naderi
New Member
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Posts: 8
Canada
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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,
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