Oscillation circuit

An oscillation circuit comprising:

• a reference voltage generation circuit that adds a proportional-to-absolute-temperature (PTAT) output, which increases in proportion to an absolute temperature, to a complementary-to-absolute-temperature (CTAT) output, which decreases in proportion to an absolute temperature, to generate and output a reference voltage;
• a first switching unit coupled to the reference voltage generation circuit, wherein the first switching unit switches an adding ratio of the PTAT output and the CTAT output to minimize a variation in an output from the reference voltage generation circuit that depends on temperature;
• a current source that generates current which has a current value based on the output from the reference voltage generation circuit;
• a regulator circuit that generates constant voltage based on the output from the reference voltage generation circuit;
• a first capacitor and a second capacitor, each including one terminal coupled to the current source and charged and discharged by the current of the current source;
• an inverter coupled to another terminal of the second capacitor, wherein the inverter drives the second capacitor using the constant voltage supplied from the regulator circuit as a power supply;
• a second switching unit that switches a value of the current of the current source to adjust an oscillation frequency;
• and
• a third switching unit coupled to the first capacitor, wherein the third switch unit switches capacitance of the first capacitor to adjust oscillation amplitudes at the one terminal of each of the first and second capacitors;
• wherein trimming of the first switching unit, the second switching unit, and the third switching unit is performed to generate an oscillation signal having a desired frequency.