Phase Locked Loop Schematic Question

Thread Starter

Tony Elliott

Joined May 8, 2015
155
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
 

Dodgydave

Joined Jun 22, 2012
9,320
Its optional extra, you can use a cd4017 decade counter or other ripple counter, there are other pll chips, CD4046, NE565.
 

ian field

Joined Oct 27, 2012
6,539
You would put a frequency divider chip (binary counter) there, if you wanted to measure frequencies lower than what the LM331 can operate at.
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.
 

Thread Starter

Tony Elliott

Joined May 8, 2015
155
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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