different clock signal needed

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jayguarprince

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Hi all,

I need to generate two different clock signals (10MHz/25MHz square wave 50% pulse width) 1.8V level on a single PCB board. I have thought of using programmable PLL ICs with external crystal but problem is I am not allowed to use any kind of digital programming (such as uC). Couldn't find any suitable chips on the market which the output frequency is set by using external passive components (resistors, capacitors etc.).

Anyone can help me on this?

Thanks.
Doug
 

jayguarprince,

You could use a 50M crystal and run it through some simple logic. A divide by 2, a Flip Flop, will produce the 25M. A counter that counts to 5 will produce the 10M clock.

Sckoarn
 

A counter that counts to 5 will produce the 10M clock.
Click to expand...
It has either to act on both clock edges or use additional logic to get 50% duty cycle from a 50 MHz input.
 

As FvM states, logic would have to be able to use both edges, and that is not the easyest way.

If you can use a 100 MHz crystal, you can use a divide by 4 logic to get 25 MHz and a divide by 10 to get the 10MHz. This way you can use all positive edge logic to do your divide.
 

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