Patent ID: 7417489

Claim:
A semiconductor integrated circuit comprising: a power controller which outputs a voltage select signal for selecting one of at least two types of voltages, and a clock select signal for selecting one of at least two types of clock frequencies as a clock; a clock generator which receives the clock select signal, and generates and outputs the clock; a power supply voltage controller which receives the voltage select signal, and generates and outputs a power supply voltage at an arbitrary voltage change rate; and a circuit portion which receives the clock and power supply voltage and performs processing, wherein when the power supply voltage is to be switched to a second voltage lower than a first voltage while said circuit portion is performing processing by using a clock having a first frequency and a power supply voltage having the first voltage, said clock generator outputs a clock having a second frequency lower than the first frequency, and, after that, said power supply voltage controller outputs a power supply voltage which is changed from the first voltage to the second voltage at the arbitrary voltage change rate, on the basis of signals from said power controller; wherein said power supply voltage controller comprises: a maximum voltage change rate limiting unit comprising a first current source and first switch connected in series between a power supply terminal and reference voltage output terminal, a second switch connected in series between a first input terminal which receives the first voltage and said reference voltage output terminal, a third switch connected in series between a second input terminal which receives one type of a voltage as the second voltage and said reference voltage output terminal, a fourth switch and second current source connected in series between said reference voltage output terminal and a ground terminal, a capacitor connected between said reference voltage output terminal and ground terminal, a first voltage comparator which compares the first voltage from said first input terminal with a reference voltage from said reference voltage output terminal, and outputs a first comparison result, a second voltage comparator which compares the second voltage from said second input terminal with the reference voltage from said reference voltage output terminal, and outputs a second comparison result, a switching controller which receives the voltage select signal and first and second comparison results, and controls ON/OFF operations of said first to fourth switches; and a voltage output unit which is connected to said power supply terminal, receives the reference voltage output from said reference voltage output terminal, and outputs, to said circuit portion, a voltage having the reference voltage as the power supply voltage.