Apparatus and method for determining a temperature of a temperature sensing element

A method of measuring a temperature of a temperature sensing element having a temperature dependent resistance, the method comprising:

• charging a capacitor to a supply voltage;
• determining a reference discharge time to discharge the capacitor through a reference resistor in parallel with the capacitor from the supply voltage to a reference voltage;
• charging the capacitor to the supply voltage again;
• determining a temperature evaluation discharge time to discharge the capacitor from the supply voltage to the reference voltage through the reference resistor and the temperature sensing element in parallel with the reference resistor, the capacitor also connected in parallel with the reference resistor and the temperature sensing element between a common node and ground when the temperature evaluation discharge time is measured;
• calculating a discharge ratio value in accordance discharge time ratio equal to the temperature evaluation discharge time divided by the reference discharge time;
• and
• comparing the discharge ratio value to a plurality of values uniquely associated with temperatures to determine a measured temperature.

A microprocessor for measuring temperature, the microprocessor comprising:

• a first general purpose input-output (GPIO) port to connect to a reference resistance, a capacitor, and a first port of a temperature sensing element having a resistance dependent on temperature;
• a second GPIO port to connect to a second port of the temperature sensing element;
• a voltage comparator to determine when a voltage across the capacitor is equal to a reference voltage;
• and
• a controller configured to:
• set the second GPIO port to an off state to present a high impedance greater than the reference resistance, set the first GPIO port to a logic high voltage to charge the capacitor to the logic high voltage before setting the first GPIO port to the off state;
• determine a reference discharge time for discharging the capacitor from the logic high voltage to the reference voltage through the reference resistance while the first GPIO port and the second GPIO port are in the off state;
• set the second GPIO port to a logic low voltage to ground the second port of the temperature sensing element, set the first GPIO port to the logic high voltage before setting the first GPIO port to the off state circuit state;
• determine a temperature evaluation discharge time for discharging the capacitor from the logic high voltage to the reference voltage through a parallel combination resistance of the reference resistance connected in parallel with the temperature sensing element, the capacitor also connected in parallel with the reference resistance and the temperature sensing element between a common node and ground when the temperature evaluation discharge time is measured;
• and
• determine a temperature of the temperature sensing element based on a discharge time ratio of the reference discharge time and the temperature evaluation discharge time.