CMOS temperature-to-digital converter with digital correction

• US 20080095213A1
• Filed: 10/21/2006
• Published: 04/24/2008
• Est. Priority Date: 10/21/2006
• Status: Active Grant

• Current Assignee: Intersil Americas LLC (Renesas Electronics Corporation)
• Original Assignee: Intersil Americas LLC (Renesas Electronics Corporation)
• Inventors: Benzel, Phillip J., Lin, Xijian
• Granted Patent: US 7,686,508 B2
• Time in Patent Office: Days
• US Class Current: 374/170
• CPC Class Codes: G01K 2219/00 Thermometers with dedicated analog to digital converters
• CPC Class Codes: G01K 7/015 using microstructures, e.g. made of silicon

Abstract

Methods and systems for producing a digital temperature reading are provided. In an embodiment, one or more current sources and one or more switches are used to selectively provide a first amount of current (I1) and a second amount of current (I2) to the emitter of a transistor (Q1), during different time slots of a time period, to thereby produce a first base-emitter voltage (Vbe1) and a second base-emitter voltage (Vbe2), where I1=I2*M, and M is a known constant. An analog-to-digital converter (ADC) digitizes analog signals representative of the magnitudes Vbe1 and Vbe2. A difference is determined between the magnitudes of Vbe1 and Vbe2. A digital calculator produces a digital temperature reading (DTR) based on the difference between the magnitudes of Vbe1 and Vbe2.

Claims

1. A method for producing a temperature reading, comprising:

(a) providing a transistor (Q1) including a base, an emitter and a collector, where the base is connected to the collector, and the collector is connected to ground;

(b) providing a first amount of current (I1) and a second amount of current (I2) to the emitter of the transistor (Q1), during different time slots of a time period, to thereby produce a first base-emitter voltage (Vbe1) and a second base-emitter voltage (Vbe2), where I1=I2*M, and M is a known constant;

(c) digitizing analog signals indicative of magnitudes of Vbe1 and Vbe2;

(d) digitally determining a difference between the magnitudes of Vbe1 and Vbe2; and

(e) producing a digital temperature reading (DTR) based on the difference between the magnitudes of Vbe1 and Vbe2.

2. The method of claim 1, wherein step (e) comprises producing the DTR using the following equation:

DTR=K*Data/[K*Data/(2̂

N)+1]

where K is a constant, Data is an N-bit digital value indicative of the difference between the magnitude of Vbe1 and the magnitude of Vbe2, and N is the number of bits of the Data, which is an integer ≧

2.

3. The method of claim 1, wherein I1 is produced during a first contiguous time slot, and I2 is produced during a second contiguous time slot the follows the first time slot.

4. The method of claim 1, wherein I1 is produced during one or more time slots that need not be contiguous, and I2 is produced during one or more further time slots that need not be contiguous.

5. The method of claim 1, wherein I1 is produced by simultaneously and continually turning on M current sources during a first time slot, and I2 is produced by separately turning on each of the M current sources during different portions of a second time slot that equals the first time slot.

6. The method of claim 5, wherein each of the different portions of the second time slot is equal to 1/M^th of the first time slot.

7. The method of claim 1, wherein I1 is produced by continually turning on a current source during a first time slot, and I2 is produced by turning on the same current source for only 1/M^th of a second time slot that equals the first time slot.

8. The method of claim 1, wherein step (d) includes using a digital up/down counter to determine a different between the magnitudes of Vbe1 and Vbe2.

9. The method of claim 1, wherein step (d) includes converting Vbe1 and Vbe2 to currents using a voltage-to-current converter that includes a first resistor (R1), to thereby produce the analog signals indicative of the magnitudes of Vbe1 and Vbe2.

10. The method of claim 9, further comprising:

providing a further transistor (Q3) including a base, an emitter and a collector, where the base is connected to the collector, and the collector is connected to ground;

providing a current proportional to absolute temperature (Iptat) to the emitter of the further transistor (Q3), to thereby produce a third base-emitter voltage (Vbe3); and

converting Vbe3 to a reference current (Iref) using a further voltage-to-current converter that includes a second resistor (R2), where Iref=Vbe3/R2;

wherein step (c) includes using Iref as a reference when digitizing the analog signals indicative of the magnitudes of Vbe1 and Vbe2; and

wherein step (f) comprises producing the DTR using the following equation

DTR=K*(R2/R1)*(kT/q)ln(M)/[K*(R2/R1)*(kT/q)ln(M)+Vbe3]*(2̂

N),

where K is a constant, k is Botzmann'"'"'s constant, T is the temperature in degrees Kelvin, q is the electron charge, and N is an integer ≧

2.

11. The method of claim 9, further comprising:

using one or more current sources and one or more switches to provide the first amount of current (I1) and the second amount of current (I2) to the emitter of the transistor (Q1), wherein the one or more switches are turned on and off at times that corresponds to transitions of a clock signal;

using a voltage-to-current converter is to convert Vbe1 and Vbe2 to currents; and

turning off a further switch, at the output of the voltage-to-current converter, for short time periods centered about transitions of the clock signal, to reduce effects of charge-injection due to the turning on and off of the one or more switches used to provide I1 and I2 to the emitter of the transistor (Q1).

12. The method of claim 1, further comprising:

providing a current proportion to absolute temperature (Iptat) to the emitter of the transistor (Q1) to thereby produce a third base-emitter voltage (Vbe3);

wherein step (f) comprises producing the DTR using the following equation

DTR=K*(kT/q)ln(M)/[K*(kT/q)ln(M)+Vbe3]*(2̂

N),

where K is a constant, k is Botzmann'"'"'s constant, T is the temperature in degrees Kelvin, q is the electron charge, and N is an integer ≧

2.

13. The method of claim 1, wherein the transistor (Q1) was produced using a bipolar junction transistor (BJT) process, a complementary-metal-oxide semiconductor (CMOS) process or a BJT/BiCMOS process.

14. A sensor system for producing a temperature reading, comprising:

a transistor (Q1) including a base, an emitter and a collector, where the base is connected to the collector, and the collector is connected to ground;

one or more current sources and one or more switches to selectively provide a first amount of current (I1) and a second amount of current (I2) to the emitter of the transistor (Q1), during different time slots of a time period, to thereby produce a first base-emitter voltage (Vbe1) and a second base-emitter voltage (Vbe2), where I1=I2*M, and M is a known constant;

an analog-to-digital converter (ADC) that digitizes analog signals representative of the magnitudes Vbe1 and Vbe2;

means for determining a difference between the magnitudes of Vbe1 and Vbe2;

a digital calculator to produce a digital temperature reading (DTR) based on the difference between the magnitudes of Vbe1 and Vbe2.

15. The system of claim 14, wherein the means for determining a difference between the magnitudes of Vbe1 and Vbe2 comprises an up/down counter.

16. The system of claim 15, wherein the up/down counter is part of the ADC.

17. The system of claim 14, wherein the ADC comprises a charge-balancing ADC.

18. The system of claim 14, wherein the ADC comprises a sigma-delta ADC.

19. The system of claim 14, wherein the digital calculator produces the DTR using the following equation:

DTR=K*Data/[K*Data/(2̂

N)+1]

where K is a constant, Data is an N-bit digital value indicative of the difference between the magnitude of Vbe1 and the magnitude of Vbe2, and N is an integer ≧

2.

20. The system of claim 14, further comprising:

a voltage-to-current converter, including a first resistor (R1), to produce the analog signals indicative of the magnitudes of Vbe1 and Vbe2.

21. The system of claim 20, further comprising:

a further transistor (Q3) including a base, an emitter and a collector, where the base is connected to the collector, and the collector is connected to ground;

a further current source to provide a current proportional to absolute temperature (Iptat) to the emitter of the further transistor (Q3), to thereby produce a third base-emitter voltage (Vbe3); and

a further voltage-to-current converter, including a second resistor (R2), to convert Vbe3 to a reference current (Iref), where Iref=Vbe3/R2;

wherein Iref is provided as a reference to the ADC; and

wherein the digital calculator produces the DTR using the following equation;

DTR=K*(R2/R1)*(kT/q)ln(M)/[K*(R2/R1)*(kT/q)ln(M)+Vbe3]*(2̂

N), where

K is a constant, k is Botzmann'"'"'s constant, T is the temperature in degrees Kelvin, q is the electron charge, and N the number of bits of resolution of the ADC, which is an integer ≧

2.

22. The system of claim 21, further comprising:

a further switch, at the output of the voltage-to-current converter;

wherein the one or more current sources and one or more switches, that selectively provide a first amount of current (I1) and a second amount of current (I2) to the emitter of the transistor (Q1), are turned on and off at times that correspond to transitions of a clock signal; and

wherein the further switch, at the output of the voltage-to-current converter, is closed for short time periods centered about transitions of the clock signal, to reduce effects of charge-injection due to the turning on and off of the one or more switches.

23. The system of claim 14, wherein the transistor (Q1) was produced using a bipolar junction transistor (BJT) process, a complementary-metal-oxide semiconductor (CMOS) process or a BJT/BiCMOS process.

24. The system of claim 14, wherein a current proportion to absolute temperature (Iptat) is selectively provided to the emitter of the transistor (Q1) to thereby produce a third base-emitter voltage (Vbe3);

and

wherein the digital calculator produces the DTR using the following equation

DTR=K*(kT/q)ln(M)/[K*(kT/q)ln(M)+Vbe3]*(2̂

N),

where K is a constant, k is Botzmann'"'"'s constant, T is the temperature in degrees Kelvin, q is the electron charge, and N the number of bits of resolution of the ADC, which is an integer ≧

2.

25. A method for producing a temperature reading using a transistor (Q1) including a base, an emitter and a collector, where the base is connected to the collector, and the collector is connected to ground;

(a) providing a first amount of current (I1) and a second amount of current (I2) to the emitter of the transistor (Q1) to thereby produce a first base-emitter voltage (Vbe1) and a second base-emitter voltage (Vbe2), where I1=I2*M, and M is a known constant;

(b) digitizing analog signals indicative of magnitudes of Vbe1 and Vbe2;

(c) digitally determining a difference between the magnitudes of Vbe1 and Vbe2; and

(d) producing a digital temperature reading (DTR) based on the difference between the magnitudes of Vbe1 and Vbe2.

26. The method of claim 25, wherein step (d) comprises producing the DTR using the following equation:

DTR=K*Data/[K*Data/(2̂

N)+1]

where K is a constant, Data is an N-bit digital value indicative of the difference between the magnitude of Vbe1 and the magnitude of Vbe2, and N is the number of bits of the Data, which is an integer ≧

2.

27. The method of claim 25, wherein step (d) comprises producing the DTR using the following equation:

DTR=K*(R2/R1)*(kT/q)ln(M)/[K*(R2/R1)*(kT/q)ln(M)+Vbe3]*(2̂

N),

where

K is a constant,

k is Botzmann'"'"'s constant,

T is the temperature in degrees Kelvin,

q is the electron charge,

N is an integer ≧

2;

R1 is the value of a first resistor (R1) that is part of a voltage-to-current converter that is used to convert Vbe1 and Vbe2 to currents, which are the analog signals indicative of the magnitudes of Vbe1 and Vbe2;

Vbe3 is a third base-emitter voltage produced by providing a current proportional to absolute temperature (Iptat) to an emitter of the further transistor (Q3); and

R2 is the value of a second resistor (R2) that is part of a voltage-to-current converter that is used to convert Vbe3 to a reference current (Iref) that is used when digitizing the analog signals indicative of the magnitudes of Vbe1 and Vbe2.