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A simple problem about sigma delta modulator!

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batmanliufan

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What about the relationship between the input signal range and the the saturation
levels of the op-amp used?
I have read some papers about sd modulator.but they just care about the gain slewrate GBW and so on.
 

Increase input amplitude may cause stability problems. When input signal swing increase, the opamp output swing may also increase,which cause
satuation problem. This may not cause stability problem, but will bring harmonics.
scale the dsm coefficients carefully, make sure that
the opamp output swing will not exceed about 80~90% of the reference voltage.
 

Thank you very much Mr.swicap for your help again!
Now I use simulink to get the parameters of SD modulator.But there are some probles come out when I wrote the matlab files.
I ever think that the saturation voltage of integrator is the input singnal range and the
+-Vref from the 1bit DAC is half of the opamp output swing.

Added after 33 minutes:

Amax=1.35; Op-amp saturation value [V]
how can i get the Amax and +-Vref when the circuits work under 5v vdd ?
 

I can give u an example.
In simulink : u set vcom=0,vref=+-1, and Amax=0.8;
In ckts : vdd=3.3v, vcom=1.5v,vref=+-1.5(0,and 3v) . so, Amax=0.8*1.5=1.2v(swing: 2.7v and 0.3v).
if ur opamp allow 0.3~2.7v swing, ckts will be ok.

Here,-Vref is 0v,which reaches the vss. So,u have to set ur Amax below vref.
if i set vref=+-500mv(means 1,and 2v),
Amax can exceed vref.
This should be determined in behavioral level.
 
but the input is so low

in practical , how it can be used to work
 

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