Digital-to-analogue converter circuits
First Claim
1. A switched capacitor digital-to-analogue converter (DAC) comprising an active circuit with a feedback element, the feedback element comprising a feedback capacitor, a second capacitor and a switch to connect the second capacitor to one of first and second references to store charge on the second capacitor and to connect the second capacitor in parallel with the feedback capacitor to share said stored charge with the feedback capacitor;
- wherein the switch is further configured to connect the second capacitor to a substantially signal-independent reference prior to connection of the second capacitor to said one of said first and second references.
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Abstract
A switched capacitor digital-to-analogue converter (DAC) 400 for reducing signal dependent loading of a reference voltage source used by the converter comprises an active circuit (102) with a feedback element. The feedback element comprises a feedback capacitor (104), a second capacitor (106) and switches (402, 110) to connect the second capacitor to one of first and second reference sources to store charge on the second capacitor and to connect the second capacitor in parallel with the feedback capacitor to share said stored charge with the feedback capacitor. The switch is further configured to connect the second capacitor to a substantially signal-independent reference prior to connection of the second capacitor to said one of said first and second references. Connecting the second capacitor to a substantially signal-independent reference source prior to the selected first or second reference gives a linear signal-dependent loading of the first and second reference sources. Connecting two such circuits with anti-phase signals then causes these linear dependences to cancel, giving a substantially signal-independent loading of these reference sources.
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Citations
18 Claims
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1. A switched capacitor digital-to-analogue converter (DAC) comprising an active circuit with a feedback element, the feedback element comprising a feedback capacitor, a second capacitor and a switch to connect the second capacitor to one of first and second references to store charge on the second capacitor and to connect the second capacitor in parallel with the feedback capacitor to share said stored charge with the feedback capacitor;
- wherein the switch is further configured to connect the second capacitor to a substantially signal-independent reference prior to connection of the second capacitor to said one of said first and second references.
- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A feedback element for a switched capacitor DAC comprising:
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a feedback capacitor;
a second capacitor;
a switch; and
a clock generator; and
wherein the clock generator is configured to control the switch to connect the second capacitor to one of first and second references to store charge on the second capacitor and to connect the second capacitor in parallel with the feedback capacitor to share said stored charge with the feedback capacitor, and wherein the clock generator is further configured to connect the second capacitor to a substantially signal-independent reference prior to connection of the second capacitor to said one of said first and second references. - View Dependent Claims (13, 14, 15)
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- 16. A switched capacitor digital-to-analogue converter in which a switched capacitor is repetitively and selectively connected to a positive and to a negative reference voltage and to a charge storage capacitor to controllably share charge with the charge storage capacitor, the digital-to-analogue converter further comprising switch means for bringing the charge on the switched capacitor to a substantially predetermined state before said connection of the switched capacitor to a said reference voltage.
Specification