A Darlington pair sensor is disclosed. The Darlington pair sensor has an amplifying/horizontal bipolar junction transistor (BJT) and a sensing/vertical BJT and can be used as a biosensor.

The amplifying bipolar junction transistor (BJT) is horizontally disposed on a substrate. The amplifying BJT has a horizontal emitter, a horizontal base, a horizontal collector, and a common extrinsic base/collector. The common extrinsic base/collector is an extrinsic base for the amplifying BJT.

The sensing BJT has a vertical orientation with respect to the amplifying BJT. The sensing BJT has a vertical emitter, a vertical base, an extrinsic vertical base, and the common extrinsic base/collector (in common with the amplifying BJT). The common extrinsic base/collector acts as the sensing BJT collector. The extrinsic vertical base is separated into a left extrinsic vertical base and a right extrinsic vertical base giving the sensing BJT has two separated (dual) bases, a sensing base and a control base.

The Darlington pair sensor has high in-situ signal amplification with low noise and uses substrate space effectively.

An output circuit of an amplifier which does not change power consumption. Since the output circuit of the amplifier does not flow, to a power supply circuit, a current correlated to a signal, the output circuit is not affected by the power supply circuit. The output circuit of the amplifier is provided with: a three-terminal amplifying element having an input terminal, an output terminal, and a common terminal; and a constant current circuit which is connected to the common terminal, and which flows a substantially constant current to the three-terminal amplifying element. The output terminal is grounded, and amplified output is taken out between the output terminal, and a contact point between the common terminal and the constant current circuit. Thus, the consumption current of the output circuit of the amplifier is merely the current flowing in the constant current circuit.

A Darlington pair sensor is disclosed. The Darlington pair sensor has an amplifying/horizontal bipolar junction transistor (BJT) and a sensing/vertical BJT and can be used as a biosensor. The amplifying bipolar junction transistor (BJT) is horizontally disposed on a substrate. The amplifying BJT has a horizontal emitter, a horizontal base, a horizontal collector, and a common extrinsic base/collector. The common extrinsic base/collector is an extrinsic base for the amplifying BJT. The sensing BJT has a vertical orientation with respect to the amplifying BJT. The sensing BJT has a vertical emitter, a vertical base, an extrinsic vertical base, and the common extrinsic base/collector (in common with the amplifying BJT). The common extrinsic base/collector acts as the sensing BJT collector. The extrinsic vertical base is separated into a left extrinsic vertical base and a right extrinsic vertical base giving the sensing BJT has two separated (dual) bases, a sensing base and a control base. The Darlington pair sensor has high in-situ signal amplification with low noise and uses substrate space effectively.