Delta-sigma modulators with improved noise performance
AssigneeCirrus Logic, Inc.
InventorsJohn Laurence Melanson, Yu Qing Yang
Life of this patent
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Abstract
An integrator stage for use in a delta sigma modulator includes an operational amplifier, an integration capacitor coupling an output of the operational amplifier and a summing node at an input of the operational amplifier, and a feedback path. The feedback path includes first and second capacitors having first plates coupled electrically in common at a common plate node and switching circuitry for sampling selected reference voltages onto second plates of the capacitors during a sampling phase. The integrator stage further includes a switch for selectively coupling the common plate node and the summing node during an integration phase.
Claims18
A delta-sigma modulator comprising:
- a quantizer;
- a loop-filter coupled to an input of the quantizer and receiving first and second feedback bits in response to an output of the quantizer, the loop-filter comprising:
- first and second capacitors each having an input plate and an output plate, the output plate of each of the first and second capacitors connected to a charge summing node with a fixed connection;
- first switching circuitry for coupling in an order selected by the first feedback bit one of first and second voltages to the input plate of the first capacitor during a charging phase and another of the first and second voltages to the input plate of the first capacitor during a charge transfer phase;
- and
- second switching circuitry for coupling in another order selected by the second feedback bit one of the first and second voltages to the input plate of the second capacitor during the charging phase and another of the first and second voltages to the input plate of the second capacitor during the charge transfer phase.
A method of reducing noise in a delta-sigma modulator comprising:
- generating a feedback bit and another feedback bit in a quantizer;
- providing a first voltage at a first node and a second voltage at a second node during a sampling phase;
- providing the second voltage at the first node and the first voltage at the second node during a charge transfer phase;
- coupling an input plate of a capacitor to a selected one of the first and second nodes in response to the feedback from a quantizer output;
- coupling an input plate of another capacitor to a selected one of the first and second nodes in response to the another feedback bit from the quantizer output;
- and
- summing charge from the capacitor and the another capacitor during the charge transfer phase at a summing node provided by fixed connection of respective output plates of the capacitor and the another capacitor.
A delta-sigma modulator comprising:
- an input summer for summing an input signal and a feedback signal;
- a loop-filter for filtering an output of the input summer;
- a quantizer for generating a multiple-bit output stream from an output of the loop filter;
- a feedback path for feeding-back first and second feedback bits to the input summer from the quantizer, the feedback path including a digital to analog converter comprising:
- first and second reference sampling capacitors, having output plates connected with a fixed connection to a summing node;
- first switching circuitry providing to a first node a first reference voltage during a sampling phase and a second reference voltage during a charge transfer phase and to a second node the second reference voltage during the sampling phase and the first reference voltage during the charge transfer phase;
- and
- second switching circuitry responsive to the first feedback bit generated by the quantizer to couple a selected one of the first and second outputs of nodes to an input plate the first reference sampling capacitor;
- and
- third switching circuitry responsive to the second feedback bit generated by the quantizer to couple a selected one of the first and second nodes to an input plate of the second reference sampling capacitor.
Dependencies are inferred from the claim text.