A circuit comprising: an input terminal configured to receive an input-signal; an output terminal configured to provide an output-signal; a reference circuit comprising: a first output terminal configured to provide a first-reference-signal; a second output terminal configured to provide a second-reference-signal; and a third output terminal configured to provide a third-reference-signal. A comparator-block configured to compare a comparator-input-voltage-signal representative of signalling received at the input terminal with: (i) the first-reference-signal, (ii) the second-reference-signal and (iii) the third-reference-signal in order to generate a comparison-signal. A control-block configured to set the output-signal as one of at least two voltage levels based on the comparison-signal; and an input-control-circuit configured to apply a feedback-control-signal to the input-terminal based on the comparison-signal.