An amplifier with adjustable gain including a plurality of differential amplifiers and an output stage circuit is provided. Each of the differential amplifiers has at least one differential pair, two current terminals of each of the differential pairs are coupled by a connection structure, and the connection structure provides a negative feedback resistance. The differential amplifiers commonly receive a differential input signal pair, and output terminals of the differential amplifiers are coupled together. The output stage circuit inverts a voltage on the output terminals of the differential amplifiers to generate an output voltage. A direct current gain of the amplifier with adjustable gain is determined by adjusting at least one of working numbers of the differential amplifiers and the differential pairs.

The present invention is directed to electrical circuits and techniques thereof. More specifically, an embodiment of the present invention provides a line driver with transistors directly coupled to the ground, and a bias voltage is coupled common mode resistors of the line driver. There are other embodiments as well.

A detection device includes a driving circuit which drives a physical quantity transducer, a detection circuit which detects a desired signal, a power-supply terminal into which a power-supply voltage is input, a regulator circuit which performs a voltage adjustment of stepping down the power-supply voltage from the power-supply terminal, and supplies a regulated power-supply voltage obtained by the voltage adjustment to the driving circuit and the detection circuit as an operating power-supply voltage, and a buffer circuit which is supplied with the power-supply voltage, receives a drive signal from the driving circuit, and outputs an amplified drive signal in which an amplitude of the drive signal increases to the physical quantity transducer.