Patent ID: 8008967

Claim:
A power supply voltage adjusting device which adjusts a power supply voltage of a semiconductor integrated circuit configured by plural types of transistors having different threshold voltages, comprising: a first ring oscillator to oscillate a first oscillation signal, all of transistors included in the first ring oscillator, which are provided in a ring path of the first ring oscillator and are used for oscillating the first oscillation signal, having a high threshold value; a second ring oscillator to oscillate a second oscillation signal, all of transistors included in the second ring oscillator, which are provided in a ring path of the second ring oscillator and are used for oscillating the second oscillation signal, having a low threshold value; a first counter to count first oscillation frequency of the first oscillation signal to output a first count value and to count second oscillation frequency of the second oscillation signal to output a second count value; a converter to convert the first count value into a first power supply voltage corresponding to the high threshold value and the second count value into a second power supply voltage corresponding to the low threshold value; and a controller to output a control signal indicating one of the first power supply voltage and the second power supply voltage.