Circuitry and techniques for resistor-based temperature sensing

• US 9,182,295 B1
• Filed: 09/07/2012
• Issued: 11/10/2015
• Est. Priority Date: 09/09/2011
• Status: Active Grant

• Current Assignee: SiTime Corporation (Megachips Corporation)
• Original Assignee: SiTime Corporation (Megachips Corporation)
• Inventors: Perrott, Michael H., Lee, Shungneng
• Primary Examiner(s): Verbitsky, Gail Kaplan
• Application Number:
  US13/607,603
• Time in Patent Office: 1,159 Days
• Field of Search: 374170-173, 374/178, 374/183, 374/185, 374/184, 374/163, 374/102, 374/1, 702/130, 702132-135, 702/99
• US Class Current: 1/1
• CPC Class Codes: G01K 2219/00 Thermometers with dedicated analog to digital converters
• CPC Class Codes: G01K 7/12 Arrangements with respect to the cold junction, e.g. preventing influence of temperature of surrounding air
• CPC Class Codes: G01K 7/16 using resistive elements resistive elements per se H01C, H01L
• CPC Class Codes: G01K 7/186 using microstructures
• CPC Class Codes: G01K 7/22 the element being a non-linear resistance, e.g. thermistor G01K7/26 takes precedence
• CPC Class Codes: G01K 7/226 using microstructures, e.g. silicon spreading resistance
• CPC Class Codes: G01K 7/34 using capacitative elements capacitors per se H01G
• CPC Class Codes: H03B 5/04 Modifications of generator to compensate for variations in physical values, e.g. power supply, load, temperature
• CPC Class Codes: H03B 5/30 with frequency-determining element being electromechanical resonator
• CPC Class Codes: H03H 9/02244 of microelectro-mechanical resonators
• CPC Class Codes: H03L 1/02 against variations of temperature only

Abstract

A temperature to digital converter circuitry to generate output data which is representative of one or more temperature dependent characteristics of a temperature sensitive device (for example, MEMS thermistor having a resistance that correlates to its temperature), the temperature to digital circuitry comprising a switched capacitor network to generate a effective reference resistance in response to a switching signal, a signal generator to generate the switching signal, wherein the switching signal has a switching frequency which is controlled, at least in part, via control data, comparator circuitry to generate error data using the effective reference resistance and the resistance of the temperature sensitive device, and converter circuitry to generate the output data which is representative of one or more temperature dependent characteristics of the temperature sensitive device.

Claims

1. A method of sensing temperature using a microelectromechanical system (MEMS) thermistor, the method comprising:

generating a switching signal having a variable and controllable switching frequency;

switchably enabling current to flow into and out of a switched capacitor network in response to the switching signal such that the switched capacitor network exhibits an effective resistance dependent upon the switching frequency;

comparing the effective resistance of the switched capacitor network and the resistance of the microelectromechanical system (MEMS) thermistor to generate error data;

generating data representing temperature of the MEMS thermistor using the error data; and

outputting the data representative of MEMS thermistor temperature.

2. The method of claim 1 wherein generating the switching signal having a variable and controllable switching frequency comprises varying the switching frequency of the switching signal as a function of temperature to adjust the effective resistance of the switched capacitor network in accordance with temperature-induced change in the resistance of the MEMS thermistor.

3. The method of claim 1 wherein generating the switching signal comprises varying the switching frequency as a function of temperature based, at least in part, on the error data.

4. The method of claim 1 further including converting the error data into a digital value.

5. The method of claim 4 further including processing the digital value to generate control data to adjust the switching frequency of the switching signal.

6. The method of claim 5 wherein the switching frequency of the switching signal is adjusted to adjust the effective resistance of the switched capacitor network so that effective reference of the switched capacitor network is substantially equal to the resistance of the temperature sensitive device.

7. The method of claim 1 wherein (i) the error data is representative of a difference between the effective resistance of the switched capacitor network and the resistance of the MEMS thermistor, (ii) the effective resistance of the switched capacitor network is dependent on the switching frequency of the switching signal, and (iii) the frequency of the switching signal is varied based at least in part on the data representative of MEMS thermistor temperature to form a feedback loop in which the effective resistance of the switched capacitor network is adjusted in a direction that lessens the difference between the effective resistance of the switched capacitor network and the resistance of the MEMS thermistor.

8. The method of claim 1 wherein generating the switching signal comprises varying the switching frequency of the switching signal based at least in part on the data representing temperature of the MEMS thermistor such that the switching frequency is temperature dependent.

9. The method of claim 1 wherein comparing the effective resistance of the switched capacitor network and the resistance of the MEMS thermistor to generate error data comprises generating error data indicative of a difference between the effective resistance of the switched capacitor network and the resistance of the MEMS thermistor.

10. A temperature sensor comprising:

a microelectromechanical system (MEMS) thermistor having a resistance that correlates to its temperature;

a switched capacitor network having one or more capacitors and circuitry to switchably enable current flow into and out of the one or more capacitors in response to a switching signal such that the switched capacitor network exhibits an effective resistance dependent upon the switching frequency of the switching signal;

a signal generator, coupled to the switched capacitor network, to generate the switching signal with variable and controllable switching frequency;

comparator circuitry, coupled to the switched capacitor network and the MEMS thermistor, to generate error data using (i) the effective resistance of the switched capacitor network and (ii) the resistance of the MEMS thermistor; and

converter circuitry, coupled to the signal generator and the comparator circuitry, to generate output data which is representative of the temperature of the MEMS thermistor using the error data.

11. The temperature sensor of claim 10 wherein the switched capacitor network and MEMS thermistor are coupled in series between upper and lower voltage supply nodes to form a voltage divider, and wherein the comparator circuitry comprises circuitry to detect a change in voltage output by the voltage divider.

12. The temperature sensor of claim 10 wherein the converter circuitry includes an analog to digital converter circuitry having a voltage-controlled oscillator.

13. The temperature sensor of claim 10 wherein the signal generator includes a frequency divider, coupled to the switched capacitor network and responsive to the error data, to generate the switching signal.

14. The temperature sensor of claim 13 wherein the signal generator further comprises a Sigma-Delta modulator, coupled to the frequency divider, to control the switching frequency of the switching signal.

15. The temperature sensor of claim 14 wherein the signal generator further comprises logic circuitry to generate a control value based at least in part on the output data generated by the converter circuitry, and to output the control value to the Sigma-Delta modulator, the Sigma-Delta modulator including circuitry to generate data applied within the frequency divider based, at least in part, on the control value.

16. The temperature sensor of claim 10 wherein the signal generator to generate the switching signal comprises circuitry to vary the switching frequency of the switching signal based at least in part on the output data such that the switching frequency is temperature dependent.

17. The temperature sensor of claim 10 wherein the comparator circuitry to generate error data comprises circuitry to generate error data indicative of a difference between the effective resistance of the switched capacitor network and the resistance of the MEMS thermistor.

18. The temperature sensor of claim 10 wherein the signal generator additionally generates one or more comparator control pulses at the switching frequency of the switching signal, and wherein the comparator applies one or more control pulses to generate, as the error data, a time-varying signal representative of a time-varying difference between the effective resistance of the switched capacitor network and the resistance of the MEMS thermistor.

19. The temperature sensor of claim 10 wherein (i) the error data is representative of a difference between the effective resistance of the switched capacitor network and the resistance of the MEMS thermistor, (ii) the effective resistance of the switched capacitor network is dependent on the switching frequency of the switching signal generated by the signal generator, and (iii) the signal generator is coupled to receive the output data from the converter circuitry and includes circuitry to vary the frequency of the switching signal based at least in part on the output data to form a feedback loop in which the effective resistance of the switched capacitor network is adjusted in a direction that lessens the difference between the effective resistance of the switched capacitor network and the resistance of the MEMS thermistor.