Apparatus and method for resetting delta-sigma modulator state variables using feedback impedance
AssigneeSilicon Laboratories Inc.
InventorsAndrew W. Krone, David R. Welland
Life of this patent
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Abstract
A technique for resetting state variables of a delta-sigma modulator of an analog-to-digital converter. A switched capacitor impedance is placed in the reset feedback path of an integrator to ensure that the integrator tracks to the proper reset voltage, when reset is initiated in a third-order or higher delta-sigma modulator.
Claims30
An apparatus for resetting a state variable output of an integrator stage of a modulator utilized in an analog-to-digital converter when an unstable condition is detected comprising:
- a reset switch coupled in a reset feedback path between an input and an output of the integrator stage;
- an impedance coupled in series with the reset feedback path between the input and output of the integrator stage, wherein activation of the reset switch inserts said impedance in the reset feedback path;
- and
- said impedance causing the integrator stage to operate as a lossy integrator and to prevent the integrator from operating as a unity gain amplifier to ensure that the state variable output of the integrator stage tracks to a desired stable reset state.
In an analog-to-digital converter, a modulator for converting an analog signal to a digital signal comprising:
- a plurality of integrator stages coupled serially to provide a delta-sigma modulator configuration which is higher than a second-order of operation;
- a reset switch coupled in a reset feedback path between an input and an output of one of the integrator stages beyond a second level to reset its state variable to a stable reset state;
- an impedance coupled in series with said reset switch and also coupled between the input and output of the integrator stage, wherein activation of the reset switch inserts said impedance in the reset feedback path;
- and
- said impedance causing the integrator stage to operate as a lossy integrator and to prevent the integrator from operating as a unity gain amplifier to ensure that the output of the integrator stage tracks to a desired stable reset state.
A method of resetting a state variable output of an integrator stage of a modulator utilized in an analog-to-digital converter when an unstable condition is detected, but ensuring that a reset condition places the state variable in a stable state for integrator stages operating with non-grounded inputs, comprising the steps of:;
- detecting an occurrence of an unstable state of the modulator
- activating a reset condition in response to the detecting of the unstable state;
- inserting an impedance between the input and output of the integrator stage when the reset condition is activated to cause the integrator to operate as a lossy integrator and to prevent the integrator stage from operating as a unity gain amplifier to ensure that the output of the integrator stage tracks to a desired stable reset state.
A communication system, in which a non-AC powered circuitry is coupled to a transmission medium and in which isolation is required between the non-AC powered circuitry and an AC powered circuitry, for receiving an analog signal from one or the other side of the isolation barrier, converting the analog signal to a digital signal and transferring a digital signal across the isolation barrier comprising:
- a capacitive barrier coupled to the AC powered circuitry and non-AC powered circuitry for providing isolation between the two circuitry;
- and
- an analog-to-digital converter in one of said circuitry coupled to receive the analog signal, convert it and transfer a digital signal across said capacitive barrier, said analog-to-digital converter comprising:
- (a) a modulator comprised of a plurality of integrator stages coupled serially to provide a delta-sigma modulator configuration which is higher than a second-order of operation;
- (b) a reset switch coupled in a reset feedback path between an input and an output of one of the integrator stages beyond a second level to reset its state variable to a stable reset state;
- (c) an impedance coupled in series to said reset switch and also coupled between the input and output of the integrator stage, wherein activation of the reset switch inserts said impedance in the reset feedback path;
- and
- said impedance causing the integrator stage to operate as a lossy integrator and to prevent the integrator from operating as a unity gain amplifier to ensure that the output of the integrator stage tracks to a desired stable reset state.
An apparatus for resetting state variables of an integrator stage in a modulator of an analog-to-digital converter comprising:
- a reset switch;
- and
- an impedance connected in series with the reset switch, wherein the series combination of the reset switch and impedance is connected between an input and an output of the integrator stage forming a feedback path between the input and the output through the impedance and the reset switch, and wherein activation of the reset switch connects the feedback path between the input and the output of the integrator stage.
Dependencies are inferred from the claim text.