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Design >> RF Design >> Digital Sigma Delta Modulator for Frac N PLL
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Message started by timmc6 on Jul 18^th, 2006, 6:23am

Title: Digital Sigma Delta Modulator for Frac N PLL
Post by timmc6 on Jul 18^th, 2006, 6:23am

Hello,

I am trying to design a Frac N PLL using an all digital ΣΔ modulator. All literature I have found so far refer to the ΣΔ as an ADC or DAC, but it seems to me that the modulator should have a digital input and digital output. Can any help clarify this, and maybe point me to some literature that talks about the design of ΣΔ's used in Frac N PLL's? Thanks.

Tim

Title: Re: Digital Sigma Delta Modulator for Frac N
Post by Aigneryu on Aug 4^th, 2006, 8:32pm

Consider the oversampling ADC theory, and implement it in a "numerical" form.
Just treat the modulator as a numerical type ADC, which means you input a fractional
number in binary format then you get a series of modulated output bit patterns.