Abstract: An amplifier circuit 1001 with a variable temperature coefficient of a gain is an amplifier circuit with a variable temperature coefficient of a gain in which a variable resistor VR is connected between a first signal and a second signal having temperature coefficients of an amplification factor different from each other, a variable output of the variable resistor VR is connected to an input of a buffer amplifier Ub, and an output of the buffer amplifier Ub is used as an output Vo, wherein the first signal is an output of a first temperature coefficient circuit 100, and the second signal is an output of another amplifier circuit 501.

Abstract: A capacitance measuring circuit measures an electrostatic capacitance formed between a first conductor that receive an AC signal and a second conductor. The capacitance measuring circuit includes an amplifier including an input and an output; signal detection means including a negative feedback unit that has a feedback capacitance and applies a negative feedback from an output of the amplifier to an input of the amplifier, wherein an input of the amplifier is connected to the second conductor and is virtually grounded by the negative feedback unit and an AC signal of an amplitude in a functional relation with the electrostatic capacitance is output; and measuring means that is connected to an output of the signal detection means and has a function of measuring at least an amplitude of an AC signal output of the signal detection means.

Abstract: A capacitance measuring circuit measures an electrostatic capacitance formed between a first conductor that receive an AC signal and a second conductor. The capacitance measuring circuit includes an amplifier including an input and an output; signal detection means including a negative feedback unit that has a feedback capacitance and applies a negative feedback from an output of the amplifier to an input of the amplifier, wherein an input of the amplifier is connected to the second conductor and is virtually grounded by the negative feedback unit and an AC signal of an amplitude in a functional relation with the electrostatic capacitance is output; and measuring means that is connected to an output of the signal detection means and has a function of measuring at least an amplitude of an AC signal output of the signal detection means.

Abstract: An amplifier circuit whose frequency response has almost no soft knee characteristic or no peak when inverting input capacitance Csin varies and when feedback capacitance Cf is a fixed value of small capacitance, and a feedback circuit is provided. The amplifier circuit includes a plurality of amplifiers each of which negative feedback is provided to and which are connected in series, and a feedback means (feedback circuit) which is connected to an output side of an amplifier near output of the amplifier circuit and an input side of an amplifier near input of the amplifier circuit. These amplifiers are ones in the plurality of amplifiers. One or odd numbers of amplifiers in the plurality of amplifiers are inverting amplifiers.

Abstract: An amplifier circuit whose frequency response has almost no soft knee characteristic or no peak when inverting input capacitance Csin varies and when feedback capacitance Cf is a fixed value of small capacitance, and a feedback circuit is provided. The amplifier circuit includes a plurality of amplifiers each of which negative feedback is provided to and which are connected in series, and a feedback means (feedback circuit) which is connected to an output side of an amplifier near output of the amplifier circuit and an input side of an amplifier near input of the amplifier circuit. These amplifiers are ones in the plurality of amplifiers. One or odd numbers of amplifiers in the plurality of amplifiers are inverting amplifiers.

Abstract: An amplifier circuit whose frequency response has almost no soft knee characteristic or no peak when inverting input capacitance Csin varies and when feedback capacitance Cf is a fixed value of small capacitance, and a feedback circuit is provided. The amplifier circuit includes a plurality of amplifiers each of which negative feedback is provided to and which are connected in series, and a feedback means (feedback circuit) which is connected to an output side of an amplifier near output of the amplifier circuit and an input side of an amplifier near input of the amplifier circuit. These amplifiers are ones in the plurality of amplifiers. One or odd numbers of amplifiers in the plurality of amplifiers are inverting amplifiers.

Abstract: An amplifier circuit whose frequency response has almost no soft knee characteristic or no peak when inverting input capacitance Csin varies and when feedback capacitance Cf is a fixed value of small capacitance, and a feedback circuit is provided. The amplifier circuit includes a plurality of amplifiers each of which negative feedback is provided to and which are connected in series, and a feedback means (feedback circuit) which is connected to an output side of an amplifier near output of the amplifier circuit and an input side of an amplifier near input of the amplifier circuit. These amplifiers are ones in the plurality of amplifiers. One or odd numbers of amplifiers in the plurality of amplifiers are inverting amplifiers.