Constant voltage circuit and oscillation device

1. A constant voltage circuit configured to output a constant voltage for driving an oscillation device including a crystal oscillation circuit, the constant voltage circuit comprising:

a reference voltage circuit configured to output a reference voltage using a mirror current of a constant current source;

a differential amplifier circuit to which the reference voltage and a feedback voltage that is based on the constant voltage are input;

an output transistor configured to output the constant voltage to an output terminal of the constant voltage circuit using an output voltage of the differential amplifier circuit; and

a leakage current detection circuit, between an output terminal of the reference voltage circuit and a gate of the output transistor, and configured to detect a leakage current of a transistor based on the reference voltage,

wherein, when the leakage current detection circuit detects that the leakage current exceeds a predetermined value, the leakage current detection circuit increases a gate-source voltage of the output transistor.

2. The constant voltage circuit according to claim 1 , wherein the leakage current detection circuit comprises:

a PMOS transistor configured to monitor a leakage current;

a first PMOS transistor;

a first NMOS transistor;

a second PMOS transistor;

a second NMOS transistor; and

a third PMOS transistor,

wherein a gate and a source of the PMOS transistor for monitoring a leakage current are grounded and a drain of the PMOS transistor for monitoring a leakage current is connected to a source of the first PMOS transistor,

wherein a gate of the first PMOS transistor is connected to the reference voltage output and a drain of the first PMOS transistor is connected to a drain of the first NMOS transistor,

wherein a gate of the first NMOS transistor is connected to the reference voltage output and a source of the first NMOS transistor is connected to a power supply voltage,

wherein a gate of the second PMOS transistor is connected to the reference voltage output, a source of the second PMOS transistor is grounded, and a drain of the second PMOS transistor is connected to a drain of the second NMOS transistor,

wherein a gate of the second NMOS transistor is connected to the drain of the first PMOS transistor and the drain of the first NMOS transistor, and a source of the second NMOS transistor is connected to the power supply voltage, and

wherein a gate of the third PMOS transistor is connected to the drain of the second PMOS transistor and the drain of the second NMOS transistor, a source of the third PMOS transistor is grounded, and a drain of the third PMOS transistor is connected to the gate of the output transistor.

3. A constant voltage circuit configured to output a constant voltage for driving an oscillation device including a crystal oscillation circuit, the constant voltage circuit comprising:

a reference voltage circuit configured to output a reference voltage using a mirror current of a constant current source;

a differential amplifier circuit to which the reference voltage and a feedback voltage that is based on the constant voltage are input;

an output transistor configured to output the constant voltage to an output terminal of the constant voltage circuit using an output voltage of the differential amplifier circuit; and

a leakage current detection circuit between an output terminal of the constant current source and a gate of the output transistor, and configured to detect a leakage current of a transistor based on a voltage of the output terminal of the constant current source,

wherein, when the leakage current detection circuit detects that the leakage current exceeds a predetermined value, the leakage current detection circuit increases a gate-source voltage of the output transistor.

4. A constant voltage circuit according to claim 3 , wherein the leakage current detection circuit comprises:

an NMOS transistor to monitor a leakage current,

a first NMOS transistor,

a first PMOS transistor,

a second NMOS transistor,

a second PMOS transistor,

a third NMOS transistor,

a third PMOS transistor,

and a fourth PMOS transistor,

wherein a gate and a source of the NMOS transistor for monitoring a leakage current are connected to a power supply voltage and a drain of the NMOS transistor for monitoring a leakage current is connected to a source of the first NMOS transistor, wherein a gate of the first NMOS transistor is connected to a source of the constant current source and a drain of the first NMOS transistor is connected to a drain of the first PMOS transistor,

wherein a gate of the second PMOS transistor is connected to the drain of the first NMOS transistor and the drain of the first PMOS transistor, and a source of the second PMOS transistor is grounded,

wherein a gate of the third NMOS transistor is connected to the drain of the second NMOS transistor and the drain of the second PMOS transistor, a source of the third NMOS transistor is connected to the power supply voltage, and a drain of the third NMOS transistor is connected to a drain of the third PMOS transistor,

wherein a gate of the third PMOS transistor is connected to the drain of the second NMOS transistor and the drain of the second PMOS transistor, and a source of the third PMOS transistor is grounded, and

wherein a gate of the fourth PMOS transistor is connected to the drain of the third NMOS transistor and the drain of the third PMOS transistor, a source of the fourth PMOS transistor is grounded, and a drain of the fourth PMOS transistor is connected to the gate of the output transistor.

5. An oscillation device, comprising:

the constant voltage circuit of claim 1 ; and

an oscillation circuit driven by a voltage of the constant voltage circuit.

6. An oscillation device, comprising:

the constant voltage circuit of claim 3 ; and

an oscillation circuit driven by a voltage of the constant voltage circuit.