10MHz divide down to 10KHz. Which is the best way?

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neazoi

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Hello,
since frequency division improves frequency stability (CORRECT me if I am wrong)
I am thinking of dividing down a 10MHz TCXO to achieve a 10KHz square signal with excessive stability.

What is the best way to do it?
One way is using a micro (code attached)
Another way is using 74AC74 chips for the division.

Which way should I prefer for more accuracy?
 

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I wouldn’t call it stability, but accuracy.
Each division by 10 moves the accuracy by 0.1.

BTW. 7474 has 2xD FFs, and each can only divide an input by 2.
To divide by ten you need something like 7490, and to ensure the 50% output you may first divide the input by 5 and then by 2.
But I prefer the software solution that you’ve suggested …
:wink:
IanP
 
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    neazoi

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Frequency stability is not changed by division. If you had 10ppm stability at 10MHz you will have 10ppm stability at 10kHz after division.

Keith
 
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    neazoi

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Ok, I have found a decade divider circuit that uses 74ACxxx quad flip flops and divides down to 100khz, 10khz and 1hz. I do not have the circuit in this computer I work now, but if interested I can post it.
Obviously, in my previous post I was confused about stability and accuracy.

That I mean is that an oscillator that drifts 10hz upwards on 10mhz would drift 5hz upwards when divided down to 5mhz.
Is that the case?

If so, I am thinking of using a pll (which accepts a 10khz reference input) to lock to another 10mhz oscillator, to improve it's stability
 

you might well use three nos of 74HC90 to get divide by 10/10/10 it becomes 10KHz.
Otherwise you can also use two chips of 74HC390 each having dual divide by 10
thus use three sections in tandem to get division by 1000 and result would be 10KHz square wave.

depends on the need. if it is a school exercise, they might be intending experience of gates and division.
I expect 74HC4040 and external 10.245 MHz crystal oscillator, shall give you 10.004KHz at its /10 output, which close to 10KHz. These crystals are generally used in cordless phones etc
 
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