SIGNAL INPUT CIRCUIT

PURPOSE:To realize a signal input circuit without temperature characteristic, which makes a hysteresis width constant irrespective of temperature variation by designing a circuit element so as to let a differential value due to the temperature of the hysteresis width be zero. CONSTITUTION:As plural series connection circuit elements generating reference voltage at a prescribed connecting node B by receiving the supply of bias current I3, seventh and eighth resistances 22 and 24 provided with positive temperature characteristic as the level of reference voltage and diodes 23 and 25 provided with negative temperature characteristic for the level of reference voltage are used. Furthermore, a transistor 21 is connected to the second diode 25 and the eighth resistance 24 in parallel so as to form the bias route of bias current I3 in accordance with the level of an input signal. Consequently, the hysteresis width is provided with a characteristic of which variation with respect to temperature variation is larger between the positive temperature characteristic by the resistances and the negative temperature characteristic by the diodes.