Accurate on-chip temperature sensing using thermal oscillator

1. A calibrated temperature sensor comprising:

a power on oscillator responsive to a calibration enable signal for providing a power on clock signal;

a temperature dependent oscillator responsive to said calibration enable signal for providing a temperature dependent clock signal; and

a measurement logic circuit for counting a first number of pulses of said temperature dependent clock signal during a first calibration period using said power on clock signal, a second number of pulses of said temperature dependent clock signal during a second calibration period using a system clock signal, a third number of pulses of said power on clock signal over a third calibration period using said system clock signal, and a fourth number of pulses of said temperature dependent clock signal using said system clock signal during a normal operation mode, wherein said first calibration period precedes both said second and said third calibration periods.

2. The calibrated temperature sensor of claim 1 , further comprising:

a power sniffer logic circuit having an input for receiving a power supply voltage, and an output for providing said calibration enable signal in response to said power supply voltage reaching a predetermined level.

3. The calibrated temperature sensor of claim 2 , wherein said power sniffer logic circuit comprises:

a power sniffer circuit having an input for receiving said power supply voltage, and an output for providing a power good signal when said power supply voltage exceeds a threshold; and

a latch that activates said calibration enable signal in response to an activation of said power good signal, and clears said calibration enable signal in response to an activation of a calibration done signal,

wherein said measurement logic circuit activates said calibration done signal in said normal operation mode.

4. The calibrated temperature sensor of claim 1 , wherein said power on oscillator comprises a ring oscillator.

5. The calibrated temperature sensor of claim 1 , wherein said temperature dependent oscillator comprises a ring oscillator.

6. The calibrated temperature sensor of claim 1 , wherein said temperature dependent oscillator further comprises a current-controlled ring oscillator.

7. The calibrated temperature sensor of claim 1 , wherein said measurement logic circuit comprises:

a first multiplexer having a first input for receiving said power on clock signal, a second input for receiving said temperature dependent clock signal, a control input for receiving said calibration enable signal, and an output;

a counter having an input coupled to said output of said first multiplexer, a control input for receiving an oscillator enable signal, and an output for providing a data signal representative of a number of clock pulses counted in a selected mode;

a second multiplexer having a first input for receiving said power on clock signal, a second input for receiving said system clock signal, a control input for receiving said calibration enable signal, and an output; and

a control logic circuit responsive to said output of said second multiplexer for providing said oscillator enable signal and said calibration done signal.

8. The calibrated temperature sensor of claim 1 , wherein said second calibration period precedes said third calibration period.

9. The calibrated temperature sensor of claim 1 , wherein said third calibration period precedes said second calibration period.

10. An integrated circuit comprising:

a functional unit for receiving a power supply voltage and performing a predetermined operation in a normal operation mode in response to said power supply voltage;

wherein said functional unit comprises a calibrated temperature sensor that operates using said power supply voltage and provides a temperature signal in a normal operation mode, said calibrated temperature sensor comprising:

a power on oscillator responsive to a calibration enable signal for providing a power on clock signal;

a temperature dependent oscillator responsive to said calibration enable signal for providing a temperature dependent clock signal; and

a measurement logic circuit for counting a first number of pulses of said temperature dependent clock signal during a first calibration period using said power on clock signal, a second number of pulses of said temperature dependent clock signal during a second calibration period using a system clock signal, a third number of pulses of said power on clock signal over a third calibration period using said system clock signal, and a fourth number of pulses of said temperature dependent clock signal using said system clock signal during a normal operation mode, wherein said first calibration period precedes both said second and third calibration periods.

11. The integrated circuit of claim 10 , wherein said power on oscillator comprises a ring oscillator.

12. The integrated circuit of claim 10 , wherein said temperature dependent oscillator comprises a ring oscillator.

13. The integrated circuit of claim 12 , wherein said temperature dependent oscillator further comprises a current-controlled ring oscillator.

14. The integrated circuit of claim 10 , wherein the integrated circuit is a data processor and the functional unit comprises one of a central processing unit core and a graphics processing unit (GPU) core.

15. The integrated circuit of claim 10 , further comprising:

a system management unit responsive to said first, second, third, and fourth numbers of pulses to determine a temperature in said normal operation mode and to make a power management decision in response to said temperature exceeding a temperature threshold.

16. A method comprising:

providing a power on clock signal in response to a calibration enable signal;

providing a temperature dependent clock signal using a temperature dependent oscillator in response to said calibration enable signal; and

counting a first number of pulses of said temperature dependent clock signal during a first calibration period using said power on clock signal;

counting a second number of pulses of said temperature dependent clock signal during a second calibration period using a system clock signal;

counting a third number of pulses of said power on clock signal over a third calibration period using said system clock signal, wherein said first calibration period precedes both said second and third calibration periods; and

counting a fourth number of pulses of said temperature dependent clock signal using said system clock signal during a normal operation mode.

17. The method claim 16 , wherein said counting said second number of pulses precedes said counting said third number of pulses.

18. The method claim 16 , wherein said counting said third number of pulses precedes said counting said second number of pulses.

19. The method of claim 16 , further comprising:

powering said temperature dependent oscillator with a power supply voltage during said normal operation mode; and

powering a functional unit thermally coupled to said temperature dependent oscillator with said power supply voltage during said normal operation mode.

20. The method of claim 16 , further comprising:

determining a temperature in said normal operation mode responsive to said first, second, third, and fourth numbers of pulses; and

making a power management decision in response to said temperature exceeding a temperature threshold.