| 摘要 |
This invention is concerned with digital-to-analogue converters and more particularly relates to techniques for reducing signal dependent loading of reference voltage sources. A switched capacitor digital-to-analogue converter (DAC) 400 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 112 and second 114 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 404, 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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