Coded data generation or conversion – Analog to or from digital conversion – Digital to analog conversion
Reexamination Certificate
1999-08-12
2001-08-21
Young, Brian (Department: 2819)
Coded data generation or conversion
Analog to or from digital conversion
Digital to analog conversion
Reexamination Certificate
active
06278393
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to digital-to-analog converters (DACs), and more particularly to such converters capable of converting more than one digital input to corresponding analog outputs.
BACKGROUND OF THE INVENTION
Digital-to-analog converters are used to convert digitally coded signals to an analog signal, or in conjunction with successive approximation circuitry as part of an analog-to-digital converter. DACs may employ a voltage applied across a resistor string or a current driven resistor string. Switches, such as transistors, couple intermediate taps at the resistor junctions, and sometimes at the resistor-potential junctions, to an output node. The digitally coded signal is decoded to determine which switches to turn on. The magnitude of an analog voltage produced at the output node depends on which switches are turned on. Heretofore, for each digital input and corresponding required analog output, a separate resistor string was required.
What is needed is a digital-to-analog converter that can utilize a single resistor string to provide multiple analog outputs, with each analog output corresponding to a digitally coded signal provided as an input.
SUMMARY OF THE INVENTION
In accordance with an illustrative embodiment of the invention, an integrated circuit includes a digital-to-analog converter in which a resistor string is adapted to be coupled to a reference source. The resistor string includes a plurality of serially coupled impedances defining intermediate taps at the junctions thereof. A first plurality of switches are coupled between a first output node and respective ones of the intermediate taps. A first selection circuit receives a first digitally coded signal and is coupled to each switch in the first plurality of switches. The first selection circuit selectively switches the first plurality of switches to predetermined states depending upon the first digitally coded signal to generate a first analog output. A second plurality of switches are coupled between a second output node and respective ones of the intermediate taps. A second selection circuit receives a second digitally coded signal and is coupled to each switch in the second plurality of switches. The second selection circuit selectively switches the second plurality of switches to predetermined states depending upon the second digitally coded signal to generate a second analog output.
REFERENCES:
patent: 6037889 (2000-03-01), Knee
patent: 6049300 (2000-04-01), Shoval
Lopata Douglas D.
Smith Malcolm Harold
Agere Systems Guardian Corp.
Smith David L.
Young Brian
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