PURPOSE: To decrease the number of elements and to reduce the size by detecting the voltage of a capacitor, charged according to the level of an input signal, through a Schmitt circuit composed of MOS transistors (TR), and thus discharging the capacitor.
CONSTITUTION: When an input signal VIN is applied to an input terminal IN, a gate voltage which corresponds to the signal VIN is applied to gates of MOSTRs M5 and M6, so a capacitor C is integrated by a current which corresponds to the signal VIN. A Schmitt circuit 23 consists of MOSTRs M11∼M15. When the potential of the capacitor C is low, the M11 is turned off and an output OUT has a high level. When the potential of the capacitor C is higher than the output VB of a voltage switching circuit 232, the M11 turns on. Then, the output OUT has a high level and the capacitor C is discharged through the M8 and M6 to hold the source voltage of the M11 at the earth potential because the M13 turns on, thereby turning on the M11 securely.
MATSUMURA TOSHIHIKO
ITOU AKIHIKO
