One-bit switched-capacitor D/A circuit with continuous time linearity
First Claim
1. A data conversion system including digital-to-analog converter having a digital input and an analog output, the digital input for receiving a digital signal and having at least a first logic state and a second logic state, and outputting a continuous time analog output signal on the analog output, the digital-to-analog converter comprising:
- a first circuit responsive to the presence of the first logic state on the digital input for causing the analog output to change in value independent of the output in accordance with a predetermined transfer function, said change in value being substantially the same each time the first logic state is present on the digital inputa second circuit responsive to the presence of the second logic state on the digital input for causing the analog output to change in value independent of the output in accordance with said predetermined transfer function, said change in value caused by said second circuit being substantially the same each time the second logic state is present, the analog output signal on the analog output having a substantially linear response in the continuous time domain due to said first and second circuits, anda redistribution circuit operable to limit the DC gain of said predetermined transfer function to a known and fixed quantity.
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Accused Products
Abstract
A modified lossy integrator digital-to-analog converter includes an amplifier (46) that receives an input on a summing node (48) and provides an output on a node (52). A feedback capacitor (50) is disposed across the input and output and has an output switched-capacitor (54) disposed in parallel therewith to passively distribute the charge thereacross. Switches (60) and (66) are operable to control the switching operation of the capacitor (54). Two input switched capacitors (70) and (94) are controlled by associated switches to switch charge onto the summing node (48) in a first clock cycle φ2. A one-bit data stream modulates the operation such that either the charge from the capacitor (78) is dumped onto the summing node (48) or the charge from the capacitor (94) is dumped onto the summing node (48). This operation during the φ2 cycle provides an integrated output that is slew-limited. The full charge of the selected capacitor (78) or (94) is allowed to be completely dumped onto the node (48) prior to the output switched capacitor (54) being disposed across the feedback capacitor (50). This allows for a linear operation in this range. Thereafter, the charge is passively distributed across the feedback capacitor (50) in a linear fashion associated with the lossy integrator. This provides a conversion from a digital signal one-bit data stream to a continuous time output analog signal.
37 Citations
14 Claims
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1. A data conversion system including digital-to-analog converter having a digital input and an analog output, the digital input for receiving a digital signal and having at least a first logic state and a second logic state, and outputting a continuous time analog output signal on the analog output, the digital-to-analog converter comprising:
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a first circuit responsive to the presence of the first logic state on the digital input for causing the analog output to change in value independent of the output in accordance with a predetermined transfer function, said change in value being substantially the same each time the first logic state is present on the digital input a second circuit responsive to the presence of the second logic state on the digital input for causing the analog output to change in value independent of the output in accordance with said predetermined transfer function, said change in value caused by said second circuit being substantially the same each time the second logic state is present, the analog output signal on the analog output having a substantially linear response in the continuous time domain due to said first and second circuits, and a redistribution circuit operable to limit the DC gain of said predetermined transfer function to a known and fixed quantity. - View Dependent Claims (2, 3)
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4. A data conversion system having a digital-to-analog converter for receiving a one-bit digital input data stream having first and second states and outputting a continuous time analog signal, the digital-to-analog converter comprising:
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an integration stage having an amplifier with a summing input node and an output node, and a feedback capacitor disposed between said summing input node and said output node; an input charging device operating in first and second modes, said input charging device in said first mode operable to input a finite amount of charge to said summing node and, in a said second mode, operable to extract a finite amount of charge from said summing node; an output capacitance device for selectively disposing an output capacitance across said feedback capacitor to distribute the charge on said feedback capacitor between said feedback capacitor and said output capacitance; and a switching device for controlling said input charging device to connect said input charging device to said summing node during a first time period to selectively add charge thereto or selectively extract charge therefrom, said switching device operable to select said first mode in said input charging device for the first state of the input digital data stream and to select said second mode in said input charging device for the second state of the digital input data stream, said switching device also operable to control said output capacitance device to connect said output capacitance across said feedback capacitor during a second and subsequent time period. - View Dependent Claims (5, 6, 7, 8, 9)
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10. A method for converting a one-bit digital input data stream having first and second logic states to a continuous time analog output signal, comprising the steps of:
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providing a summing node and an output node; disposing an integration stage between the summing node and the output node, the integration stage operable to integrate charge supplied to the summing node across a feedback capacitor disposed between the summing and output nodes to provide an integrated output signal on the output node; adding a first predetermined amount of charge to the summing node during a first time period in the presence of the first logic state of the digital input data stream; extracting a predetermined amount of charge from the summing node during the first time period and in the presence of a second logic state of the digital input signal; and disposing an output capacitor across the feedback capacitor during a second time period subsequent to the first time period to distribute the charge in the feedback capacitor across the output capacitor and the feedback capacitor. - View Dependent Claims (11, 12, 13)
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14. A digital-to-analog converter for receiving a one-bit digital input data stream having first and second states and outputting a continuous time differential analog signal, comprising:
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an integration stage having a differential amplifier with a positive summing input node, a positive output node, a negative summing input node, and a negative output node, and first and second feedback capacitors disposed between said positive and negative summing input nodes and said positive and negative output nodes; positive and negative input charging devices, each of said positive and negative input charging devices operating in first and second modes, in said first mode said input charging devices operable to input a finite amount of charge to said positive and negative summing nodes and, in said second mode, operable to extract a finite amount of charge from said positive and negative summing nodes; first and second output capacitance devices associated with said first and second feedback capacitors, respectively, for disposing respective first and second output capacitances across said first and second feedback capacitors to distribute the charge on said first and second feedback capacitors between said respective first and second feedback capacitors and said respective output capacitances; and a switching device for controlling said positive and negative input charging devices to operate in said first mode for the first state of the input digital data stream and to operate in said second mode for the second state of the digital input data stream, said switching device operable to connect said positive and negative input charging devices to said positive and negative summing input nodes during a first time period to selectively add charge thereto or selectively subtract charge therefrom and connecting said first and second output capacitances across said respective first and second feedback capacitors during a second and subsequent time period.
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Specification