Temperature measurement using a thermistor
AssigneeCirrus Logic, Inc.
InventorsVamsikrishna Parupalli, Zhong You, Johann G. Gaboriau, Amar Vellanki, Vikrant Arumugam
Life of this patent
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Abstract
A current digital-to-analog converter may be used in a system for measuring temperature of a thermistor, with mismatch reduction techniques applied to digital-to-analog converter elements of the digital-to-analog converter in order to maximize accuracy and precisions of the temperature measurement.
Claims18
A system comprising:
- a digital-to-analog converter (DAC) comprising a plurality of DAC elements;
- an analog-to-digital converter (ADC) path;
- a thermistor coupled between an output of the DAC and an input of the ADC path;
- a reference impedance coupled in parallel with the thermistor between the output of the DAC and the input of the ADC path;
- and
- a digital controller coupled between an output of the ADC path and an input of the DAC and configured to:
- cause the DAC to drive a test current into the thermistor;
- measure a test voltage across the thermistor responsive to the test current via the ADC path;
- determine a first current for maximizing an input signal to the ADC based on the test voltage;
- enable a first number of the DAC elements of the DAC in order to generate the first current and drive the first current into the thermistor;
- measure a first voltage across the thermistor responsive to the first current via the ADC path;
- while measuring the first voltage, cause the plurality of DAC elements to be equally engaged via a mismatch reduction technique;
- determine a second current based on an impedance of the reference impedance;
- enable a second number of the DAC elements of the DAC in order to generate the second current and drive the second current into the reference impedance;
- measure a second voltage across the reference impedance responsive to the second current via the ADC path;
- while measuring the second voltage, cause the plurality of DAC elements to be equally engaged via the mismatch reduction technique;
- and
- determine an impedance of the thermistor based on the first voltage and the second voltage.
A method comprising, in a system having a digital-to-analog converter (DAC) comprising a plurality of DAC elements, an analog-to-digital converter (ADC) path, a thermistor coupled between an output of the DAC and an input of the ADC path, and a reference impedance coupled in parallel with the thermistor between the output of the DAC and the input of the ADC path:
- controlling the system with a digital controller coupled between an output of the ADC path and an input of the DAC and configured to:
- cause the DAC to drive a test current into the thermistor;
- measure a test voltage across the thermistor responsive to the test current via the ADC path;
- determine a first current for maximizing an input signal to the ADC based on the test voltage;
- enable a first number of the DAC elements of the DAC in order to generate the first current and drive the first current into the thermistor;
- measure a first voltage across the thermistor responsive to the first current via the ADC path;
- while measuring the first voltage, cause the plurality of DAC elements to be equally engaged via a mismatch reduction technique;
- determine a second current based on an impedance of the reference impedance;
- enable a second number of the DAC elements of the DAC in order to generate the second current and drive the second current into the reference impedance;
- measure a second voltage across the reference impedance responsive to the second current via the ADC path;
- while measuring the second voltage, cause the plurality of DAC elements to be equally engaged via the mismatch reduction technique;
- and
- determine an impedance of the thermistor based on the first voltage and the second voltage.
Dependencies are inferred from the claim text.