| 摘要 |
Sigma-delta modulator comprising a low-pass filter of the Nth order, which is constituted by a series combination of N first-order integrating sections (6.1, 6.2, 6.3, ..., 6.N) comprising each an integrator (12.1, 12.2, 12.3, ..., 12.N) and a limiter (14.1, 14.2, 14.3, ..., 14.N). The individual output signals of the sections are weighted by means of corresponding weighting amplifiers (16.1, 16.2, 16.3, ..., 16.N) and added together in an adder stage (18). The gains of the sections and the limiting values of the limiters are selected so that the last limiter (14.N) in the series arrangement is activated first when the signal level in the sigma-delta modulator increases, subsequently the last-but-one limiter, and so on. This reduces the order of the filter system each time by one when there is an increasing signal level, and causes the sigma-delta modulator to remain stable. <IMAGE>
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