Power supply voltage detection circuit

#The present invention relates to a power supply voltage detection circuit for outputting a signal upon detecting a power supply voltage, and more particularly to an improvement thereon for preventing the signal from being erroneously output due to a sharp rise of the power supply voltage.

#Referring to FIG. 19 and FIG. 20, a power supply voltage detection circuit 103 designed to detect a power supply voltage based on a predetermined voltage is typically used as a reset signal generation circuit for an arithmetic circuit 102 in a semiconductor integrated circuit 101, for example. Typically, when the power supply voltage is lower than or equal to a predetermined voltage Vo, the power supply voltage detection circuit 103 determines that the power supply voltage is not detected and thus outputs a ‘not detected’ signal to inactivate the arithmetic circuit 102, whereas when the power supply voltage is higher than the predetermined voltage Vo, the power supply voltage detection circuit 103 determines that the power supply is detected and thus outputs a ‘detected’ signal to activate the arithmetic circuit 102. In this way, the semiconductor integrated circuit 101 is operated properly.

#Referring to FIG. 21, the power supply voltage detection circuit 103 includes a voltage division circuit 130 for outputting a signal of an output voltage A, a reference voltage circuit 131 for outputting a signal of a reference voltage B, and a comparison circuit 132 for comparing the output voltage A from the voltage division circuit 130 with the reference voltage B from the reference voltage circuit 131. The voltage division circuit 130 includes two resistors 113 serially connected between the power supply terminal and the ground terminal for linearly dividing the power supply voltage so as to output the output voltage A, which is the voltage at the division point. Since the output voltage A from the voltage division circuit 130 is a voltage obtained through a resistance-based division of the power supply voltage, the output voltage A changes in proportion to the power supply voltage, as illustrated in FIG. 22A. On the other hand, the reference voltage B from the reference voltage circuit 131 is defined to be equal to the output voltage A when the power supply voltage is equal to the predetermined voltage Vo, and the reference voltage B in its steady state is constant irrespective of the power supply voltage. Typically, when the output voltage A is lower than or equal to the reference voltage B, based on the comparison at the comparison circuit 132, it is determined that the power supply voltage is lower than or equal to the predetermined voltage Vo so as to output the ‘not detected’ signal (low signal L in the illustrated example), whereas when the output voltage A is higher than the reference voltage B, it is determined that the power supply voltage is higher than the predetermined voltage Vo so as to output the ‘detected’ signal (high signal H in the illustrated example). Thus, the waveform of the output voltage A and the waveform of the reference voltage B cross each other at a position where the power supply voltage is equal to the predetermined voltage Vo so as to form an intersection at the crossing point, so that the output signal is switched from one to another when crossing the intersection.

#FIG. 1 is a circuit diagram illustrating a general configuration of a power supply voltage detection circuit according to Embodiment 1 of the present invention.

#FIG. 2 is a circuit diagram illustrating a configuration of a semiconductor integrated circuit incorporating the power supply voltage detection circuit.

#FIG. 3 is a circuit diagram illustrating an exemplary configuration of a reference voltage circuit provided in the power supply voltage detection circuit.

#Preferred embodiments of the present invention will now be described with reference to the accompanying drawings.

#Embodiment 1

#FIG. 1 illustrates a general configuration of a power supply voltage detection circuit 3 according to Embodiment 1 of the present invention.