Proposed 8gfc specs for emi reduction
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Proposed 8GFC Specs for EMI Reduction. Mike Jenkins LSI Logic. Proposed Modified or Additional Specifications to Control EMI. Differential to Common Mode Conversion (SCD11 & SCD22) Constrains CM voltage generated from differential signal Similar to “Impedance Balance” in SATA spec

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Proposed 8GFC Specs for EMI Reduction

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Proposed 8gfc specs for emi reduction

Proposed 8GFC Specsfor EMI Reduction

Mike Jenkins

LSI Logic


Proposed modified or additional specifications to control emi

Proposed Modified or Additional Specifications to Control EMI

  • Differential to Common Mode Conversion (SCD11 & SCD22)

    • Constrains CM voltage generated from differential signal

    • Similar to “Impedance Balance” in SATA spec

  • TX Common Mode Voltage

    • Convert from single RMS or peak voltage to a limit across frequency spectrum

  • See http://www.t10.org/ftp/t10/document.07/07-007r2.pdffor same specs as adopted by 6 Gb/s SAS

T11/07-436v0


Proposed format of specs

Proposed Format of Specs

Measured Value < max [ L, min [ H, N + 13.3 log10(F/4.25GHz) ] ]

50 MHz < F < 8.5 GHz

H: Max value (high

frequency asymptote)

H

N: Value at Nyquist

frequency (4.25 GHz)

N

L

L: Min value (low

frequency asymptote)

T11/07-436v0


Fcc radiated emissions limits relative to 1uv meter

FCC Radiated Emissions Limits(relative to 1uV/meter)

Mechanism for converting common mode noise into EMI is unknown, but EMI is assumed to be proportional to the noise that causes it.

Hence, limit curve for each parameter (in dB) should reasonably track these Radiated Emission limits.

T11/07-436v0


Proposed tx cm voltage limit l 12 7 dbmv rms n 28 dbmv rms

Proposed TX CM Voltage Limit ( L = 12.7 dBmV(rms), N = 28 dBmV(rms) )

T11/07-436v0


S parameter single ended to mixed mode conversion

S-parameter Single-ended to Mixed Mode Conversion

Note: S13 = S31 (reciprocal), so

SDC11 = SCD11 = (S11–S33)/2

SDD11

SDC11

1

Smm =

2

SCD11

SCC11

For derivation of conversion to mixed mode parameters, see (for example):

http://www.simtech.a-star.edu.sg/Research/TechnicalReports/TR04JT03.pdf

T11/07-436v0


Proposed scd11 scd22 limit l 26db n 10 7db

Proposed SCD11, SCD22 Limit(L = -26dB, N = -10.7dB)

+Input

(port 1)

CP

RP

delay

skew

-Input

(port 2)

Cn

Rn

RP = Zo x (1+TOLP)

Rn = Zo x (1+TOLn)

Additional skew added to +Input

T11/07-436v0


A note about impedance scaling in mixed mode conversion

A Note about Impedance Scaling in Mixed Mode Conversion

For scattering parameters, the incident & reflected ‘power waves’

are defined as V+/sqrt(Zref+) and V-/sqrt(Zref-), respectively, where Zref+ is the reference impedance of the incident wave and Zref- is the reference impedance of the reflected wave.

In mixed mode parameters, these impedances can be different. Hence, a differential input voltage of 1200mVpp encountering the proposed limit SCD11 of -10.7dB = 0.292 at the Nyquist frequency results in a reflected common mode voltage of:

Vcm = 1200mVpp x 0.292 x sqrt[25W/100W] = 175.2mVpp.

This limit compares reasonably with the proposed +28dBmV(rms) common mode TX voltage limit, equivalent to 25mV(rms) = 70.7mVpp.

ref: http://en.wikipedia.org/wiki/S-parameters

T11/07-436v0


Summary

Summary

  • A spec format is proposed to limit AC common mode voltage in 800-DF-EL-S

    • Spectral limit line

    • Limits single-tone 4.25GHz Vcm to 25mV(rms)

  • Limits for SCD11 & SCD22 also proposed to control EMI

T11/07-436v0


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