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Proposed 8GFC Specs for EMI Reduction

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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  1. Proposed 8GFC Specsfor EMI Reduction Mike Jenkins LSI Logic

  2. 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

  3. 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

  4. 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

  5. Proposed TX CM Voltage Limit ( L = 12.7 dBmV(rms), N = 28 dBmV(rms) ) T11/07-436v0

  6. 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

  7. 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

  8. 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

  9. 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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