how to design a dual-modulus divider in ADS 2009?

[analog_member]

Hi all!!

I'm designing a fractional-N frequency synthesizer in ADS. I have designed the VCO , and i want to design a dual-modulus divider for dividing the VCO's output. I do not want to use the already available VCO divide-by-N block present in ADS as then i cant make use of my designed VCO. Plz help me . Any readymade block or design procedure for it will help. It's urgent.

Thank u all

 

[erikl]

Can't you simply replace the VCO from the already available VCO divide-by-N block by your VCO?

Sorry, I know neither the construction of this block nor the ADS 2009 design system.

 

[analog_member]

that is what I'm doing, I'm replacing the VCO divide-by-N block present in ADS by my VCO, but i need to design a dual-modulus divider to divide the VCO frequency, as a fractional-N frequency synthesizer requires a frequency divider after the VCO.

 

[erikl]

that is what I'm doing, I'm replacing the VCO divide-by-N block present in ADS by my VCO, but i need to design a dual-modulus divider to divide the VCO frequency, as a fractional-N frequency synthesizer requires a frequency divider after the VCO.

Any frequency synthesizer requires a frequency divider after the VCO, I'd think.
Can't you - additionally - replace the original divide-by-N block by your fractional-N-divider block?

May be this seems to be a dumb question, too, but many of us (potential helpers) don't know in which type the original ADS frequency synthesizer is available. Schematics, functional, behavioural or high level language description? I'd think such a replacement should be possible in any of these presentation forms.

And we even don't have a block circuit of the original and your intended solution.

 

[dick_freebird]

You need a dual modulus prescaler if you intend to cover
a wide range of frequencies finely. If you are making a
fixed frequency / fixed ratio PLL, you don't need the
dual modulus - you just need a modulus that is a factor
of the divisor. And a large enough factor, that it makes
the CMOS counters able to run at the remaining frequency
without being so challenged that phase noise suffers.

Look up "pulse swallowing" as the common method for
getting a dual modulus like 5/6 or 10/11. If you indeed
need it.