Post subject: P1 dB Posted: Wed Nov 29, 2006 3:01
Joined: Tue Oct 03, 2006 3:03 am
What is the need and significance of P1
dB point in the amplifier design
subject: Posted: Wed Nov 29, 2006 7:48 am
Joined: Mon Jun 27, 2005 2:02 pm
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]
subject: Posted: Wed Nov 29, 2006 6:03 pm
Joined: Wed Nov 29, 2006 5:51 pm
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
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.
Post subject: Why not P2/P3
dB?Posted: Wed Jan 03, 2007 11:48 pm
Tue Oct 03, 2006 3:03 am
not P2/P3 dB?
Post subject: Posted:
Fri Jan 05, 2007 5:09 pm
Jun 27, 2005 2:02 pm
To the best of my knowledge, it is a matter of industry standard
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