US Patent 10458857 Accurate on-chip temperature sensing using thermal oscillator

A calibrated temperature sensor includes a power on oscillator responsive to a calibration enable signal for providing a power on clock signal, a temperature dependent oscillator responsive to said calibration enable signal for providing a temperature dependent clock signal, and a measurement logic circuit. The measurement logic circuit counts a first number of pulses of the temperature dependent clock signal during a first calibration period using the power on clock signal, a second number of pulses of the temperature dependent clock signal during a second calibration period using a system clock signal, and a third number of pulses of the power on clock signal over a third calibration period using the system clock signal, and a fourth number of pulses of the temperature dependent clock signal using the system clock signal during a normal operation mode, wherein the first calibration period precedes both the second and third calibration periods.