FEEDBACK TOPOLOGY DELTA-SIGMA MODULATOR HAVING AN AC-COUPLED FEEDBACK PATH
First Claim
1. A delta-sigma modulator, comprising:
- a loop filter comprising a plurality of cascaded integrator stages;
a quantizer having an input coupled to an output of a final one of said plurality of cascaded integrator stages; and
a feedback network providing feedback from an output of said quantizer to inputs of at least two of said plurality of integrator stages through a plurality of corresponding feedback paths, and wherein only one of said feedback paths provides a direct current feedback path from said output of said quantizer to a corresponding given one of said at least two integrator stages.
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Abstract
A feedback topology delta-sigma modulator having an AC-coupled feedback path reduces signal level in the loop filter, easing linearity requirements and reduces capacitor size requirements for the filter integration stages. The delta-sigma modulator includes a loop filter having multiple integrator stages, a quantizer, and a feedback network providing at least two feedback paths to corresponding integrators in the loop filter. In one aspect, only one of the feedback paths from the quantizer output is DC coupled, and at least one other of the feedback paths is DC-coupled, which reduces the signal levels in the loop filter integrators. In another aspect, at least one of the feedback paths from the quantizer is AC coupled, providing a similar result. The AC feedback path may be provided through a series-connected resistor and capacitor. The DC feedback path may be provided through a resistor, a switched-capacitor network, or may be a quantizer-controlled current source.
82 Citations
21 Claims
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1. A delta-sigma modulator, comprising:
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a loop filter comprising a plurality of cascaded integrator stages; a quantizer having an input coupled to an output of a final one of said plurality of cascaded integrator stages; and a feedback network providing feedback from an output of said quantizer to inputs of at least two of said plurality of integrator stages through a plurality of corresponding feedback paths, and wherein only one of said feedback paths provides a direct current feedback path from said output of said quantizer to a corresponding given one of said at least two integrator stages. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A delta-sigma modulator, comprising:
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a loop filter comprising a plurality of cascaded integrator stages; a quantizer having an input coupled to an output of a final one of said plurality of cascaded integrator stages; and a feedback network providing feedback from an output of said quantizer to said loop filter through at least one feedback path, and wherein at least one of said feedback paths is an feedback path blocking direct current signals and passing only time-varying signals from said output of said quantizer to a corresponding one of said integrator stages. - View Dependent Claims (14, 15, 16, 17, 18, 19)
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20. A method of operating a delta-sigma modulator, comprising:
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noise-shaping an input and feedback signals with a loop filter formed by a plurality of cascaded integrator stages; quantizing a result of said noise-shaping to provide an output signal; and providing feedback of said quantizing to said noise-shaping as said feedback signals, wherein said providing provides feedback of direct current values to only one input of said plurality of cascaded integrator stages.
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21. A method of operating a delta-sigma modulator, comprising:
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noise-shaping an input and feedback signals with a loop filter formed by a plurality of cascaded integrator stages; quantizing a result of said noise-shaping to provide an output signal; and providing feedback of said quantizing to said noise-shaping as said feedback signals, wherein said providing blocks feedback of direct current values in at least one feedback path to at least one corresponding one of said plurality of cascaded integrator stages.
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Specification