Cascaded sigma-delta modulators for fractional-N-division phase-lock-loop frequency systhesizer

摘要

A composite modulator includes a cascade of Sigma-Delta modulators each as shown in figure 6 and connected (as shown in Figure 11) so that the output e of the latch 65 of each modulator is coupled to the input of the adder 61 of the following modulator. The output Y of the logic stage 62 of each modulator is coupled to the common combination stage 115 to produce an output of the composite modulator. The composite modulator is particularly suitable as a component of the fractional N feedback controller in the phase lock loop of a frequency synthesizer.