Common signal conditioning circuit for temperature sensor
A ratiometric temperature measurement system includes a sensing circuit to measure a temperature and a controller to determine a resistance corresponding to the sensing circuit. The sensing circuit includes a temperature sensing circuit and a current sensor. The sensing circuit utilize an electrical current to output a first voltage indicative of a first voltage differential across the temperature sensing circuit and to output a second voltage indicative of a second voltage differential across the current sensor. The controller is configured to determine a resistance corresponding to the temperature sensing circuit based at least in part on the first and second voltage differentials. The controller determines a temperature value indicative of the measured temperature based on the resistance.
1. A ratiometric temperature measurement system comprising:
a sensing circuit configured to measure a temperature, the sensing circuit including a temperature sensing circuit and a current sensor, the sensing circuit being configured to utilize an electrical current (Io) to output a first voltage indicative of a first voltage differential (V T_SENSOR ) across the temperature sensing circuit and to output a second voltage indicative of a second voltage differential (V C_SENSOR ) across the current sensor; and
a controller configured to determine a resistance (R T_SENSOR ) corresponding to the temperature sensing circuit based at least in part on the first and second voltage differentials (V T_SENSOR and V C_SENSOR ), and to determine a temperature value (T OUT ) indicative of the measured temperature based on the resistance (R T_SENSOR ), wherein the controller comprises:
memory configured to store a look-up table (LUT) populated with a plurality of predetermined resistance values that are mapped to corresponding predetermined temperature values; and
a processor in signal communication with the memory, the processor configured to compare the resistance (R T_SENSOR ) to the predetermined resistance values, select a predetermined temperature value corresponding to the predetermined resistance value that matches the resistance (R T_SENSOR ), and output the selected predetermined temperature value as the temperature value (T OUT ).
2. The ratiometric temperature measurement system of claim 1 , wherein the controller determines a current level (I exc ) of the current (I o ) based on the second voltage differential (V C_SENSOR ) indicated by the current sensor and a resistance (R C_SENSE ) of the current sensor.
3. The ratiometric temperature measurement system of claim 2 , wherein the resistance (R T_SENSOR ) is determined as a ratio of the first voltage differential (V T_SENSOR ) to the current level (I exc ).
4. The ratiometric temperature measurement system of claim 3 , wherein the sensing circuit comprises:
a temperature sensor configured to effect the first voltage differential (V T_SENSOR ) in response to the current (Io); and
an adjustable linearization resistance element (R p ) configured to selectively add or remove a resistance realized by the temperature sensor.
5. The ratiometric temperature measurement system of claim 4 , wherein the temperature sensor includes a first terminal connected to the current sensor to receive the current and a second terminal connected to a ground potential.
6. The ratiometric temperature measurement system of claim 5 , wherein the temperature sensor is an RTD, and the adjustable linearization resistance element is connected in parallel with the RTD so as to establish an open circuit in parallel with the RTD.
7. The ratiometric temperature measurement system of claim 5 , wherein the temperature sensor is an NTC and the adjustable linearization resistance element is connected in parallel with the NTC to establish a targeted resistance that shunts the NTC and linearizes the first voltage differential.
8. The ratiometric temperature measurement system of claim 5 , further comprising a current excitation circuit including a constant current source configured to generate the current.
9. The ratiometric temperature measurement system of claim 8 , wherein the current sensor is in signal communication with the current excitation circuit and is configured to effect the second voltage differential (V C_SENSOR ) thereacross in response to the current.
10. The ratiometric temperature measurement system of claim 9 , wherein the current sensor includes a current sense resistor having a fixed resistance that defines the resistance (R C_SENSE ) of the current sensor.
11. The ratiometric temperature measurement system of claim 10 , wherein a voltage drop across the sense resistor defines the second voltage differential (V C_SENSOR ).
12. The ratiometric temperature measurement system of claim 11 , further comprising:
a multiplexer (MUX) configured to selectively output the first voltage differential (V T_SENSOR ) or the second voltage differential (V C_SENSOR ) in response to a control signal generated by the controller; and
an amplifier circuit in signal communication with the MUX, the amplifier circuit configured to amplify the first voltage differential (V T_SENSOR ) and to amplify the second voltage differential (V C_SENSOR ).
13. The ratiometric temperature measurement system of claim 12 , further comprising a filter circuit in signal communication with the sensing circuit, the filter circuit configured to filter the first voltage differential (V T_SENSOR ) and the second voltage differential (V C_SENSOR ) and output the filtered first and second voltage differentials to the amplifier circuit.
14. The ratiometric temperature measurement system of claim 13 , further comprising an analog-to-digital converter (ADC) including an input connected to the amplifier circuit and an output connected to the controller, the ADC being configured to generate a first digital signal indicative of the first voltage differential (V T_SENSOR ) and a second digital signal indicative of the second voltage differential (V C_SENSOR ).
15. A method of measuring a temperature, the method comprising:
delivering an electrical current (Io) to a sensing circuit;
outputting a first voltage from a temperature sensor included in a temperature sensing circuit included in the sensing circuit in response to the electrical current, the first voltage indicative of a first voltage differential (V T_SENSOR );
selectively adding or removing a resistance realized by the temperature sensor using an adjustable linearization resistance element (R p ):
outputting a second voltage from a current sensor included in the sensing circuit, the second voltage indicative of a second voltage differential (V C_SENSOR );
determining, using a controller, a resistance (R T_SENSOR ) corresponding to the temperature sensing circuit based at least in part on the first and second voltage differentials (V T_SENSOR and V C_SENSOR ); and
determining, using the controller, a temperature value (T OUT ) indicative of the temperature based on the resistance (R T_SENSOR ).
16. The method of claim 15 , further comprising:
populating a look-up table (LUT) with a plurality of predetermined resistance values that are mapped to corresponding predetermined temperature values;
comparing, by the controller, the resistance (R T_SENSOR ) to the predetermined resistance values;
selecting, by the controller, a predetermined temperature value corresponding to the predetermined resistance value that matches the resistance (R T_SENSOR ); and
outputting, by the controller, the selected predetermined temperature value as the temperature value (T OUT ).
17. The method of claim 15 , further comprising determining, using the controller, a current level (I exc ) of the current (I o ) based on the second voltage differential (V C_SENSOR ) indicated by the current sensor and a resistance (R C_SENSE ) of the current sensor.
18. The method of claim 17 , further comprising determining the resistance (R T_SENSOR ) as a ratio of the first voltage differential (V T_SENSOR ) to the current level (I exc ).