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P1dB definition - RF Cafe Forums

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

Post subject: P1dB definition Posted: Mon May 18, 2009 9:31 am


Joined: Wed Aug 16, 2006 8:20 am
Posts: 23
Location: India
In the data-sheets the P1dB for an amplifier or mixer is defined for at single frequencies. Take the case of a UWB signal of say 500 MHz bandwidth centered at an LO signal of 4.9 GHz where have a power distribution such that all frequencies component from 4.65 GHz to 5.15 GHz have same amplitude level. Consider that the amplitude levels are just below the P1dB rating at the respective frequencies for a given amplifier.
my question is

1. Will the device saturate?
2. If yes then how do we find the maximum power that can be applied to the device input before it reaches saturation in the presence of such a signal?

Ashish Bondia,
Design Engineer- RF


Post subject: Re: P1dB definitionPosted: Mon May 18, 2009 8:23 pm

Site Admin

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

P1dB by definition is frequency selective, that means it is defined only per single frequency. If you want to know the P1dB characterstic of your amplifier for a wide band of frequencies, you have to measure it for each frequency.

If your BW is very wide, you can measure the P1dB for small frequency spacings and assuming that the device's flatness is relatively small, you can interpolate the P1dB for the frequencies in between.

saturation occurs after P1dB has been reached.

There is a term called back off, which is defined as

Backoff= P1dB(in)-Pin(actual)


P1dB(in) - is the P1dB level at the input (measured).
Pin(actual) - actual provided input power.

If the backoff which you get is positive, then you are away from P1dB and therefore far from saturation.

Best regards,

- IR


Post subject: Re: P1dB definitionPosted: Tue May 19, 2009 10:56 am


Joined: Thu Sep 25, 2003 1:19 am
Posts: 50
Location: texarcana
Is it possble to add the tone power to LOG(N).?

N= number of channels

Posted  11/12/2012
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