Phase Locked Loop Schematic Question

Discussion in 'General Electronics Chat' started by Tony Elliott, Feb 20, 2016.

  1. Tony Elliott

    Thread Starter Member

    May 8, 2015
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    pg: 8 fig: 13
    http://www.ti.com/lit/an/snoa593b/snoa593b.pdf

    I have been looking to build this circuit and on the schematic I looked at the optional (+N frequency to voltage divider), can anyone tell me what this is? And as it is optional what is its function as I want to use the circuit to convert frequency to voltage with a presition response time.

    Anthony
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Its optional extra, you can use a cd4017 decade counter or other ripple counter, there are other pll chips, CD4046, NE565.
     
  3. dl324

    Distinguished Member

    Mar 30, 2015
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    If this is what you're referring to:
    upload_2016-2-20_11-18-10.png
    The optional counter is used to lock on a multiple of the input frequency.
     
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  4. Lestraveled

    Well-Known Member

    May 19, 2014
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    You would put a frequency divider chip (binary counter) there, if you wanted to measure frequencies lower than what the LM331 can operate at.
     
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  5. ian field

    Distinguished Member

    Oct 27, 2012
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    The 331 is equivalent to the Raytheon RC4151 - that may open up the search to a bigger resource of appnotes.

    When a PLL is used for frequency conversion - a divider is used to put a divided down frequency on the phase comparator so the VCO has to go faster to keep up. That's the classic textbook example of using a divider to multiply frequency.
     
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  6. bertus

    Administrator

    Apr 5, 2008
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  7. Lestraveled

    Well-Known Member

    May 19, 2014
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    Remember, this is a PLL precision frequency to voltage converter. The "F input" is the frequency to be measured.
     
  8. Tony Elliott

    Thread Starter Member

    May 8, 2015
    140
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    Yes thats it with the dotted line.
     
  9. Tony Elliott

    Thread Starter Member

    May 8, 2015
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    Thank you for these notes, just having a good read of the info.
     
  10. Tony Elliott

    Thread Starter Member

    May 8, 2015
    140
    2
    20394934Y-0.GIF
    So this can be used to translate the vco's frequency (with optionional outputs from s1 to s10 on the 4017) to the readable frequency limit of the lm311.

    And I noticed fig 14 (pg9) on the original schematic improves frequency range.
     
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