Each sub-stage of an amplifier stage includes a resistor coupled to another resistor in an adjacent sub-stage or to a high DC voltage, the resistor and the other resistor forming part of a string of equal valued resistors; an FET having a source coupled to a cathode of a Zener diode coupled in parallel with a capacitor, a drain coupled to another sub-stage in the string, an output node of the amplifier stage, or the high DC voltage; and at least one active device coupled to a gate of the FET and coupled to the resistor for providing high impedance between a voltage on a node of the resistor and the gate of the FET and a low impedance between the at least one active device and the gate of the FET, the at least one active device coupled to both the cathode and an anode of the Zener diode.

Each sub-stage of an amplifier stage includes a resistor coupled to another resistor in an adjacent sub-stage or to a high DC voltage, the resistor and the other resistor forming part of a string of equal valued resistors; an FET having a source coupled to a cathode of a Zener diode coupled in parallel with a capacitor, a drain coupled to another sub-stage in the string, an output node of the amplifier stage, or the high DC voltage; and at least one active device coupled to a gate of the FET and coupled to the resistor for providing high impedance between a voltage on a node of the resistor and the gate of the FET and a low impedance between the at least one active device and the gate of the FET, the at least one active device coupled to both the cathode and an anode of the Zener diode.

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.