# 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 AAC Fanatic!

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
3,384
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If this is what you're referring to:

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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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
2
Yes thats it with the dotted line.

9. ### Tony Elliott Thread Starter Member

May 8, 2015
140
2
Thank you for these notes, just having a good read of the info.

10. ### Tony Elliott Thread Starter Member

May 8, 2015
140
2

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.