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1 Prace Przemysłowego Instytutu Elektroniki

1 1998

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Measurement and enhancement of multistage sigma-delta modulators

Hejn K., Murphy P., Kale I.

Prace Przemysłowego Instytutu Elektroniki

1998

nr 132

18-24

Over-sampled sigma-delta modulators are at present the only solution to realizing high resolution (>16 bits) A/D converters. They are relacively robust against circuit imperfections and well suited for VLSI implementation. Their theoretical basis is well founded in many excellent papers. However, it has to be pointed out that those analyses have not considered effects such as gain mismatch of the stages, timing. Ditters, input noise. Instability of thresholders the asymmetry in the rise fall times of the pulses generated etc. Knowing sigma-delfa modulators theory is not the same as knowing what to do when asked to measure a signal spectrum with 1 dB resolution or -130 dB harmonic distortion. These numerical values are typical for sigma-delta structures with 20-bit potential. This paper specifically addresses such problems suggests some solutions. Simulations known that the key factors are: a coherent measurement event (explicit) digitizing and polyphase recursive all-pass filtering.