andriclt
Newbie level 3
Hi,
I have a couple of questions regarding the design of DSMs in Frac-N PLLs
I am trying to design 3rd order single loop DSMs with 3-5 level Quantizer outputs. How do I determine the DSM filter coefficients so that I am able to use a 2bit Quantizer in it and ensure stability? With a classical 3rd order SDM with NTF = (1-z-1)3, if I reduce the number of Quantizer levels below 7, I am saturating the accumulators and the DSM goes unstable.
I have read literature in the past that talks about moving the poles from the origin and/or adding zeros to improve stability, but I am unable to recollect where I read them. Any pointers to design methods and stability analysis of DSM will be great.
Secondly, I am confused about what the scale factor should be to refer the DSM noise to the input of PFD as phase noise. Michael Perott's thesis used to have it, but ever since he left MIT, they have brought down his research material with it.
Much appreciated,
andriclt
I have a couple of questions regarding the design of DSMs in Frac-N PLLs
I am trying to design 3rd order single loop DSMs with 3-5 level Quantizer outputs. How do I determine the DSM filter coefficients so that I am able to use a 2bit Quantizer in it and ensure stability? With a classical 3rd order SDM with NTF = (1-z-1)3, if I reduce the number of Quantizer levels below 7, I am saturating the accumulators and the DSM goes unstable.
I have read literature in the past that talks about moving the poles from the origin and/or adding zeros to improve stability, but I am unable to recollect where I read them. Any pointers to design methods and stability analysis of DSM will be great.
Secondly, I am confused about what the scale factor should be to refer the DSM noise to the input of PFD as phase noise. Michael Perott's thesis used to have it, but ever since he left MIT, they have brought down his research material with it.
Much appreciated,
andriclt
