A differential input circuit (FIG. 3A) is disclosed. The circuit includes a first input terminal (drain of 310) and a second input terminal (drain of 312). A first input transistor (310) has a first control terminal and has a current path coupled to the first input terminal. A second input transistor (312) has a second control terminal and has a current path coupled to the second input terminal. A third transistor (306) has a third control terminal and has a current path between a first differential input terminal (Vin+) and the first control terminal. A fourth transistor (308) has a fourth control terminal and has a current path between a second differential input terminal (Vin−) and the second control terminal.

An amplifier that amplifies a differential signal includes first and second input terminals for receiving two input signals; first and second diodes each including an anode and a cathode, the anodes being electrically connected to the first and second input terminals; first and second bias current sources being respectively electrically connected to the cathodes of the first and second diodes; an operational amplifier connected to the cathode of the first diode and the cathode of the second diode and configured to amplify a differential signal between signals generated at the cathodes of the first and second diodes; a capacitive element being electrically connected between an input and an output of the operational amplifier; and a differential amplifier provided between the operational amplifier and the first and second input terminals and configured to amplify the two input signals. The first and second bias current sources include a current mirror circuit.

An amplifier that amplifies a differential signal includes first and second input terminals for receiving two input signals; first and second diodes each including anode and cathode, the anodes being electrically connected to the first and second input terminals; first and second bias current sources being respectively electrically connected to the cathodes of the first and second diodes; an operational amplifier connected to the cathode of the first diode and the cathode of the second diode and configured to amplify a differential signal between signals generated at the cathodes of the first and second diodes; a capacitive element being electrically connected between an input and an output of the operational amplifier; and a differential amplifier provided between the operational amplifier and the first and second input terminals and configured to amplify the two input signals. The first and second bias current sources include a current mirror circuit.

An instrumentation absolute value differential amplifier is used as part of an electroencephalogram, electromyogram or electrocardiogram to quantify the excitation state of a user, processing and transmitting this information as a control signal for a user feedback device. In one possible arrangement, this feedback device includes a wireless sex toy which responds to the sent control information, acting as a mind controlled sex toy. This provides a simple, intuitive, aesthetically appealing interface for creating a unique sexual experience. The use of an instrumentation absolute value differential amplifier is sufficient to monitor the desired signals while reducing the number of parts required and allowing for less precise tolerances than traditional biological monitoring circuits, thus decreasing the cost of production.

Provided is a compensation circuit capable of improving compensation precision for manufacturing variations. The compensation circuit includes a manufacturing variation detection circuit which detects manufacturing variation of a transistor based on a first voltage output from an output terminal of the transistor having an input terminal applied with a substantially constant first current to temperature or based on a second current output from an output terminal of the transistor having an input terminal applied with a substantially constant second voltage to temperature, and a voltage generation circuit which generates a supply voltage supplied to an electric circuit based on the manufacturing variation. The first current corresponds to the substantially constant second voltage to temperature, and the first voltage corresponds to the substantially constant second current to temperature.

Disclosed is a class-D amplifier including a first output circuit, a first capacitor, a pulse width modulator, and a slew rate limiting amplifier. The first output circuit includes first and second switching devices that are connected in series between first and second power supply lines. The first capacitor is connected between the first and second power supply lines. The pulse width modulator generates a pulse width modulated switching signal based on a triangular wave and an audio signal, and provides the switching signal to the first output circuit. The slew rate limiting amplifier is connected to an input part of the pulse width modulator to which the audio signal is provided, and limits a slew rate of output. The sound-producing device is connected in series to an inductor connected to a first output node of the first output circuit. The sound-producing device and the inductor constitute an LC filter.