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What sets the phase-noise spec in RF transmitters? (Read 195 times)
weber8722
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What sets the phase-noise spec in RF transmitters?
Nov 18th, 2011, 1:23am
 
Hi, I am more familiar with receivers, and there phase-noise is extremely important for blocker performance. However, why phase-noise is important for typical RF mobile station transmitters? What it is impacting most? For standards like GSM, WLAN, EDGE, etc. Huh

Bye Stephan
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raja.cedt
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Re: What sets the phase-noise spec in RF transmitters?
Reply #1 - Nov 18th, 2011, 2:55am
 
hello,
In transmitters local oscillator noise is amplified by the subsequent amplifier stages and is eventually fed to the antenna together with the wanted signal. The wanted signal is therefore surrounded by a band of noise originating from the phase noise of the local oscillator

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loose-electron
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Re: What sets the phase-noise spec in RF transmitters?
Reply #2 - Nov 21st, 2011, 2:25pm
 
Out of band spectral spreading?

Essentially keeping the transmitter in its channel would be my guess here.
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RFICDUDE
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Re: What sets the phase-noise spec in RF transmitters?
Reply #3 - Nov 25th, 2011, 5:04pm
 
Probably EVM.
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rfcooltools.com
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Re: What sets the phase-noise spec in RF transmitters?
Reply #4 - Jan 10th, 2012, 10:02pm
 
weber8722,

All answers so far are correct,
For mobile devices the transmit being at max is correlated with receiver seeing min power ie rx is near the thermal noise floor . In a full duplex (transmit and receive operating simultaneously) TX phase noise out of band directly increases the noise at the receiver input minus filtering if any. For low lower order modulation bpsk qpsk phase noise is less of a concern in band for tx.  But for higher order modulation such as QAM then the system budget for in band phase noise is stricter since the constellation can be degraded (ie EVM) at the time of transmit.  In wire line communications the transmit can degrade other receivers on the same line.  

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