Idle Tone Behavior in Sigma Delta Modulation
This paper examines the relationship between various unwanted phenomena that plague audio engineers in the design of Sigma Delta Modulators. This work aims to clarify the difference and relationship between single DC idle tones, long limit cycles, short limit cycles and ‘periodic’ short limit cycles, while extending the current knowledge in idle tone behavior. A relationship between the periodic input to the quantizer of a 1-bit Delta Sigma Modulator and the appearance of idle tones is shown. It is shown that for a large range of input signal magnitudes, the fundamental frequency of idle tones is proportional to the DC input. This finding has also been used to examine idle tone aliasing. Numerous simulations are reported which confirm these findings.
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