Excess loop delay in continuous-time delta-sigma modulators

Continuous-time (CT) delta-sigma modulators (/spl Delta//spl Sigma/M's) suffer from a problem not seen in discrete-time (DT) designs, that of excess loop delay: nonzero delay between the quantizer clock edge and the time when a change in output bit is seen at the feedback point in the modulator...

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Bibliographic Details
Published in:IEEE transactions on circuits and systems. 2, Analog and digital signal processing Analog and digital signal processing, 1999-04, Vol.46 (4), p.376-389
Main Authors: Cherry, J.A., Snelgrove, W.M.
Format: Article
Language:English
Subjects:
Analog-digital conversion, digital-analog conversion, pcm coding
Applied sciences
Bandwidth
Clocks
Delay effects
Delta modulation
Dynamic range
Exact sciences and technology
Filters
Information, signal and communications theory
Modulation, demodulation
Signal and communications theory
Signal design
Switching circuits
Telecommunications and information theory
Voltage
White noise
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Summary:Continuous-time (CT) delta-sigma modulators (/spl Delta//spl Sigma/M's) suffer from a problem not seen in discrete-time (DT) designs, that of excess loop delay: nonzero delay between the quantizer clock edge and the time when a change in output bit is seen at the feedback point in the modulator. This paper analytically shows how such delay affects the equivalence between the CT modulator loop filter and its DT counterpart. The effect of this delay on modulator dynamic range is studied through simulation for the standard double-integration (low pass) CT modulator and its equivalent fourth-order f/sub s//4 band pass circuit. For the first time, the results are extended to higher order low-pass and bandpass designs, as well as multibit designs. Methods for alleviating the performance loss caused by excess loop delay are also discussed.
ISSN:1057-7130
1558-125X
DOI:10.1109/82.755409