Basic Frequency SynthesizerQuestion

[Sommes]

If I put a SN7490(divided by five) IC in a Frequency Synthesizer PLL
cirucit. Is it equal to input frequency * 5?

Cheers

 

[Fred Bloggs]

Sommes wrote:

If I put a SN7490(divided by five) IC in a Frequency Synthesizer PLL
cirucit. Is it equal to input frequency * 5?

Cheers

The PLL synchronizes phase. A frequency divider is a phase attenuator.
The divider causes the PLL to neutralize phase difference between the
input signal and the phase attenuated output in much the same way an op
amp neutralizes the difference between between input signal and
attenuated output. In both cases, the "gain" is the reciprocal of the
feedback attenuation. The reciprocal of 1/5 is 5, so the PLL output
frequency will be 5x the input frequency.

 

[Ken Smith]

In article <418500BF.7090900@nospam.com>,
Fred Bloggs <nospam@nospam.com> wrote:
[...]

The PLL synchronizes phase. A frequency divider is a phase attenuator.
The divider causes the PLL to neutralize phase difference between the
input signal and the phase attenuated output in much the same way an op
[.. correct stuff snipped ..]

Fred forgot to add "This assumes the PLL is locked". If you use the XOR
type phase detector, you can get locking to harmonics and subharmonics
etc. Most of the flip-flop detectors don't have this problem.

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