Power-on clear circuit
View Patent ↗A power-ON-clear circuit has a reset period when the power supply stops temporarily (or instantaneously) and then that power supply is restored. The power-ON-clear circuit 30 of a semiconductor integrated circuit 200 comprises: a capacitor C 31 of which one end is connected to the external power-supply voltage Vcc 1 ; an N-channel MOS transistor Q 31 of which the drain is connected to the other end of the capacitor C 31 , the source is connected to the ground potential, and the gate is connected to the external power-supply voltage by way of a resistor R 31 ; and an inverter INV 31 that is connected to the connecting point between the capacitor C 31 and MOS transistor Q 31 in a stage connection, and is connected to the power supply between the internal power-supply voltage Vcc 2 and the ground potential.
1. A semiconductor integrated circuit comprising:
a voltage regulator that outputs an external power-supply voltage and an internal power-supply voltage lower than the external power-supply voltage; and
a power-ON-clear circuit comprising,
an inverter with a power-supply terminal connected to the internal power-supply voltage and an input terminal receiving the external power-supply voltage, said inverter outputting a reset signal each time immediately after said external power-supply voltage is interrupted and restored, and
a MOS transistor and a capacitor that are connected in series between said external power-supply voltage and a ground potential, a connecting point between said MOS transistor and said capacitor being connected to said input terminal of said inverter,
said MOS transistor having terminals connected to said external power-supply voltage and the ground potential and is turned ON when said external power-supply voltage is supplied, and
said capacitor having a terminal connected to one of the external power-supply voltage and the ground potential and is charged by said external power-supply voltage when said external power-supply voltage is supplied.
2. The semiconductor integrated circuit of claim 1 , wherein
said MOS transistor comprises an N-channel transistor, and
said capacitor and said MOS transistor that is ON form a differentiating circuit.
3. The semiconductor integrated circuit of claim 1 , wherein
said MOS transistor comprises a P-channel transistor, and
said capacitor and MOS transistor that is ON form an integrating circuit.
4. The integrated circuit as claimed in claim 1 , wherein said reset signal has a power source voltage level during a reset period.
5. The integrated circuit as claimed in claim 4 , wherein said power source voltage is a ground voltage.
6. The integrated circuit as claimed in claim 1 , wherein said reset signal has said internal power supply voltage during a reset period.