Patent ID: 7274218

Claim:
An integrated circuit comprising: a first input terminal that applies an input signal with a high level and a low level, the input signal having a DC component; a second input terminal that applies a reference signal with a constant level; a first amplifier circuit that generates a first control signal and includes a first input terminal connected to the first input terminal that applies the input signal and a second input terminal connected to the second input terminal that applies the reference signal; a second amplifier circuit that generates a second control signal and includes a first input terminal connected to the first input terminal that applies the input signal and a second input terminal connected to the second input terminal that applies the reference signal; and a third amplifier circuit including a first controllable resistor that is controlled by the first control signal and a second controllable resistor that is controlled by the second control signal; wherein: the first and second amplifier circuits are configured such that, upon driving with the high level of the input signal, the first amplifier circuit generates the first control signal at one level, so that the first controllable resistor of the third amplifier circuit is controlled at a low-resistance level, and the second amplifier circuit generates the second control signal at one level, so that the second controllable resistor of the third amplifier circuit is controlled at a high-resistance level, when the constant level of the reference signal is between the high and low levels of the input signal; the first and second amplifier circuits are further configured such that, upon driving with the low level of the input signal, the first amplifier circuit generates the first control signal at another level, so that the first controllable resistor of the third amplifier circuit is controlled at a high-resistance level, and the second amplifier circuit generates the second control signal at another level, so that the second controllable resistor of the third amplifier circuit is controlled at a low-resistance level, when the constant level of the reference signal is between the high and low levels of the input signal; the first amplifier circuit comprises a controllable resistor including a control terminal that sets a resistance value, the control terminal of the controllable resistor of the first amplifier circuit is connected to the second input terminal that applies the reference signal; the controllable resistor of the first amplifier circuit is configured to have a first resistance value when the reference signal has a level of the DC component of the input signal; and the controllable resistor of the first amplifier circuit is further configured to have a second resistance value when the reference signal exceeds the level of the DC component of the input signal, with the second resistance value lying below the first resistance value.