright
1996 - 2022
Webmaster:
Kirt Blattenberger,
 BSEE - KB3UON

RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The Internet was still largely an unknown entity at the time and not much was available in the form of WYSIWYG ...

All trademarks, copyrights, patents, and other rights of ownership to images and text used on the RF Cafe website are hereby acknowledged.

My Hobby Website:
 AirplanesAndRockets.com

Try Using SEARCH
to Find What You Need. 
There are 1,000s of Pages Indexed on RF Cafe !

height-line