P1 dB - RF Cafe Forums

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

satish.1979
Post subject: P1 dB Posted: Wed Nov 29, 2006 3:01 am

Captain

Joined: Tue Oct 03, 2006 3:03 am
Posts: 11
Location: India
What is the need and significance of P1 dB point in the amplifier design

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IR
Post subject: Posted: Wed Nov 29, 2006 7:48 am

Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany
P1dB gives an indication of the output power to which the amplifier is capable to deliver before going into saturation.

Before the amplifier reaches the P1dB it behaves linearly that means a linear relation between its input power and output power. So if you increase the input power by 1dB the output power will increase in 1dB as well.

The amplifier doesn't enter sharply into the P1dB area. The output power becomes non-linear before this point reaches. The gain will decrease gradually from the linear gain G (Measured in small signal) to G-1dB. This can be seen if you increase the input power dB by dB until you will reach the G-1dB point in which the output power will be the P1dB [dBm]

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- IR

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Augusto
Post subject: Posted: Wed Nov 29, 2006 6:03 pm

Lieutenant

Joined: Wed Nov 29, 2006 5:51 pm
Posts: 2
Actually the more precise definition is the power at which the power response deviates from the linear response by 1 dB.

In other words for instance when you have an amplfier that has a gain of say 10 db you will see a difference between output power and input power of 10 dB in the linear region. As you increase the input power there is a point where the power amplifier starts saturating and the power increases to a point that is less than the 10dB gain expected. In this particular case of 10dB gain the output power at which the power gain is 9dB instead of the expected 10dB is called the "1dB compression point".

Being that the 1dB compression is already deviated from the linear response starting when it starts to compress this area is not really useful for linear transmission. In most cases for acceptable performance you need to back away from this point by 6 to 12 dB.

In most spread spectrum system when using non-linearized amplifiers you usually use the 10dB backoff rule of thumb to get acceptable spectral performance.

Augusto.

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satish.1979
Post subject: Why not P2/P3 dB?Posted: Wed Jan 03, 2007 11:48 pm

Captain

Joined: Tue Oct 03, 2006 3:03 am
Posts: 11
Location: India
Why not P2/P3 dB?

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IR
Post subject: Posted: Fri Jan 05, 2007 5:09 pm

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

To the best of my knowledge, it is a matter of industry standard definitions.

You can also choose P2dB, P3dB. Actually there is a use for these figures for quantizing the AM/AM curves of PA in order to generate opposite curves for pre-distortion linearization schemes.

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Best regards,

- IR

Posted  11/12/2012

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