Patent ID: 7427158

Claim:
A thermal sensing system comprising: a reference voltage generator configured to generate a non-constant first reference voltage that varies as a known first function of temperature; a thermal sensor configured to generate a sensor voltage that varies as a known second function of temperature, wherein the second function intersects the first function; and a first comparator configured to receive the sensor voltage and the first reference voltage, compare the sensor voltage and the first reference voltage, and generate a first comparison output signal based on the comparison of the sensor voltage and the first reference voltage; wherein the thermal sensor and the reference voltage generator are integrated into a single circuit that includes an operational amplifier, first, second and third transistors, first and second PN junctions, wherein the second PN junction has a cross-sectional area greater than a cross-sectional area of the first PN junction, and first and second resistors, wherein the source of each of the transistors is tied together and connected to a voltage source, wherein the gate of each of the transistors is tied together and connected to an output of the operational amplifier, wherein the drain of the first transistor is coupled to an inverting input of the operational amplifier and the drain of the second transistor is coupled to a non-inverting input of the operational amplifier, wherein the first PN junction is coupled between the drain of the first transistor and ground, wherein the first resistor and the first PN junction are coupled in series between the drain of the second transistor and ground, wherein the second resistor is coupled between the drain of the third transistor and ground, and wherein the first reference voltage comprises a voltage at the drain of the third transistor.