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Connection between IP3 and P1dB... - RF Cafe Forums
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System Designer |
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Post subject: Connection between IP3 and P1dB...
Posted: Sun Sep 25, 2005 2:20 pm
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Hello everyone,
Help needed:
What
is the connection between IP3 and 1dB compression
point in RF Amplifiers ? as I understood, when I
deal with Amp. with high IP3 (for example: +30dBm)
there is a problem to measure it with spectrum analyzer...
And I don't know what's the answer ?
I assume that for seeing the IP3 spurious, I need
to inject very high power signal which might compress
the Amp.
but I can't figure other way for measure
the IP3 power without injecting very high signal
and compressing the Amp. ??!!
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IR |
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Post subject:
Posted: Mon Sep 26, 2005 8:13 am
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Joined: Mon Jun 27, 2005
2:02 pm
Posts: 413
Location: Germany
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Hello,
There is no constant connection between
IP3 and P1dB in amplifiers, and even the "rule of
thumb" of: IP3=P1dB+10dB
is not accurate
and doesn't apply. These quantities are dependent
by the technology and process of the amplifier.
However, you can say that in amplifiers the IP3
is always higher than P1dB.
To measure the
IP3 you need to inject 2 signals that are adjacent
to each other, and measure the 3rd orfer products.
The formula to measure the IP3 is:
OIP3=P1+IMR3/2
Where:
P1 - The output power of the fundamental
signal
IMR3- The power difference between third
order products to fundamental product [dBc].
The IEEE definition is that the IMR3 should
be equal or higher than 20dBc: IMR3 >=20dBc
In linear operation, if you increase the input
signals by 1dB, the third order products will increase
by 3dB. You should do the IP3 measurement in small
signal (That is being covered by the IEEE definition)
to obtain an accurate result.
_________________
Best regards,
-
IR
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New System Designer |
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Post subject:
Posted: Wed Sep 28, 2005 3:59 pm
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IR |
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Post subject:
Posted: Thu Sep 29, 2005 2:12 pm
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Joined: Mon Jun 27, 2005
2:02 pm
Posts: 413
Location: Germany
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You are welcome!
One more clarification:
Quote:
to measure the IP3 you need to inject 2 signals
that are adjacent to each other
According to the IEEE the IP3 measurement
is done under a narrwband condition, which is: ±5%
of the center frequency. That gives you the range
in which the adjacent signals can be located.
Good luck!
_________________
Best regards,
-
IR
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Posted 11/12/2012
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