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delta sigma simulation, MATLAB vs. Verilog A

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jowong1

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matlab delta sigma

I have a confusion involves the SNR comparison of DSM simulated in MATLAB and VA. In MATLAB, I can get the theoretical maximum SNR (88dB) using transfer function blocks and quantizer block. But in VA, it gave me 68dB (I used the laplace transfer function in VA to create my loop filters, and quantizers and DAC are 16 levels). I don't understand why they don't match since I don't have any non-idealities in my VA models.

Thanks
 

delta sigma verilog

Maybe simulation settings like reltol, abstol ,etc
 

matlab verilog

how is it possible that those settings are enuf to chop 20dB off!?!?

Thanks
 

function sigma matlab

matlab is better and it has toolsbox
 

matlab verilog a

ya but i wanna model some non-idealities which MATLAB cannot do......
 

delta-sigma verilog

you can model non-idealities like clock jitters and limited opamp gain using SDToolbox

**broken link removed**
 

sigma in matlab

Matlab error is simple 64bit IEEE-754 numeric. If you use some functions in matlab the error control is "eps"

type eps=2.22e-16

That is typical much tighther than what simulator implement. But set reltol to eps of matlab could fail because most spice relevant models are calculated in 64bit floating point but sometimes with hard coded accuracy or the numerical presiscion is lost by some orders by the implicite routines. So failure in convergence is the result.
 

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