Method and apparatus for calibrating a sensor
Described is a current-mode thermal sensor with calibration apparatus which comprises: a first transistor with a gate terminal coupled to a first node; a second transistor with a gate terminal coupled to a second node; a first resistor coupled to the first and second nodes; a second resistor coupled to the first node and a supply node; a diode coupled to the second node and the supply node; a third resistor coupled to the second node; and a switch coupled to the third resistor and a reference supply.
1. An apparatus comprising:
a first transistor with a gate terminal coupled to a first node and a current source;
a second transistor with a gate terminal coupled to a second node and ground;
a first resistor coupled to the first and second nodes;
a second resistor coupled to the first node and a reference voltage supply;
a diode coupled to the second node;
a third resistor coupled to the second node and the voltage reference supply; and
a switch coupled to the third resistor and the voltage reference supply, and wherein a temperature is sensed by subtracting a first current from the first resistor with a second current from the third resistor at the first node when the switch is on.
2. The apparatus of claim 1 , wherein the voltage reference supply is a power supply.
3. The apparatus of claim 1 , wherein the switch is operable to be closed or opened for calibrating the apparatus.
4. The apparatus of claim 1 , wherein the first and second transistors configured to operate in weak inversion mode.
5. The apparatus of claim 1 , wherein the first and second transistors are configured to form a differential pair.
6. The apparatus of claim 1 , wherein the first and second transistors are configured to provide a PTAT signal.
7. The apparatus of claim 1 , wherein the diode is configured to provide a CTAT signal on the first and second nodes.
8. The apparatus of claim 1 , wherein
the first current passes through the first resistor, and
the second current passes through the third transistor.
9. The apparatus of claim 8 , further comprising a current mirror wherein the second current is a mirror of current source.
10. The apparatus of claim 8 further comprises:
an amplifier including inputs coupled to nodes of the current mirror, and an output; and
a buffer including an input coupled to the output of the amplifier, and an output coupled to the first node.
11. The apparatus of claim 10 , wherein the buffer comprises devices that coupled together provide a non-linear characteristic.
12. The apparatus of claim 1 further comprises a circuit configured to adjust resistance of the second resistor.
13. The apparatus of claim 12 , wherein the circuit comprises a digital-to-analog converter (DAC).
14. A method for calibrating an apparatus, the method comprising:
determining a first digital code representing two unknown parameters by turning off a switch;
turning on the switch to couple a node to a known voltage reference to add known current to the node, the known current is subtracted from another current;
determining a second digital code representing the two unknown parameters when the switch is turned on using a result of the known current subtracted from another current;
computing a value of at least one of the unknown parameters using the known voltage, and the first and second digital code; and
calibrating the apparatus based on the computed value of at least one of the unknown parameters.
15. The method of claim 14 , wherein the at least one of the unknown parameters is temperature coefficient of a diode.
16. The method of claim 15 , wherein the first digital code is determined at an unknown temperature.
17. The method of claim 16 , wherein the known current is added at the same unknown temperature, and wherein the known current changes operating point of the apparatus.
18. The method of claim 14 further comprises storing the computed value of the unknown parameter in a storage unit.
19. The method of claim 18 further comprises trimming the apparatus by adjusting components of the apparatus by the stored computed value.
20. The method of claim 14 , wherein the apparatus comprises:
a first transistor with a gate terminal coupled to a first node and a current source;
a second transistor with a gate terminal coupled to a second node and ground;
a first resistor coupled to the first and second nodes;
a second resistor coupled to the first node and a reference voltage supply;
a diode coupled to the second node; and
a third resistor coupled to the second node and the voltage reference supply; and
wherein the switch is coupled to the third resistor and voltage reference supply and wherein a temperature is sensed by subtracting a first current form the first resistor with a second current from the third resistor at the first node when the switch is on.
21. A method comprising:
determining a first digital code representing ‘N’ number of unknown parameters;
coupling “N−1” number of different reference signals to a processing core by performing “N−1” separate measurement operations;
determining another “N−1” digital codes representing the ‘N’ unknown parameters by using a result of subtracting a known current with another current;
computing a value of at least one of the ‘N’ unknown parameters using the known “N−1” reference signals, and “N” number of digital codes; and
calibrating an apparatus, having the processing core, based on the computed value of the at least one of the ‘N’ unknown parameter, where ‘N’ is an integer.
22. The method of claim 21 , wherein the apparatus is a thermal sensor, and the processing core includes a node of the thermal sensor.
23. The method of claim 21 , wherein the ‘N’ unknown parameters include temperature and temperature coefficient.