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Altera_Forum's avatar
Altera_Forum
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13 years ago

Stratix V PLL question

Hello.

I am beginning to study Stratix V.

My question concerns fPLLs of these ICs.

Datasheet for Stratix V says:

fractional plls may be

individually configured for integer mode or fractional mode with third-order

delta-sigma modulation.

"Clock Networks and PLLs in Stratix V Devices" chapter has a picture of the PLL' structure that contains Delta Sigma Modulator on it.

But there is no more information about this delta sigma modulator in any documentation.

Can somebody say, what is the delta sigma modulator in Stratix V, and how has it to be used?

any theoretical or practical information is required.

4 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    13 years ago

    i've found that the fractional PLLs are basically done entirely behind the scenes. basically you put in the Reference Clock Frequency and the Desired Frequency, then select the Actual Frequency that best matches from the selection. that's it

    in the Fitter Report you can see what fPLL settings are actually being used
  • Altera_Forum's avatar
    Altera_Forum
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    13 years ago

    From this article: http://www.altera.com/devices/fpga/stratix-fpgas/stratix-v/overview/fpll/stxv-fpll.html?gsa_pos=2&wt.oss_r=1&wt.oss=delta sigma

    as shown in figure 2, the client frequency information in the aggregate data stream is used to control the delta-sigma modulators in the fplls, allowing for precise synthesis of the required client line rate frequencies.

    So, we should give to fPLL some information, that is used by delta-sigma modulators to generate required frequency.

    The question is, what information should we give and how it will be used to produce frequency that we need and what will be the quality of the clock.
  • Altera_Forum's avatar
    Altera_Forum
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    13 years ago

    I assume you've got your question answered. You just put in your desired input and output clock frequencies and tell the altera_pll wizard to use fractional mode.

  • Altera_Forum's avatar
    Altera_Forum
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    13 years ago

    Can anyone comment on the performance of integer vs fractional mode?