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PAR vs. EVM - RF Cafe Forums
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Post subject: PAR vs. EVM
Posted: Fri Feb 19, 2010 4:35 pm
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Joined: Mon May 04, 2009
6:47 pm
Posts: 22 |
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Confused!!!
I'm designing a 1W OFDM power
amplifier for 500~700MHz. The signal PAR is about
12.5dB and ESG reading is about the same, which
means the PA P1dB should be better than (30+12.5)
= 42.5dBm. In my design P1dB rolls off to 38.5dBmat
each end, which is 4dB compressed, however EVM measurement
is better than -39dB.
Can someone help me
understand this? Could a compressed PA provide doog
EVM?
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IR |
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Post subject: Re: PAR vs. EVM
Posted: Wed Feb 24, 2010 4:03 pm
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| Site Admin |
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Joined: Mon Jun 27, 2005
2:02 pm
Posts: 373
Location: Germany
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Usually the EVM can not be good if the P1dB is lower
than the signal's PEP.
Maybe it has to do
with the filter the signal has (Raised-Cosine etc),
and other signal parameters like clipping which
affect the CCDF. This can affect (improve or degrade)
the EVM.
But this is just my guess...
_________________
Best regards,
-
IR
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RDO-RF |
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Post subject: Re: PAR vs. EVM
Posted: Mon Mar 01, 2010 2:43 pm
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Joined: Wed Apr 08, 2009
7:53 am
Posts: 12 |
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The signal has 12.5dB of PAR, but that doesn't exactly
means that your power amplifier should have the
same back-off. Note that in the CCDF curve the 12.5dB
peaks have very low probability. Remember that EVM
is an average value and perhaps your can effort
clipping the signal once a while having no grater
effect on EVM.
For some signals, clipping affects
first the ACPR and then the EVM. You can check this
on your VSA, by looking if this good EVM output
signal that you have has degradation on its ACPR.
This was my guess.
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Posted 11/12/2012
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