Linearized temperature sensor

• US 6,183,131 B1
• Filed: 03/30/1999
• Issued: 02/06/2001
• Est. Priority Date: 03/30/1999
• Status: Expired due to Term

• Current Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Original Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Inventors: Subrahmayan, Ravi, Sheehan, Gary S., Holloway, Peter R.
• Primary Examiner(s): Bennett, G. Bradley
• Assistant Examiner(s): VERBITSKY, GAIL KAPLAN
• Application Number:
  US09/281,637
• Time in Patent Office: 679 Days
• Field of Search: 327/512, 374/163, 374/170, 374/171, 374/172, 374/178, 374/180
• US Class Current: 374/172
• CPC Class Codes: G01K 7/21 for modifying the output characteristic, e.g. linearising

Abstract

A temperature sensor corrects the parabolic curvature error in the output signal without attempting to linearize the reference voltage itself. A temperature sensor produces a temperature output signal that is a function of the ratio of a temperature dependent voltage to a reference voltage. The temperature sensor uses a nonlinear reference voltage, e.g., the reference voltage conforms to a curve with an approximately hyperbolic shape over a temperature range, so that the ratio of the temperature dependent voltage to the hyperbolic reference voltage will be linear. The hyperbolic reference voltage is generated by summing a reference voltage with an appropriate temperature dependent voltage. The “gain” or slope of the ratio is altered by adjusting a scaling factor. Finally, the offset of the ratio is adjusted so that the temperature sensor produces the appropriate output signal at ambient temperature. Thus, despite the present of curvature in the reference voltage of the temperature sensor, a highly linear and accurate temperature sensor may be constructed using the hyperbolic linearization technique without requiring complex or expensive reference voltage correction circuits.

Claims

1. A temperature sensor comprising:

a reference voltage circuit producing a reference voltage;

a thermometer circuit producing a temperature dependent correction voltage;

a first summing circuit coupled to said reference voltage circuit and said thermometer circuit, said first summing circuit producing a voltage output signal that is the sum of said correction voltage and said reference voltage;

a normalizing circuit receiving said voltage output signal and a temperature dependent voltage;

an amplifier circuit coupled to said normalizing circuit, said amplifying circuit producing a scaling factor, wherein said normalizing circuit produces a temperature output signal by generating a ratio of said temperature dependent voltage and said voltage output signal multiplied by said scaling factor; and

a second summing circuit coupled to said normalizing circuit and receiving said temperature output signal, said second summing circuit summing said temperature output signal with a temperature offset correction factor to generate a corrected temperature output signal.

2. The temperature sensor of claim 1, wherein said voltage output signal generated by said first summing circuit has a nonlinear curvature.

3. The temperature sensor of claim 2, wherein said nonlinear curvature is an approximately hyperbolic curvature.

4. The temperature sensor of claim 1, wherein said amplifier circuit is disposed between said first summing circuit and said normalizing circuit.

5. The temperature sensor of claim 1, wherein said amplifier circuit is disposed between said thermometer circuit and said normalizing circuit.

6. The temperature sensor of claim 1, wherein said normalizing circuit is an analog to digital converter circuit, said analog to digital converter circuit producing a digital temperature output signal.

7. The temperature sensor of claim 1, wherein said normalizing circuit receives said temperature dependent voltage from said thermometer circuit.

8. The temperature sensor of claim 1, further comprising a second thermometer circuit, wherein said normalizing circuit receives said temperature dependent voltage from said second thermometer circuit.

9. The temperature sensor of claim 1, wherein said voltage reference circuit is a bandgap voltage reference circuit.

10. The temperature sensor of claim 7, wherein said thermometer circuit is a proportional to absolute temperature circuit.

11. A method of generating a temperature output signal, said method comprising:

providing a first reference voltage;

providing a temperature dependent correction voltage;

summing said reference voltage and said correction voltage together to produce a second reference voltage;

providing a temperature dependent voltage; and

normalizing said temperature dependent voltage as a ratio of said temperature dependent voltage and said second reference voltage to generate a temperature output signal.

12. The method of claim 11, further comprising:

providing a scaling factor, wherein said temperature output signal includes said scaling factor; and

offsetting said temperature output signal by a temperature correction offset factor to generate a corrected temperature output signal.

13. The method of claim 12, wherein said corrected temperature output signal is a digital corrected temperature output signal.

14. The method of claim 11, wherein said second reference voltage has a nonlinear curvature over the operating range of temperatures.

15. The method of claim 14, wherein said nonlinear curvature is an approximately hyperbolic curvature over the operating range of temperatures.

16. The method of claim 14, wherein said second reference voltage has a peak value at a temperature other than ambient temperature.

17. The method of claim 14, wherein said second reference voltage has a peak value at a temperature T₀ defined by:

$T_0=\left(T_{\mathrm{CAL}}\right)<br><br>\text{\hspace{1em}<br><br>}<br><br>\exp <br><br>\text{\hspace{1em}<br><br>}\left[\frac{V_{\mathrm{GO}}+\mathrm{\gamma <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>T_{\mathrm{CAL}}}{2<br><br>V_{\mathrm{GO}}+\mathrm{\gamma <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>T_{\mathrm{CAL}}}\right];<br><br>\mathrm{where}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\gamma <br><br>}\equiv <br><br>\frac{k}{q}<br><br>\left[4-\mathrm{\alpha <br><br>}-\mathrm{\eta <br><br>}\right]$

where T_CAL is the calibration temperature, V_GO is the bandgap voltage, γ

is a combined process, device, and operating current temperature coefficient variable, α and

η

are device dependent parameters.

18. The method of claim 12, wherein said scaling factor when multiplied by said temperature dependent voltage is described by:

$C<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\beta <br><br>}}_{\mathrm{CAL}}=\frac{4<br><br>{\left(V_{\mathrm{GO}}+\mathrm{\gamma <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>T_{\mathrm{CAL}}\right)}^3}{{\left(2<br><br>V_{\mathrm{GO}}+\mathrm{\gamma <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>T_{\mathrm{CAL}}\right)}^2}$

where T_CAL is the calibration temperature, C is the scaling factor, β

_CAL is temperature dependent voltage at the calibration temperature, V_GO is the bandgap voltage, and γ

is a combined process, device, and operating current temperature coefficient variable.

19. The method of claim 12, wherein said temperature correction offset factor is described by:

$K=\frac{{\mathrm{\gamma <br><br>}<br><br>\left(T_{\mathrm{CAL}}\right)}^2}{2<br><br>V_{\mathrm{GO}}+\mathrm{\gamma <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>T_{\mathrm{CAL}}}$

where K is the temperature offset correction factor, T_CAL is the calibration temperature, V_GO is the bandgap voltage, and γ

is a combined process, device, and operating current temperature coefficient variable.

20. The method of claim 12, wherein said corrected temperature output signal is described by a transfer function according to the following:

$H<br><br>\left(T\right)=\begin{array}{c}\frac{4<br><br>{T<br><br>\left(V_{\mathrm{GO}}+\mathrm{\gamma <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>T_{\mathrm{CAL}}\right)}^3}{{\left(2<br><br>V_{\mathrm{GO}}+\mathrm{\gamma <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>T_{\mathrm{CAL}}\right)}^2<br><br>\left[V_{\mathrm{GO}}+\mathrm{\gamma <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>T<br><br>\left(1+\left(\frac{V_{\mathrm{GO}}+\mathrm{\gamma <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>T_{\mathrm{CAL}}}{2<br><br>\text{\hspace{1em}<br><br>}<br><br>V_{\mathrm{GO}}+\mathrm{\gamma <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>T_{\mathrm{CAL}}}\right)+\ln <br><br>\frac{T_{\mathrm{CAL}}}{T}\right)\right]}+\end{array}<br><br>\frac{{\mathrm{\gamma <br><br>}<br><br>\left(T_{\mathrm{CAL}}\right)}^2}{2<br><br>V_{\mathrm{GO}}+\mathrm{\gamma <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>T_{\mathrm{CAL}}}.$

where T is temperature, T_CAL is the calibration temperature, V_GO is the bandgap voltage, and γ

is a combined process, device, and operating current temperature coefficient variable.

21. A temperature sensor comprising:

means for generating a reference voltage having a nonlinear curvature over a temperature range;

means for scaling said reference voltage having a nonlinear curvature to generate a scaled nonlinear reference voltage;

means for generating a temperature dependent voltage;

means for normalizing said temperature dependent voltage with the scaled nonlinear reference voltage to generate a temperature output signal; and

means for adding a constant temperature offset to said temperature output signal to generate a corrected temperature output signal.

22. The temperature sensor of claim 21, wherein said reference voltage having a nonlinear curvature has an approximately hyperbolic curvature.

23. The temperature sensor of claim 21, wherein said means for generating a reference voltage having a nonlinear curvature comprises:

means for generating a reference voltage having a parabolic curvature error over said temperature range;

means for generating a temperature dependent correction voltage; and

means for adding said temperature dependent correction voltage to said reference voltage having a parabolic curvature error.

24. The temperature sensor of claim 23, wherein said means for generating a reference voltage is a bandgap voltage reference circuit, said means for generating a temperature dependent correction voltage is a proportional-to-absolute-temperature voltage circuit, and said means for adding is a summing circuit.

25. The temperature sensor of claim 21, wherein said means for scaling said reference voltage is an amplifier circuit, said means for generating a temperature dependent voltage is a proportional-to-absolute-temperature voltage circuit, said means for normalizing is an analog to digital converter circuit, and said means for adding is a summing circuit.