Image Number 2 for United States Patent #6166588.
A power supply circuit comprising a reference voltage generating circuit and an internal voltage generating circuit, whereby a stable internal voltage can be supplied. The reference voltage generating circuit comprises a resistor, of which one end is coupled to a power supply terminal, and a first NMOSFET, of which the drain electrode is coupled to the other end of the resistor, the source electrode is coupled to an earth terminal, and the gate electrode is coupled to the drain electrode. The internal voltage generating circuit comprises a second NMOSFET, of which the gate electrode is coupled to the drain electrode of the first NMOSFET and the source electrode is coupled to the earth terminal, and a constant voltage generating circuit, coupled between the drain electrode of the second NMOSFET and the power supply terminal, which outputs a constant voltage. The gate length of the first NMOSFET is formed longer than the gate length of the second NMOSFET.