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frequency synthesizer

L

Lost'n Found

Jan 1, 1970
0
Hello,

I was reading about frequency synthesizers and it seems I am missing some
concept.

These synthesizers can generate higher frequency. On the specification
sheets, I read that we can divide the reference frequency by certain
factors. My question is: If we are dividing the frequency, why are we
getting much higher frequencies at the output?
 
T

Tim Wescott

Jan 1, 1970
0
Lost'n Found said:
Hello,

I was reading about frequency synthesizers and it seems I am missing some
concept.

These synthesizers can generate higher frequency. On the specification
sheets, I read that we can divide the reference frequency by certain
factors. My question is: If we are dividing the frequency, why are we
getting much higher frequencies at the output?
A:

You can find out amazing amounts of stuff doing web searches, like on
"frequency synthesizer theory".

B:

You can only get frequencies out that are multiples of the reference
frequency going to the phase detector (unless you're using a fractional
N synthesizer -- You can find out amazing amounts of stuff doing web
searches). It's easier to make a good clock source from a crystal, so
if you want to have a synthesizer work in 5kHz steps you'll want to
generate a clock at (say) 5MHz, divide it by 1000, then synthesize a
frequency from that in 5kHz steps.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google? See http://cfaj.freeshell.org/google/

"Applied Control Theory for Embedded Systems" came out in April.
See details at http://www.wescottdesign.com/actfes/actfes.html
 
R

Rich Grise

Jan 1, 1970
0
Hello,

I was reading about frequency synthesizers and it seems I am missing some
concept.

These synthesizers can generate higher frequency. On the specification
sheets, I read that we can divide the reference frequency by certain
factors. My question is: If we are dividing the frequency, why are we
getting much higher frequencies at the output?

This might be helpful:
http://en.wikipedia.org/wiki/Frequency_synthesiser
That's just one of "about 381,000 for 'frequency synthesizer'" at
http://www.google.com/search?q="frequency+synthesizer"

Have Fun!
Rich
 
A

Andrew Holme

Jan 1, 1970
0
Lost'n Found said:
Hello,

I was reading about frequency synthesizers and it seems I am missing some
concept.

These synthesizers can generate higher frequency. On the specification
sheets, I read that we can divide the reference frequency by certain
factors. My question is: If we are dividing the frequency, why are we
getting much higher frequencies at the output?

Because we divide down and then multiply up. A common reason for doing so
is to reduce the step size / comparison frequency.
 
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