A temperature sensing apparatus disposed inside a chip includes first and second current generation circuits, first and second current-to-frequency converters, and a counting unit. The first current generation circuit is configured to generate a first current varying proportional to the temperature of the temperature sensing apparatus. The second current generation circuit is configured to generate a second current independent of temperature. The first current-to-frequency converter is configured to generate a first frequency signal with a first frequency indicative of the first current, and the second current-to-frequency converter is configured to generate a second frequency signal with a second frequency indicative of the second current. The counting unit is configured to generate a digital signal indicative of the temperature according to the difference between the first and second frequencies.