Abstract: The invention provides a transformer suitable for use in a high frequency semiconductor device, and the transformer can be formed without the use of a conventional core and coils by forming at least two spiral inductors selected from a plurality of spiral inductors on a semiconductor substrate so as to overlap each other substantially in the vertical direction with an interlayer insulator interposed in between.

Abstract: A feedback amplifier includes an input terminal where an input voltage is detected from an input current; an amplifier circuit which amplifies the input voltage to generate an output signal; a first output terminal from which the output signal is outputted; and a feedback circuit. The feedback circuit includes a feedback resistor connected between the input terminal and the first output terminal; and a diode which connected in parallel to the feedback resistor. The output signal is feedback-controlled in response to the product of the input current and the impedance of the feedback circuit.