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b4bb4ge
Joined: 28 Feb 2008
Posts: 100
Helped: 15
Location: Colorado, USA
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 05 Nov 2009 18:30 Error Vector Magnitude Questions |
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Hi all,
I am looking to gain information on EVM specs and how one measures EVM (I know the power definition) but what equiptment is use and what does it does it do that a PNA can not do?
What amplifiers are better for which EVM specs (ie GaAn or GaAs for example). Does anyone know any good papers or books on such subjects?
With GaAs the EVM usually gets better (device gets more linear) as one gets further and further away from the compression point, is this also true with GaAn devices?
Is EVM all about the linearity of the device?
Thanks all,
Babbage
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vfone
Joined: 10 Oct 2001
Posts: 2327
Helped: 327
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05 Nov 2009 21:17 Re: Error Vector Magnitude Questions |
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A good device to measure the EVM is the VSA (Vector Signal Analyzer)
http://www.home.agilent.com/upload/cmc_upload/LeeWLAN64QAM-800x623.jpg
Also some Spectrum Analyzers have EVM test option incorporated.
PNA is a Network Analyzer and this cannot measure EVM, intermods, or modulation spectrum.
The only linearity test that PNA can do indirectly is P1dB (compression point). Change the input level into DUT and check the compression gain at the output.
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biff44
Joined: 24 Dec 2004
Posts: 1835
Helped: 244
Location: New England, USA
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05 Nov 2009 23:51 Re: Error Vector Magnitude Questions |
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Some obvious causes of EVM, such as AM to AM, or AM to PM conversion, can be measured statically with a network analyzer. In your case, measuring GaAs or GaN amplifiers can be done statically.
Other sources of EVM error, such as a switched DC power supply not turning on in time, momentary instabilities, multitone generation of in-band products, etc. can only be measured dynamically with a vector signal analyzer.
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