Multirate-multibit sigma-delta modulators

A multirate based band-pass sigma-delta modulator

“…This behavior is also present when the signal has more than one spectral component, for instance a random signal occupying the entire signal band. This effect was also observed in the multirate modulators described in [5]- [6]. Note that simulation results confirm the multirate character of the proposed modulator (first and second resonators working at the rates, fs and 2· fs, respectively) because the SNDR curve is in an intermediate position between those of a conventional modulator with OSR 32 and 64.…”

“…Unlike the well-known conventional 4 th -order one, the second resonator is replaced by an equivalent two-path circuit and, instead of reducing the high-pass filters clock rate to f s /2, it is maintained to f s . In a certain sense, the new architecture can be considered to be a multirate modulator [5]- [6] where the first integrator is clocked at a lower rate than the other integrators. In the proposed bandpass modulator the first resonator operates at the clock rate f s and the second one at the effective sampling frequency 2 · f s .…”

Electronic Implementation of Multirate Sigma-Delta Modulators Using CMOS Technologies

“…As shown in [18], the performances of the modulator in Fig. 1 are equal to those of a second-order conventional modulator with both integrators clocked at the intermediate rate f S /2.…”

“…Finally, multirate SDM's were introduced in [18,19] which reduce the frequency rate of the first integrator(s) of a single-loop SDM (or the first stage(s) of a cascade SDM). Modulator performances are preserved by increasing the rate of the rest of integrators (or stages), whose contribution to power consumption is negligible, by the same factor.…”

“…An antialiasing filter H(z) is required before the quantizer output is down-sampled and fed back to the modulator input. As shown in [18] a simple comb filter of order 2 can be used to avoid that aliasing deteriorates the performances of the modulator.…”