Triangular wave generating circuit, and charging and discharging control circuit

1. A triangular wave oscillation circuit, comprising:

a first current source circuit for generating a current;

a capacitor;

a reference voltage circuit for generating a plurality of reference voltages;

a comparator circuit for comparing a voltage of the capacitor with the plurality of reference voltages to output a switching signal for switching between charging and discharging of the capacitor based on a result obtained by the comparison;

a charging and discharging circuit for performing one of the charging and discharging of the capacitor with the current specified by the first current source circuit in response to the switching signal from the comparator circuit; and

a switch circuit for switching between the plurality of reference voltages in response to the switching signal from the comparator circuit,

wherein the charging and discharging circuit includes:

an inverter circuit for inverting the switching signal from the comparator circuit;

a discharging reference potential generating circuit for generating a discharging reference potential which is a reference potential for discharging the capacitor;

a first NMOS transistor having a drain connected with a connection point between the first current source circuit and the capacitor, and a gate connected with the discharging reference potential generated by the discharging reference potential generating circuit;

a second NMOS transistor having a gate to which the switching signal is inputted through the inverter circuit, a drain connected with the gate of the first NMOS transistor, and a source connected with a source of the first NMOS transistor; and

a third NMOS transistor having a gate to which the switching signal is inputted, a drain connected with a connection point between the source of the first NMOS transistor and the source of the second NMOS transistor, and a source grounded.

2. An triangular wave oscillation circuit according to claim 1 , wherein when the capacitor is charged:

the charging and discharging circuit operates such that the second NMOS transistor is turned on and the third NMOS transistor is turned off to make potentials of the source and the gate of the first NMOS transistor equal to the discharging reference potential; and

the drain and the source of the first NMOS transistor are electrically disconnected with each other by operation of the charging and discharging circuit to charge the capacitor with the current from the first current source circuit.

3. An triangular wave oscillation circuit according to claim 1 , wherein when the capacitor is discharged:

the charging and discharging circuit operates such that the second NMOS transistor is turned off and the third NMOS transistor is turned on to make the potential of the source of the first NMOS transistor lower than the discharging reference potential which is the potential of the gate of the first NMOS transistor; and

the drain and the source of the first NMOS transistor are electrically connected with each other by operation of the charging and discharging circuit to discharge the capacitor.

4. An triangular wave oscillation circuit according to claim 1 , wherein:

the discharging reference potential generating circuit includes:

a second current source circuit for generating a current;

a fourth NMOS transistor having a drain connected with the second current source circuit; and

a fifth NMOS transistor having a drain connected with a source of the fourth NMOS transistor, a source grounded, and a gate applied with a power supply voltage;

the gate of the first NMOS transistor is connected with a gate of the fourth NMOS transistor; and

a connection point between the second current source circuit and the drain of the fourth NMOS transistor is connected with a connection point between the gate of the fourth NMOS transistor and the gate of the first NMOS transistor.