Temperature estimation circuit and count value correction circuit

A count value correction circuit comprising:

• a first oscillator to generate a first oscillating signal having a smaller temperature-related change rate of an oscillating frequency than a first predetermined value and having a small temperature-related change;
• a second oscillator to generate a second oscillating signal having an oscillating frequency linearly changing with respect to a temperature;
• an enable period setting unit to set a count period for a predetermined number of oscillations of the first oscillating signal as an enable period;
• a first counter to count the number of oscillations of the second oscillating signal during the enable period;
• a first memory to store therein a count output value outputted from the first counter when a test at a first temperature is performed, as a first count value;
• a second memory to store therein a count output value outputted from the first counter when a test at a second temperature is performed, as a second count value;
• an operation unit to executes a computation to calculate an operation temperature based on an operation-time count value outputted from the first counter during a normal operation, the first count value, and the second count value;
• a second counter to count the number of oscillations of the first oscillating signal;
• a first selector to select either one of the second oscillating signal and a third oscillating signal
• having a smaller temperature-related change rate of the oscillating frequency than a second predetermined value and having a small temperature-related change, and output the selected signal to the first counter;
• a third memory to store therein the count output value outputted from the first counter during the enable period as a third count value when the test at the first temperature is performed and the first selector selects the third oscillating signal;
• a fourth memory to store therein the count output value outputted from the first counter during the enable period as a fourth count value when the test at the second temperature is performed and the first selector selects the third oscillating signal;
• an oscillation characteristic estimation unit to estimate a reference oscillating frequency of the first oscillator at a reference temperature and a temperature coefficient of the reference oscillating frequency, based on the third count value and the fourth count value;
• a correction value table in which a correction value is described for each of the temperatures, the correction value being a value used to correct a shift of a count value of the second counter when the first oscillating signal fluctuates from the reference oscillating frequency;
• and
• a correction unit to correct the count value of the second counter by reading out a correction value corresponding to a combination of the reference oscillating frequency and the temperature coefficient, and the operation temperature outputted from the operation unit, from the correction value table.