A circuit , comprising: - a differential stage having a first input node and a second input node , the differential stage having a first output node and a second output node configured to provide a differential output signal (V diff ) therebetween, - an analog-to-digital converter coupled to the first and second output nodes of the differential stage , the analog-to-digital converter configured to provide an output signal (Vout) which is a function of the differential output signal from the differential stage , - a multiplexer comprising a first input terminal and a second input terminal configured to receive a differential input signal (DV) therebetween as well as a test switch (sw3) switchable between a conductive state and a non-conductive state, wherein the test switch (sw3) in the conductive state couples the first input node and the second input node of the differential stage , characterised by - test signal injection circuitry (144, 1440, sw4; V bg1 /nR, sw4) activatable (sw4) to force (1404; 141, 142) a differential current through the differential stage , wherein the circuit is selectively switchable between: - an operational mode, with said test switch (sw3) in the non-conductive state and the multiplexer configured (sw1, sw2) to transfer said differential input signal (DV) to the first input node and the second input node of the differential stage and said test signal injection circuitry (144, 1440, sw4; V bg1 /nR, sw4) inactive, wherein said differential output signal (V diff ) from the differential stage comprises a replica of said differential input signal (DV) ; - a self-test mode, with said test switch (sw3) in the conductive state and said test signal injection circuitry (144, 1440, sw4; V bg1 /nR, sw4) active, wherein said differential output signal (V diff ) from the differential stage is a function of said differential current forced through the differential stage by said test signal injection circuitry (144, 1440, sw4; V bg1 /nR, sw4). - a differential stage having a first input node and a second input node , the differential stage having a first output node and a second output node configured to provide a differential output signal (V diff ) therebetween, - an analog-to-digital converter coupled to the first and second output nodes of the differential stage , the analog-to-digital converter configured to provide an output signal (Vout) which is a function of the differential output signal from the differential stage , - a multiplexer comprising a first input terminal and a second input terminal configured to receive a differential input signal (DV) therebetween as well as a test switch (sw3) switchable between a conductive state and a non-conductive state, wherein the test switch (sw3) in the conductive state couples the first input node and the second input node of the differential stage , characterised by - test signal injection circuitry (144, 1440, sw4; V bg1 /nR, sw4) activatable (sw4) to force (1404; 141, 142) a differential current through the differential stage , - an operational mode, with said test switch (sw3) in the non-conductive state and the multiplexer configured (sw1, sw2) to transfer said differential input signal (DV) to the first input node and the second input node of the differential stage and said test signal injection circuitry (144, 1440, sw4; V bg1 /nR, sw4) inactive, wherein said differential output signal (V diff ) from the differential stage comprises a replica of said differential input signal (DV) ; - a self-test mode, with said test switch (sw3) in the conductive state and said test signal injection circuitry (144, 1440, sw4; V bg1 /nR, sw4) active, wherein said differential output signal (V diff ) from the differential stage is a function of said differential current forced through the differential stage by said test signal injection circuitry (144, 1440, sw4; V bg1 /nR, sw4). <EOS>