Temperature sensor with frequency-controlled reference

• US 10,175,119 B1
• Filed: 11/29/2016
• Issued: 01/08/2019
• 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): Kaplan Verbitsky, Gail
• Application Number:
  US15/364,179
• Time in Patent Office: 770 Days
• Field of Search: 374183, 374184, 374185, 374170-173, 374163
• 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

The temperature-dependent resistance of a MEMS structure is compared with an effective resistance of a switched CMOS capacitive element to implement a high performance temperature sensor.

Claims

1. A temperature sensor comprising:

a microelectromechanical-system (MEMS) structure having a resistance that varies with temperature;

a switched component network that exhibits an effective resistance according to the frequency of a switching signal;

circuitry to determine a difference between the resistance of the MEMS structure and the effective resistance of the switched component network; and

circuitry to generate a temperature output based at least in part on the difference between the resistance of the MEMS structure and the effective resistance of the switched component network.

2. The temperature sensor of claim 1 wherein the switched component network comprises a plurality of capacitive elements.

3. The temperature sensor of claim 1 wherein the circuitry to generate the temperature output comprises a signal generating circuit to generate the switching signal.

4. The temperature sensor of claim 3 wherein the signal generating circuit comprises a MEMS oscillator, distinct from the MEMS structure, to generate a reference clock signal and circuitry to cycle the switching signal between first and second signal levels at the switching signal frequency, the switching signal frequency being variable and dependent, at least in part, on the reference clock signal.

5. The temperature sensor of claim 1 wherein the circuitry to generate the temperature output comprises a signal generating circuit to generate, as the switching signal, at least first and second clock signals that cycle at the switching signal frequency and are phase offset from one another.

6. The temperature sensor of claim 1 wherein the switched component network exhibits a capacitance and wherein the circuitry to generate the temperature output comprises a signal generating circuit that cycles the switching signal at the switching signal frequency to develop a frequency-dependent voltage across the capacitance, the frequency-dependent voltage corresponding to the effective resistance of the switched component network.

7. The temperature sensor of claim 6 wherein the signal generating circuit receives a feedback signal from the circuitry that determines the difference between the resistance of the MEMS structure and the effective resistance of the switched component network.

8. The temperature sensor of claim 7 wherein the feedback signal is dependent, at least in part, on the difference between the resistance of the MEMS structure and the effective resistance of the switched component network, and wherein the signal generating circuit adjusts the switching signal frequency in response the feedback signal to form a feedback loop.

9. The temperature sensor of claim 8 wherein the signal generating circuit adjusts the switching signal frequency in a direction, toward a higher frequency or a lower frequency, that reduces the difference between the resistance of the MEMS structure and the effective resistance of the switched component network to implement a negative feedback loop.

10. The temperature sensor of claim 8 wherein the signal generating circuit adjusts the switching signal frequency by increasing or decreasing a digital control value, the circuitry to generate the temperature output comprising circuitry to generate, as a temperature output, a digital output value based, at least in part, on the digital control value.

11. A method of operation within a temperature sensor having a microelectromechanical-system (MEMS) structure, the method comprising:

generating, within a switched component network, an effective resistance according to the frequency of a switching signal;

determining a difference between a temperature-dependent resistance of the MEMS structure and the effective resistance of the switched component network; and

generating a temperature output based at least in part on the difference between the resistance of the MEMS structure and the effective resistance of the switched component network.

12. The method of claim 11 wherein generating the temperature output comprises generating the switching signal within a signal generating circuit that includes a MEMS oscillator, the MEMS oscillator being distinct from the MEMS structure.

13. The method of claim 12 wherein generating the switching signal within the signal generating circuit comprises enabling the MEMS oscillator to generate a reference clock signal and cycling the switching signal between first and second signal levels at the switching signal frequency, the switching signal frequency being variable and dependent, at least in part, on the reference clock signal.

14. The method of claim 12 wherein generating the switching signal comprises generating, as component signals of the switching signal, first and second clock signals that cycle at the switching signal frequency and are phase offset from one another.

15. The method of claim 11 wherein the switched component network comprises a plurality of passive components interconnected by switch elements and wherein generating the effective resistance within the switched component network comprises cycling the switch elements between conducting and non-conducting states.

16. The method of claim 11 wherein the switched component network exhibits a capacitance and wherein generating the effective resistance comprises cycling the switching signal at the switching signal frequency to develop a frequency-dependent voltage across the capacitance, the frequency-dependent voltage corresponding to the effective resistance.

17. The method of claim 16 wherein generating the temperature output based at least in part on the difference between the resistance of the MEMS structure and the effective resistance of the switched component network comprises generating a feedback signal based on the difference between the resistance of the MEMS structure and the effective resistance of the switched component network and wherein cycling the switching signal at the switching signal frequency to develop a frequency-dependent voltage across the capacitance comprises cycling the switching signal at a frequency determined, at least in part, by the feedback signal.

18. The method of claim 17 wherein cycling the switching signal at the frequency determined, at least in part, by the feedback signal comprises adjusting the switching signal frequency in a direction, toward a higher frequency or a lower frequency in accordance with the feedback signal, that reduces the difference between the resistance of the MEMS structure and the effective resistance of the switched component network.

19. The method of claim 18 wherein adjusting the switching signal frequency comprises increasing or decreasing a digital control value that controls the switching signal frequency, and wherein generating the temperature output comprises generating a digital output value representative of temperature based, at least in part, on the digital control value.

20. A temperature sensor comprising:

a microelectromechanical-system (MEMS) structure having a resistance that varies with temperature;

means for generating, within a switched component network, an effective resistance according to the frequency of a switching signal;

means for determining a difference between the resistance of the MEMS structure and the effective resistance of the switched component network; and

generating a temperature output based at least in part on the difference between the resistance of the MEMS structure and the effective resistance of the switched component network.