MPhil thesis of Lo Chi Wa - Department of Electronic & Computer ...

the residue and the carry-out signal in this case. Based on this, the accumulator can bemodeled as Fig. 61b which has a delay at the residue output and the delayed residue isfeedback to the input. Without affecting the performance, we can add an extra delay atthe carry-out externally. Then we can shift the delays to the output of the adder, asshown in Fig. 61c. Finally, the feedback path splits into two and the accumulatorbecomes exactly the same as the first-order modulator, by comparing the model in Fig.59 and Fig. 61d.+-Z -1 + -(1-Z -1 ) 23b+-Z -1 + -Z -1 (1-Z -1 )2b3b10b +-Z -1 + -Z -21bFig. 59 System diagram of MESH-3 Sigma-Delta modulator68