DAC using current source driving main resistor string
AssigneeCygnal Integrated Products, Inc.
InventorsKa Y. Leung, Douglas R. Holberg
Life of this patent
Estimating the term…
Abstract
An digital-to-analog converter having main DAC resistor strings and sub-DAC resistor strings for converting MSB and LSB portions of a digital word into corresponding analog voltages. The main DAC resistor strings are driven by constant current sources to improve the linearity of the conversion process. The constant current sources present a high impedance to the main DAC resistor strings, thereby providing a more linear change in resistance during the conversion process, and reducing second-order harmonic nonlinearity.
Claims24
A digital-to-analog converter, comprising:
- a first resistor string for generating a plurality of analog voltages;
- a second resistor string for generating a plurality of analog voltages;
- a selection circuit responsive to one or more most significant bits of a digital word for selecting an analog voltage from said first resistor string, and for coupling the selected analog voltage to said second resistor string;
- and
- a high impedance driver for driving said first resistor string, thereby providing improved linearity in the digital-to-analog conversion.
A method of providing digital-to-analog conversion, comprising the steps of:
- driving a first resistor string having a plurality of nodes to produce a corresponding plurality of different voltages;
- driving said first resistor string with a high impedance source to thereby reduce non-linearity errors;
- coupling one of said plurality of different voltages from said first resistor string to a second resistor string;
- selecting one said voltage of said plurality of different voltages for coupling to said second resistor string, as a function of bits of a digital word;
- and
- providing an analog output voltage from said second resistor string.
A digital-to-analog converter, comprising:
- a first main DAC resistor string;
- a second main DAC resistor string;
- respective constant current sources driving said first and second main DAC resistor strings;
- a first sub-DAC resistor string;
- a second sub-DAC resistor string;
- respective constant current sources driving said first and second sub-DAC resistor strings;
- a constant current driven in each said sub-DAC resistor string being a predefined ratio of current driven in each said main DAC resistor string, said current ratio being a function of a ratio of resistance of a main DAC resistor string to a sub-DAC resistor string;
- a first switch multiplexer for selecting a voltage from each said main DAC resistor strings as a function of bits of a digital word, and coupling the selected voltages to said sub-DAC resistor strings;
- and
- a second switch multiplexer for selecting a voltage from said sub-DAC resistor strings as a function of other bits of the digital word.
Dependencies are inferred from the claim text.