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поискавой системы для электроныых деталей |
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поискавой системы для электроныых деталей |
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ICS841484I датащи(PDF) 13 Page - Renesas Technology Corp |
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ICS841484I датащи(HTML) 13 Page - Renesas Technology Corp |
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13 / 28 page  ICS841484I Data Sheet FEMTOCLOCK® CRYSTAL-TO-0.7V DIFFERENTIAL HCSL CLOCK GENERATOR ICS841484DKI REVISION A NOVEMBER 7, 2012 13 ©2012 Integrated Device Technology, Inc. Spread Spectrum Spread-spectrum clocking is a frequency modulation technique for EMI reduction. When spread-spectrum is enabled, a 32kHz triangle waveform is used with 0.5% down-spread (+0.0% / -0.5%) from the nominal output frequency. An example of a triangle frequency modulation profile is shown in Figure 1A below. The ramp profile can be expressed as: Fnom = Nominal Clock Frequency in Spread Off mode (200MHz with 25MHz IN) Fm = Nominal Modulation Frequency (32kHz) = Modulation Factor (0.5% down spread) (1 – ) Fnom + 2 fm x x Fnom x t when 0 < t < 1 2fm (1 – ) Fnom + 2 fm x x Fnom x t when 1 < t < 1 2fm fm An example of the amount of down spread relative to the nominal clock frequency can be seen in the frequency domain, as shown in Figure 1B. The ratio of this width to the fundamental frequency is typically 0.5%. The resulting spectral reduction is typically 10dB, as shown in Figure 1B. It is important to note the ICS841484 10dB typical spectral reduction is the component-specific EMI reduction, and will not necessarily be the same as the system EMI reduction. Figure 1A. Triangle Frequency Modulation Figure 1B. 200MHz Clock Output In Frequency Domain (A) Spread-Spectrum OFF (B) Spread-Spectrum ON ➤ 1/fm 0.5/fm Fnom (1 - δ) Fnom Time B A – 10 dBm = 0.5% |
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