A single-stage differential operational amplifier comprising: an input stage formed by a pair of input transistors (31, 32), having control terminals connected to a first and respectively second input (IN+, IN-) of said operational amplifier, first conduction terminals coupled to a first and respectively second output (OUT-, OUT+) of said operational amplifier and second conduction terminals designed to receive a biasing current (I b); an output stage formed by a pair of output transistors (34, 35), in diode configuration, having control terminals, each designed to be coupled to a corresponding first conduction terminal, connected to the first and respectively second output (OUT -, OUT +) of said operational amplifier, and second conduction terminals connected to a reference line (gnd), characterized by further comprising: a coupling stage interposed between the first conduction terminals of said output transistors (34, 35) and said first and respectively second output (OUT-, OUT+) and configured to define a small-signal gain value of said operational amplifier; wherein said coupling stage comprises a first and a second coupling transistor (37, 38), having control terminals connected together for receiving a first biasing voltage (V b1), first conduction terminals connected to a respective one of said first and second outputs (OUT-, OUT+) and second conduction terminals coupled to the first conduction terminals of said output transistors (34, 35) and directly connected together by a connection line. an input stage formed by a pair of input transistors (31, 32), having control terminals connected to a first and respectively second input (IN+, IN-) of said operational amplifier, first conduction terminals coupled to a first and respectively second output (OUT-, OUT+) of said operational amplifier and second conduction terminals designed to receive a biasing current (I b); an output stage formed by a pair of output transistors (34, 35), in diode configuration, having control terminals, each designed to be coupled to a corresponding first conduction terminal, connected to the first and respectively second output (OUT -, OUT +) of said operational amplifier, and second conduction terminals connected to a reference line (gnd), characterized by further comprising: a coupling stage interposed between the first conduction terminals of said output transistors (34, 35) and said first and respectively second output (OUT-, OUT+) and configured to define a small-signal gain value of said operational amplifier; wherein said coupling stage comprises a first and a second coupling transistor (37, 38), having control terminals connected together for receiving a first biasing voltage (V b1), first conduction terminals connected to a respective one of said first and second outputs (OUT-, OUT+) and second conduction terminals coupled to the first conduction terminals of said output transistors (34, 35) and directly connected together by a connection line. a coupling stage interposed between the first conduction terminals of said output transistors (34, 35) and said first and respectively second output (OUT-, OUT+) and configured to define a small-signal gain value of said operational amplifier; wherein said coupling stage comprises a first and a second coupling transistor (37, 38), having control terminals connected together for receiving a first biasing voltage (V b1), first conduction terminals connected to a respective one of said first and second outputs (OUT-, OUT+) and second conduction terminals coupled to the first conduction terminals of said output transistors (34, 35) and directly connected together by a connection line.