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Design >> RF Design >> Rough Estimation of EVM
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Message started by pancho_hideboo on Oct 12^th, 2005, 12:42am

Title: Rough Estimation of EVM
Post by pancho_hideboo on Oct 12^th, 2005, 12:42am

Hi.

In Transmitter design, various issues could cause EVM(Error Vector Magnitude) degradation.

For quadrature modulator, we can consider two issues roughly.

(1) Linear issues such as carrier leakage, incomplete sideband suppression, Phase Noise and group delay ripple, etc.

(2) Nonlinear issues such as AM/AM, AM/PM, PM/PM, PM/AM.

So it is useful to relate carrier leakage, sideband suppression, phase noise, group delay ripple, P1dB, IP3 and IP5, etc. to EVM for rough estimation of EVM.

Of course, EVM is intensively dependent on modulation scheme, peak factor,
power level, backoff, etc.
So it is very difficult to estimate EVM.
Nevertheless we still need rough estimation of EVM.

Does anyone know good relationship between EVM and primitive parameters ?

???

Title: Re: Rough Estimation of EVM
Post by Eugene on Oct 12^th, 2005, 10:08am

EVM can easily be related to phase noise (pn)and sideband rejection (sbr).

EVM(pn) = rms pn in radians.

EVM(sbr) = sbr (in a fraction).

Combined, we usually assume the total EVM is just the root-sum-squared combination of the two individual EVMS:

EVM(pn and sbr) = sqrt[EVM(pn)**2+EVM(sbr)**2].

In general, we do the same thing for all sources of EVM.

To relate EVM to nonlinear impairments, or other impairments which are not easy to analyze, I believe most engineers use simulation to empirically derive relationships between EVM and the various impairments. The relationships of course depend on modulation. I hope this helps.