Calibration of temperature sensing circuitry in an electronic device

• US 8,182,139 B2
• Filed: 05/30/2008
• Issued: 05/22/2012
• Est. Priority Date: 05/30/2008
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Fiennes, Hugo, Cox, Keith Alan
• Primary Examiner(s): VERBITSKY, GAIL KAPLAN
• Application Number:
  US12/130,650
• Publication Number:
  US 20090296769A1
• Time in Patent Office: 1,453 Days
• Field of Search: 374/100, 374/1, 374/163, 374/183, 374/185, 374170-173, 702130-136, 702/99, 327512-513
• US Class Current: 374/1
• CPC Class Codes: G01K 15/00 Testing or calibrating of thermometers
• CPC Class Codes: G01K 15/005 Calibration
• CPC Class Codes: G01K 7/425 Thermal management of integrated systems

Abstract

Temperature sensing circuitry is used for thermal management of an electronic device. The temperature sensing circuitry includes at least one thermistor placed at or near a component of the electronic device. The temperature sensing circuitry also includes a high-precision resistor for calibration purposes. The resistance of the resistor is equivalent to the resistance of the thermistor at a reference temperature. A calibration reading is obtained using a set current that is being passed through the resistor. An error present in the temperature sensing circuitry is determined based on the calibration reading and a design value. A temperature measurement associated with the component is then made using the thermistor, while the set current is being passed through the thermistor. The error is corrected in the temperature measurement of the component. Other embodiments are also described.

Claims

1. A method for thermal management in an electronic device, comprising:

obtaining a calibration reading using a set current that is being passed through a resistor in a temperature sensing circuit, wherein the temperature sensing circuit includes a thermistor which is placed at or near a component of the electronic device and the resistance of the resistor is equivalent to the resistance of the thermistor at a reference temperature;

determining an error present in the temperature sensing circuit based on the calibration reading and a design value; and

correcting for the error in a temperature measurement associated with the component, wherein the measurement is made using the thermistor while the set current is being passed through the thermistor.

2. The method of claim 1, wherein determining an error present in the temperature sensing circuit further comprises:

determining error in an analog-to-digital converter (ADC) and a current generator in the temperature sensing circuit, wherein the current generator provides the set current.

3. The method of claim 1, wherein the design value is based on a manufacture or design specification of an ADC, a current source, and the resistor in the temperature sensing circuit.

4. The method of claim 1, wherein the resistor is more accurate than the thermistor.

5. The method of claim 1, wherein the resistor is accurate to within +/−

0.1% or better, and the thermistor is accurate to within +/−

1% or better.

6. An apparatus for thermal management in an electronic device, the apparatus comprising:

means for providing a set current;

means for alternately passing the set current through a resistor and a thermistor wherein the resistance of the resistor equivalent to the resistance of the thermistor at a reference temperature;

means for obtaining a digital calibration reading while the set current is being passed through the resistor;

means for obtaining digital thermistor reading while the set current is being passed through the thermistor;

means for computing an error based on the digital calibration reading and a design value; and

means for providing a corrected temperature measurement, based on the computed error and the digital thermistor reading.

7. An apparatus for thermal management in an electronic device, comprising:

a current generator to provide a set current;

a multiplexer having an input coupled to receive the set current;

a thermistor coupled to an output of the multiplexer;

a resistor coupled to another output of the multiplexer, the resistor having a resistance that is equivalent to a resistance of the thermistor at a reference temperature;

an analog-to-digital converter (ADC) coupled to the input of the multiplexer, to obtain a digital thermistor voltage using the thermistor while the set current is being passed through the thermistor and a digital calibration reading using the resistor while the set current is being passed through the resistor;

a processing circuit to receive the thermistor voltage and the calibration reading, compute an error based on the calibration reading and a design value, and correct a temperature measurement based on the error and the thermistor voltage.

8. The apparatus of claim 7, wherein the processing circuit is to correct a temperature measurement by converting a corrected voltage measurement into a temperature value.

9. The apparatus of claim 7, wherein the design value is based on a manufacture or design specification of the ADC, the current generator, and the resistor.

10. The apparatus of claim 7, wherein the resistor is more accurate than the thermistor.

11. A method for thermal management in an electronic device, comprising:

obtaining a digitized resistor voltage while a set current provided by a current source is being passed through a resistor in a temperature sensing circuit, wherein the temperature sensing circuit includes a thermistor which is placed at or near a component of the electronic device and the resistance of the resistor is equivalent to the resistance of the thermistor at a reference temperature;

computing an error present in the temperature sensing circuit based on the digitized resistor voltage and a design value;

obtaining a digitized thermistor voltage while the set current provided by the current source is being passed through the thermistor; and

correcting a temperature measurement associated the component, based on the computed error and the digitized thermistor voltage.

12. The method of claim 11, wherein correcting comprises converting a corrected voltage measurement into a temperature value.

13. The method of claim 11, wherein the design value is based on a manufacture or design specification of an ADC that was used for obtaining the digitized resistor and thermistor voltages, the current source, and the resistor in the temperature sensing circuit.

14. The method of claim 11, wherein the resistor is more accurate than the thermistor.