Patent ID: 7671683

Claim:
A semiconductor integrated circuit comprising: an amplifier circuit which has an amplifier that includes a phase compensating capacitor, amplifies a difference between input voltages from a first input terminal and a second input terminal, and outputs the amplified difference from an output terminal and a feedback loop formed between the first input terminal and the output terminal; a sine-wave generating section which inputs a sinusoidal voltage to one of the first and second input terminals through a path leading to the one of the first and second input terminals while varying frequency in accordance with a frequency controlling signal; an amplitude measuring section connected to the output terminal which measures an amplitude of a voltage outputted from the output terminal; a controlling section which adjusts a capacitance value of the phase compensating capacitor in accordance with a capacitance controlling signal; and a computing section which outputs the frequency controlling signal, calculates a closed-loop gain at a frequency based on the frequency controlling signal from the amplitude measured by the amplitude measuring section and an amplitude of the sinusoidal voltage outputted from the sine-wave generating section, and outputs the capacitance controlling signal to the controlling section such that a ratio of a value of the closed-loop gain at a first frequency to a value of the closed-loop gain at a second frequency that is lower than the first frequency is a predetermined value.