Production-test die temperature measurement method and apparatus

A method to measure temperature in a temperature sensing circuit, the method comprising:

• 1) coupling together the temperature sensing circuit including at least one bipolar transistor and a current mirror with a gain, and a programmable current-mirror output coupled to a collector of the bipolar transistor;
• 2) setting the gain of the current mirror to a first value from a set of current gain values;
• 3) measuring an output signal produced by the temperature sensing circuit by
• a) setting a voltage magnitude of an input voltage between a first I/O pad and a third I/O pad of the temperature sensing circuit,
• b) changing a switchable-resistance between at least a first resistance value and a second resistance value, the switchable-resistance disposed between the first I/O pad of the temperature sensing circuit and a base of the bipolar transistor,
• c) measuring, between the first I/O pad and a second I/O pad of the temperature sensing circuit, the output signal in response to the input voltage, and
• increasing the voltage magnitude of the input voltage, and repeating steps a through c, in response to the output signal being measured with the second resistance applied being greater than the output signal being measured with the first resistance applied, decreasing the voltage magnitude of the input voltage, and repeating steps a through c, in response to the output signal being measured with the second resistance applied being less than the output signal being measured with the first resistance applied;
• repeating steps 2 through 3 until at least each of the current gain values has been used to set the gain of the current mirror and the output signal measured;
• and
• 4) calculating a temperature produced by the temperature sensing circuit by using each output signal that has been measured for each of the set of current gain values used to set the gain of the current mirror.