Multiple stage delta sigma modulators
First Claim
1. A delta sigma modulator for use with a delta sigma frequency synthesizer, the modulator comprising:
- a first group of accumulators;
a second group of accumulators;
a recombiner producing an output of said modulator; and
a bit stream generator, wherein each group of accumulators comprises a plurality of accumulators coupled to one another;
said second group of accumulators receives an input representing a fractional portion of divider division ratio used by said delta sigma frequency synthesizer;
said first group of accumulators receives input from said second group of accumulators;
at least one accumulator in said second group of accumulators receives an input from said bit stream generator;
said recombiner receives input from said first group of accumulators; and
both of said first and second groups of accumulators are synchronously clocked.
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Abstract
A delta sigma modulator which employs a plurality of accumulators with non-power-of-2 modulus. The accumulators may consist of a primary non-power-of-2 modulus accumulator and a secondary non-power-of-2 modulus accumulator. The number of bits in the primary accumulators affects the frequency resolution of the resultant delta sigma fractional N frequency synthesizer and can be the minimum number of bits required by the resolution specification. The secondary accumulator integrates the carry outputs of its corresponding primary accumulators. This integration results in attenuating the dc content of the modulator output by a factor equal to the modulus of the secondary accumulators and may require compensation in the recombination block.
33 Citations
17 Claims
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1. A delta sigma modulator for use with a delta sigma frequency synthesizer, the modulator comprising:
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a first group of accumulators;
a second group of accumulators;
a recombiner producing an output of said modulator; and
a bit stream generator, wherein each group of accumulators comprises a plurality of accumulators coupled to one another;
said second group of accumulators receives an input representing a fractional portion of divider division ratio used by said delta sigma frequency synthesizer;
said first group of accumulators receives input from said second group of accumulators;
at least one accumulator in said second group of accumulators receives an input from said bit stream generator;
said recombiner receives input from said first group of accumulators; and
both of said first and second groups of accumulators are synchronously clocked. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 17)
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11. A delta sigma modulator for use in a delta sigma frequency synthesizer, the delta sigma modulator comprising:
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a first group of cascaded accumulators, said first group of accumulators including at least one accumulator having a modulus selected from a group of values which excludes 2n, n being a natural number, at least one of said first group of accumulators receiving an input from another of said first group of accumulators;
a second group of cascaded accumulators, at least one of said second group of accumulators receiving an input from another of said second group of accumulators;
a recombiner producing an output of said modulator; and
a bit stream generator, wherein at least one of said first group of accumulators receives an input from one of said second group of accumulators;
each one of said second group of accumulators has a modulus equal to a ratio between a frequency input to said synthesizer and a desired frequency resolution;
each one of said accumulators in said first group produces an output received by said recombiner; and
at least one of said accumulators in said second group of accumulators receives an output of said generator. - View Dependent Claims (12, 13, 14, 15, 16)
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Specification