Semiconductor integrated circuit and circuit operation method

A method of semiconductor integrated circuit operation, comprising the steps of:

• providing a semiconductor integrated circuit and a power supply circuit preparatively;
• and
• setting up a level of power supply voltage to be fed from the power supply circuit to the semiconductor integrated circuit;
• wherein the semiconductor integrated circuit comprises an internal circuit;
• and a measuring circuit, the internal circuit and the measuring circuit being formed in a semiconductor chip thereof,
• wherein the internal circuit comprises a low-threshold-voltage MOS transistor and a high-threshold-voltage MOS transistor, and the degree of threshold voltage variation of the low-threshold-voltage MOS transistor is larger than the degree of threshold voltage variation of the high-threshold-voltage MOS transistor,
• wherein the measuring circuit detects which one of fast, typical, and slow states is taken by both the low-threshold-voltage MOS transistor and the high-threshold-voltage MOS transistor in the internal circuit,
• wherein a level of the power supply voltage to be fed to the internal circuit is set up in response to result data detected by the measuring circuit,
• wherein, when the result data detected indicates the fast state, the power supply voltage is set to a lower power supply voltage level corresponding to a small variation gradient in terms of the rate of voltage change with respect to speed variation,
• wherein, when the result data detected indicates the typical state, the power supply voltage is set to an intermediate power supply voltage level, and
• wherein, when the result data detected indicates the slow state, the power supply voltage is set to a higher power supply voltage level corresponding to a large variation gradient in terms of the rate of voltage change with respect to speed variation.