Looking for PPL which receives 74 Mhz

Help on PLL

Hi everybody,

I need to know if it's possible to find a PLL which receives 74 MHz signal
and the output is ~4MHz so that the ratio is 74 MHz * 4096/74250 = 4.08 MHz.

Is it possible? does anyone knows such component?

Thanks,

Re: Help on PLL

I think that imposible. the fraction_N PLL can not do that. Maybe you can use DDS to do it.

Help on PLL

Dual modulus PLL works always in this case..

Ntotal=( Main Divider-1) 2^n+(P+2^n)

P: Programmed values
Main Divider= Main divider Programmed values

So, it's always possible obtain rational values with dual mudlus or swallow controlled PLL

Re: Help on PLL

Are you familiar with such component? can you give me datasheet or part number for it?

Thanks,

Re: Help on PLL

ericz said:

Are you familiar with such component? can you give me datasheet or part number for it?

Thanks,

Click to expand...

https://www.fujitsu.com/downloads/MICRO/fme/pll/e421349.pdf

Look at that datasheet ( for instance, you may findyourself many.. ).
In this data sheet the formulae is defined as

fVCO = [(M x N) + A] x fOSC ¸ R (A < N)

Here,

fVCO : Output frequency of external voltage controlled oscillator (VCO)
N : Preset divide ratio of binary 12-bit programmable counter (5 to 4,095)
A : Preset divide ratio of binary 6-bit swallow counter (0 to 63)
fOSC : Output frequency of the reference frequency oscillator
R : Preset divide ratio of binary 14-bit programmable reference counter (5 to 16,383)
M : Preset modulus of dual modulus prescaler (64)

For example. Let your frequency to be synthesized is 74MHz and reference frequency ( at the same time channel spacing ) is 15kHz. If you programme R value as ( for instance ) 512, cyrstal frequency will be 7.68MHz.

R=7.68MHz/15kHz=512
( there will be many possibilities to use different cyristal values))

In that case comparison frequency will be 15kHz and Total division ratio will be
NT= 74MHz/15kHz=4933.333. But this will be exact value of 15kHz so VCO frequency should be 73.995 MHz.

So ,main task is to realize that value.

So, [(M x N) + A]=4933. Since M value is 64 that is constant,

So finally , by taking integer value of N ( 4933/64=77.07813 -->>77 )we find,

N=77
M=64
A=5

values.

I hope that's clear..