Temperature sensor for image sensors
View Patent ↗An integrated temperature sensor provides an output current proportional to temperature rising from a zero value at a selectable reference temperature. The reference temperature can be selected by varying resistive values in the sensor's circuit. The temperature sensor can be manufactured at low cost and fully integrated on a chip using CMOS technology, and may be used for low-power applications.
1. A temperature sensor, comprising:
a first output transistor having first and second conduction terminals, the first conduction terminal coupled to a first voltage supply so that the first output transistor is configured to generate a first current proportional to absolute temperature from the second conduction terminal;
a current source coupled to the second conduction terminal and configured to draw a constant reference current from the second conduction terminal; and
an output terminal coupled to the second conduction terminal and configured to output an output current proportional to the absolute temperature for temperatures in excess of a first reference temperature;
wherein the value of the constant reference current determines a zero-crossing value of the output current.
2. The circuit of claim 1 , wherein the zero-crossing value of the output current is at the first reference temperature.
3. The circuit of claim 1 , further comprising a first resistive value in a temperature-sensing circuit coupled to the first output transistor and a second resistive value in the current source that adjust the zero-crossing value to be at a second reference temperature.
4. The circuit of claim 1 , wherein the constant reference current is independent of temperature of the temperature-sensing circuit.
5. The circuit of claim 1 , wherein the constant reference current varies less than about 5 microamps over a temperature range of about 200 Celsius for the temperature-sensing circuit.
6. The circuit of claim 1 , wherein the zero-crossing value corresponds to a selected reference temperature.
7. The circuit of claim 1 , further comprising a temperature-sensing circuit wherein a control terminal of the first output transistor is coupled to the temperature-sensing circuit.
8. The circuit of claim 7 , wherein the temperature-sensing circuit comprises:
a first circuit branch configured to couple between a first voltage supply and a second voltage supply;
a second transistor of a first type in the first circuit branch;
a third transistor of a second type coupled in series with the second transistor;
a first bipolar junction transistor coupled in series with the third transistor;
a second circuit branch configured to couple between the first voltage supply and the second voltage supply;
a fourth transistor of the first type in the second circuit branch and configured in a current mirror relationship with the second transistor;
a fifth transistor of the second type in series with the fourth transistor and configured in a current mirror relationship with the third transistor;
a resistor in series with the fifth transistor; and
a second bipolar junction transistor coupled in series with the resistor and configured in a current mirror relationship with the first bipolar junction transistor.
9. The circuit of claim 8 , wherein a control terminal of the second transistor is coupled to a control terminal of the first output transistor, and the conduction terminal of the first output transistor is coupled to the first supply voltage.
10. The circuit of claim 8 , wherein a control terminal of the fifth transistor is coupled to provide a temperature-dependent current in the current source.
11. The circuit of claim 8 , wherein the second bipolar junction transistor is configured to exhibit a higher current density flow than the first bipolar junction transistor.
12. The circuit of claim 11 , wherein the higher current density flow is by a factor of about 8.
13. The circuit of claim 1 , wherein the current source is configured to combine a second current proportional to absolute temperature with a temperature-dependent current to provide the constant reference current.
14. The circuit of claim 13 , wherein the current source comprises:
a first circuit branch configured to couple between a first voltage supply and a second voltage supply;
a second transistor of a first type in the first circuit branch;
a third transistor of a second type coupled in series with the second transistor;
a resistor in series with the third transistor;
a second circuit branch configured to couple between the first voltage supply and the second voltage supply;
a fourth transistor of the first type in the second circuit branch and configured in a current mirror relationship with the second transistor; and
a fifth transistor of the second type in series with the fourth transistor.
15. The circuit of claim 13 , wherein the second current proportional to absolute temperature is added to the second circuit branch by a sixth transistor having a control terminal coupled to a first output of a temperature-sensing circuit, and the temperature-dependent current is provided in the first circuit branch by the third transistor having a control terminal coupled to a second output of the temperature-sensing circuit.
16. The circuit of claim 15 , wherein the temperature-dependent current has an opposite dependence on temperature than the second current proportional to absolute temperature.
17. The circuit of claim 16 , further comprising a seventh transistor of the second type coupled in series with the first output and configured in a current mirror relationship with the fifth transistor.
18. A method for providing an output current proportional to temperature, the method comprising:
supplying a first current proportional to absolute temperature to a node of a temperature sensor;
removing a constant reference current from the node; and
outputting a second current proportional to absolute temperature from the node when temperature exceeds a first reference temperature;
wherein the value of the constant reference current determines a zero-crossing value of the second current.
19. The method of claim 18 , wherein the constant reference current is selected to determine a zero-crossing value of the second current.
20. The method of claim 18 , wherein the supplying comprises providing a first control signal from a first output of a temperature-sensing circuit to a control terminal of a first transistor to control the first transistor to supply the first current proportional to absolute temperature.
21. The method of claim 20 , wherein the removing comprises providing a second control signal from a current source to control terminal of a second transistor coupled in series with the first transistor.
22. The method of claim 21 , further comprising:
providing a third control signal to the current source from a second output of the temperature-sensing circuit; and
combining, in the current source, the second current proportional to absolute temperature with a temperature-dependent current to provide the constant reference current.
23. The method of claim 22 , wherein the temperature-dependent current has an opposite temperature dependence than the second current proportional to absolute temperature.
24. The method of claim 20 , wherein a zero-crossing value of the output current is determined by a first resistive value in the temperature-sensing circuit and a second resistive value in the current source.
25. The method of claim 20 , further comprising:
flowing a second current in a first circuit branch of the temperature-sensing circuit, wherein the first circuit branch comprises:
a second transistor of a first type;
a third transistor of a second type coupled in series with the second transistor; and
a first bipolar junction transistor coupled in series with the third transistor; and
flowing a third current in a second circuit branch of the temperature-sensing circuit, wherein the second circuit branch comprises:
a fourth transistor of the first type in a current mirror relationship with the second transistor;
a fifth transistor of the second type in series with the fourth transistor and configured in a current mirror relationship with the third transistor;
a resistor in series with the fifth transistor; and
a second bipolar junction transistor coupled in series with the resistor and configured in a current mirror relationship with the first bipolar junction transistor.
26. The method of claim 20 , wherein the constant reference current varies less than about 5 microamps over a temperature range of about 200 Celsius for the temperature-sensing circuit.
27. The method of claim 18 , further comprising:
flowing a second current in a first circuit branch of the current source, wherein the first circuit branch comprises:
a second transistor of a first type in the first circuit branch;
a third transistor of a second type coupled in series with the second transistor; and
a resistor in series with the third transistor; and
flowing a third current in a second circuit branch of the current source, wherein the second circuit branch comprises:
a fourth transistor of the first type in the second circuit branch and configured in a current mirror relationship with the second transistor; and
a fifth transistor of the second type in series with the fourth transistor.
28. A method, comprising:
generating a first current proportional to absolute temperature and containing temperature variant and temperature invariant portions;
generating a second current inverse to the first current and having temperature variant and temperature invariant portions;
summing the first current and the second current so as to generate a third current that is temperature invariant;
generating an output current that is temperature variant by subtracting the third current from the first current;
wherein the value of the third current determines a zero-crossing value of the first current.
29. The method of claim 28 , wherein the first current being greater than the third current indicates that the absolute temperature is above a threshold temperature.