Two large frequencies with a small offset

Thread Starter

kender

Joined Jan 17, 2007
264
Colleagues,

In my circuit I need 2 frequencies: f1 and f1+f2. f1 = 40MHz with some inevitable but acceptable clock drift. f2 = 10kHz approximately. Square waves at digital levels are OK. What are good ways to obtain such frequencies?

Thanks,
Nick
 

Papabravo

Joined Feb 24, 2006
13,565
Colleagues,

In my circuit I need 2 frequencies: f1 and f1+f2. f1 = 40MHz with some inevitable but acceptable clock drift. f2 = 10kHz approximately. Square waves at digital levels are OK. What are good ways to obtain such frequencies?

Thanks,
Nick
I don't understand the meaning of "Square wave at digital levels are OK". Do you want square waves or don't you? It is hardly ever a good idea to be equivocal about your requirements.

Using a doubly balanced mixer followed by a sharp passive high-pass filter to remove the (f1-f2) component is a possibility but only if we can use sine waves.

If it must be square waves then I would suggest a 13.33 MHz crystal oscillator in 3rd overtone mode(which when viewed on a scope will resemble a sine wave anyway), and a phase locked loop with a 10 kHz reference and a divisor of 4001 to get 40.01 MHz.

How about two identical phase locked VCO's one with a divisor of 4000 and the other with a divisor of 4001. Both could use the same 10 kHz reference.

What do you want to do with them anyway?
 
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