Hello all,

What can limit the input signal level for a delta sigma modulator?
and How can the maximum stable input be increased?

I used an example given in the delta-sigma toolbox from Matlab and optimized a 3rd-order NTF for:
-Continuous-time with RZ DAC
-all poles at DC.
-out-of-band noise: Hinf=1.7
-BW = 20kHz
-OSR = 128
-cascaded-integrator-feedback (CIFB) structure.
(fs=5.12MHz, U(1:3)=[0.1727, 0.7209, 1.4812])

After optimization and conversion to continuous-time, I tested in time-domain by the simulink. It seems that the maximum input signal level cannot be above 1/4 of U1 (coefficient of the outer feedback loop shown in the figure), which is 0.043. Otherwise the modulator becomes unstable. Such a low input makes problem for a resolution above 13 bits as it can be limited by thermal noise floor of the modulator.

I appreciate your comments.

Thanks,

Thanks for your reply.
Could you please elaborate why resolution of the quantizer effects on MSA?

Best,
Ali

Yes, Thanks a lot.

Ali