US 2006/0232459 A1Published application

Digital to analog converter

AssigneeAnalog Devices, Inc.

InventorsDennis Dempsey, Thomas O'Dwyer

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Abstract

The present invention provides an improved Digital to Analog Converter (DAC) of the switched dual string DAC type, which saves on chip surface area, reduces the number of resistors and implementation cost, reduces the self capacitance and the device leakage currents of the circuit elements. The invention provides a guaranteed monotonic DAC architecture, which comprises a switching network for creating three states at a DAC transition node. In one embodiment the invention provides an unloaded state wherein a LSB DAC is de-coupled from a MSB DAC wherein the node between neighbouring MSB DAC resistors is coupled to the DAC output. One of the advantages of creating the unloaded state is that the number of LSB DAC resistors is reduced as is normally the case in the prior art for a similar application.

Claims18

Dependent claims

A digital to analog converter (DAC), comprising:

a pair of resistor strings, a first one of the resistor strings being adapted for coupling across a voltage supply, resistors in the first resistor string producing voltages in response to current fed thereto from the voltage supply and a second one of the resistor strings;
a switching network adapted to couple a voltage produced across a selected one of resistors in the first string across the second one of the resistor strings in response to a digital input signal, said digital input signal comprising a digital bit stream, the resistors in the second resistor string producing voltages in response to current passing from the first resistor string through the second resistor string through said switching network to produce a corresponding analog signal to said digital input signal to an output;
and
wherein the switching network is adapted to provide an unloaded state generated when a Least Significant Bit (LSB) resistor of said DAC, associated with said first resistor string, is de-coupled from a Most Significant Bit (MSB) resistor of said DAC, associated with said second resistor string, of said digital input signal by said switching network.

1 more element

Dependencies are inferred from the claim text.