Oscillator, and clock generator, semiconductor device, and electronic device including the same

1. An oscillator comprising:

a reference voltage generator;

an oscillation element configured to oscillate by either a drive voltage or drive current and output an oscillation signal;

a peak hold element configured to detect a peak level of the oscillation signal for output; and

a regulator configured to increase or decrease the drive voltage or drive current in accordance with the reference voltage generated by the reference voltage generator and the peak level output from the peak hold element, wherein

the reference voltage generator comprises a fourth PMOS transistor and a third NMOS transistor to output a voltage of a sum of a threshold of the fourth PMOS transistor and a threshold of the third NMOS transistor as the reference voltage.

2. An oscillator according to claim 1 , wherein:

the reference voltage generator comprises a third constant current source, the fourth PMOS transistor, and the third NMOS transistor connected in series;

a source of the third NMOS transistor is grounded, a drain and a gate of the third NMOS transistor are connected with each other, the drain of the third NMOS transistor is connected with a gate and a drain of the fourth PMOS transistor; and

a source of the fourth PMOS transistor is supplied with current from the third constant current source to output, as the reference voltage, a voltage of the sum of the threshold of the fourth PMOS transistor and the threshold of the third NMOS transistor.

3. A clock generator comprising the oscillator according to claim 1 .

4. A semiconductor device comprising the clock generator according to claim 3 .

5. An electronic device comprising the semiconductor device according to claim 4 .