  While digital electronics has become entirely ubiquitous in today's world and
appears in the limelight, analogue electronics is still playing a crucial role
in many devices and applications. Current analogue circuits are mostly
manufactured using silicon as active material, but the ever present demand for
improved performance, new devices and flexible integration has - similar to
their digital counterparts - pushed for research into alternative materials. In
recent years two-dimensional materials have received considerable research
interest, fitting their promising properties for future electronics. In this
work we demonstrate an operational amplifier - a basic building block of
analogue electronics - using a two-dimensional semiconductor, namely molybdenum
disulfide, as active material. Our device is capable of stable operation with
good performance, and we demonstrate its use in feedback circuits such as
inverting amplifiers, integrators, log amplifiers, and transimpedance
amplifiers.
