Demystifying Switched Capacitor Circuits

Demystifying Switched-Capacitor Circuits

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output levels are kept within the normalized range between 1 and −1. Thus, no extra

dynamic range scaling is needed. In this design, both DECT and GSM standards use

the same modulator topology shown in Figure 8.8, but at different OSRs—that is, for

DECT the OSR is changed to 64.

DS Modulator Design for WCDMA

As mentioned earlier, the ∆Σ modulator for WCDMA uses a much lower OSR than

192 (OSR = 24) to achieve a 56 dB SNR, therefore more aggressive noise-shaping is

needed. Here, an internal resonator feedback is added to optimize the NTF’s zeros,

as illustrated in Figure 8.10. Note that the feedback g