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Abstract

A delta sigma modulator system includes a delta sigma modulator (9) including a summing circuit (3) having a first input connected to receive an input signal (2), loop filter circuitry (5) having an input coupled to an output of the summing circuit (3), and comparator circuitry (22) having an input coupled to an output of the loop filter circuitry (5) and also having an output coupled to an output (23) of the delta sigma modulator (9). The density of the dither is adjusted in accordance with changes in the magnitude of the input signal. This is accomplished by performing a coarse digital filtering of an output signal (23) produced by the delta-sigma modulator (9), wherein noise present in the output signal (23) produced by the delta sigma modulator (9) causes a probability distribution of the occurrence of pulses constituting a filtered output signal (25) produced by the coarse filtering. A dither disable signal is produced if the filtered output signal (25) is not within a first threshold window. The dither disable signal is utilized to enable a pseudo-random sequence signal in order to produce a non-zero dither signal level. The non-zero dither signal is applied to the second input of the second summing circuit (10). The coarse digital filtering produces the probability distribution so as to cause gradual transitions in the density of pulses produced by the coarse filtering.

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