Reference ladder auto-calibration circuit for an analog to digital converter
AssigneeDavid Sarnoff Research Center, Inc.
InventorDonald J. Sauer
Life of this patent
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Abstract
An auto-calibrated reference resistor ladder network is disclosed which is suitable for use in a precision analog to digital converter. Resistors in the ladder are connected to an auto-calibration circuit which continually measures the potential developed across each of the connected resistors and adjusts the resistance of the resistor to match the measured potential to a reference potential. In the disclosed circuit, the reference potential is the potential developed across a defined one of the resistors.
Claims10
Apparatus which provides a plurality of reference voltages, comprising:
- a resistor ladder, having a first end and a second end coupled to respective first and second sources of reference potential, and having a plurality of serially connected resistors, each having first and second terminals and a resistance defined therebetween;
- variable resistance means, coupled to one resistor of the serially connected resistors, for changing the resistance thereof responsive to a control signal;
- comparison means, coupled to the one resistor, for generating a difference signal representing a difference between a predetermined reference potential and a potential measured between the first and second terminals of the one resistor;
- and
- control means, responsive to the difference signal for generating the control signal for the variable resistance means, said control signal changing the resistance of the one resistor in a sense to reduce the difference signal in magnitude.
An analog to digital converter (ADC) comprising:
- a voltage reference source which provides a plurality of voltage reference values, the voltage reference source including:
- a resistor ladder, having a first end and a second end coupled to respective first and second sources of reference potential, and having a plurality of serially connected resistors, each having first and second terminals and a resistance defined therebetween, for providing a respective plurality of reference voltage values;
- and
- autocalibration means, coupled to each of the plurality of resistors including:
- means for selecting one of the plurality of resistors;
- sampling means for measuring first and second ones of the plurality of reference voltage values provided at the first and second terminals of the selected resistor, respectively;
- difference means for generating a value representing a difference between the first and second reference voltage values;
- comparison means for comparing the generated difference value to a predetermined reference value to generate a control signal;
- and
- control means, coupled to the selected resistor and responsive to the control signal, for changing the resistance defined between the first and second terminals in a sense to match the difference value to the predetermined reference value;
- and
- means for comparing an input analog value to an analog signal derived from the plurality of reference voltage values to generate a digital value representing the input analog value.
Dependencies are inferred from the claim text.