Noise reduction in voltage reference signal
First Claim
1. An apparatus, comprising:
- a switched-capacitor circuit comprising a reference voltage input node, wherein the switched-capacitor circuit comprises a capacitor comprising a first terminal and a second terminal, and wherein the switched-capacitor circuit further comprises a first switch coupled to the first terminal, and wherein the switched-capacitor circuit further comprises a second switch coupled to the second terminal;
a variable resistor coupled between the reference voltage input node and components of the switched-capacitor circuit; and
a controller configured to adjust the variable resistor, wherein the controller is configured;
to set a resistance value of the variable resistor at a first level during a first time period; and
to set the resistance value of the variable resistor at a second level higher than the first level during a second time period,wherein the first time period and the second time period are at least part of a first sampling period of the switched-capacitor circuit,wherein the first switch and the second switch are closed for the duration of the first sampling period, andwherein the controller is further configured to not short the resistor during a zeroth time period before the first time period, wherein the zeroth time period, the first time period, and the second time period comprise the first sampling period of the switched-capacitor circuit.
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Accused Products
Abstract
A variable resistor may be coupled between a reference voltage source and components of an integrated circuit to reduce issues relating to thermal noise from a reference voltage signal generated by the reference voltage source. The variable resistor may be set to a low level during a first time period and a high level during a second time period, in which the time periods correspond to a sampling period of a switched-capacitor circuit. The low resistance time period may allow quick settling of an input reference voltage signal, whereas the high resistance time period may reduce a bandwidth of noise on a sampling capacitor coupled to the reference voltage signal. The variable resistor and switched-capacitor network may be used in an analog-to-digital converter (ADC), such as in audio circuits.
28 Citations
16 Claims
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1. An apparatus, comprising:
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a switched-capacitor circuit comprising a reference voltage input node, wherein the switched-capacitor circuit comprises a capacitor comprising a first terminal and a second terminal, and wherein the switched-capacitor circuit further comprises a first switch coupled to the first terminal, and wherein the switched-capacitor circuit further comprises a second switch coupled to the second terminal; a variable resistor coupled between the reference voltage input node and components of the switched-capacitor circuit; and a controller configured to adjust the variable resistor, wherein the controller is configured; to set a resistance value of the variable resistor at a first level during a first time period; and to set the resistance value of the variable resistor at a second level higher than the first level during a second time period, wherein the first time period and the second time period are at least part of a first sampling period of the switched-capacitor circuit, wherein the first switch and the second switch are closed for the duration of the first sampling period, and wherein the controller is further configured to not short the resistor during a zeroth time period before the first time period, wherein the zeroth time period, the first time period, and the second time period comprise the first sampling period of the switched-capacitor circuit. - View Dependent Claims (2, 3, 4, 5, 6)
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7. An apparatus, comprising:
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a switched-capacitor circuit comprising a reference voltage input node, wherein the switched-capacitor circuit comprises a capacitor comprising a first terminal and a second terminal, and wherein the switched-capacitor circuit further comprises a first switch coupled to the first terminal, and wherein the switched-capacitor circuit further comprises a second switch coupled to the second terminal; a variable resistor coupled between the reference voltage input node and components of the switched-capacitor circuit; and a controller configured to adjust the variable resistor, wherein the controller is configured; to set a resistance value of the variable resistor at a first level during a first time period; and to set the resistance value of the variable resistor at a second level higher than the first level during a second time period, to not short the resistor during a zeroth time period before the first time period, wherein the zeroth time period, the first time period, and the second time period comprise the first sampling period of the switched-capacitor circuit, and wherein the first switch and the second switch are closed for at least the duration of the first time period and the second time period of the first sampling period, wherein the switched-capacitor circuit is part of an analog-to-digital converter (ADC), and the reference voltage input node is coupled to an on-chip reference voltage generator.
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8. A method of reducing noise coming from an on-chip reference in a switched-capacitor circuit, wherein the switched-capacitor circuit comprises a capacitor comprising a first terminal and a second terminal, and wherein the switched-capacitor circuit further comprises a first switch coupled to the first terminal, and wherein the switched-capacitor circuit further comprises a second switch coupled to the second terminal, the method comprising:
controlling a variable resistor coupled between the switched-capacitor circuit and the on-chip reference by performing steps comprising; setting a resistance value of the variable resistor at a first level during a first time period of a first sampling period of the switched-capacitor circuit; and setting the resistance value of the variable resistor at a second level higher than the first level during a second time period of the switched-capacitor circuit, wherein the first time period and the second time period are at least part of a first sampling period of the switched-capacitor circuit, wherein the first switch and the second switch are closed for the duration of the first sampling period, and wherein the step of controlling the variable resistor further comprises the step of setting the resistance value of the variable resistor at a third level lower than the second level during a zeroth time period before the first time period. - View Dependent Claims (9, 10, 11, 12)
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13. A method of reducing noise coming from an on-chip reference in a switched-capacitor circuit, comprising:
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providing a first switch and a second switch and a capacitor coupled through a first terminal and a second terminal to the first switch and the second switch, respectively, to form the switched-capacitor circuit; coupling an artifact reduction network (ARN) between the switched-capacitor circuit and an output of a buffer of the on-chip reference, wherein the ARN is transparent during a first time period of a sampling phase to not affect settling accuracy and is activated during another portion of the sampling phase to limit sampling network bandwidth during a second time period of the sampling phase, wherein the first switch and the second switch are closed for the duration of the first sampling period; and controlling the artifact reduction network (ARN) to set the resistance value of the artifact reduction network (ARN) at a third level lower than the second level during a zeroth time period before the first time period. - View Dependent Claims (14, 15, 16)
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Specification