An active pixel sensor imaging system comprising: - a plurality of active pixel sensor circuits arranged into an array of rows and columns, and at least one of said active pixel sensor circuits being connected to a supply line and a column line and operable to generate a voltage output through the column line corresponding to a detected light intensity, the plurality of active pixel sensor circuits being connected through the column line to a current generator so as to form in combination with a source-follower transistor of the active pixel sensor circuits a source follower; - a current sensing circuit, located external to the plurality of active pixel sensor circuits and connected to the supply line, the current sensing circuit being implemented as a current mirror for sensing a current through the source-follower transistor; and - a feedback circuit, located external to the plurality of active pixel sensor circuits, the feedback circuit having an output connected to the column line and to the current generator, and an input connected to the current sensing circuit, the feedback circuit comprising a plurality of transistors (M6 to M13) and a reference current source (IREF) arranged to form a classAB-stage current mirror providing an output current to the output connected to the column line, wherein the classAB-stage current mirror comprises a push-pull current mirror stage where the ratio of a first pair of transistors (M10, M12) determines the gain for currents above the reference current (IREF) and the ratio of a second pair of transistors (M11, M13) determines the gain for currents below the reference current (IREF), and a third pair of transistors (M8, M9) connected to the first and second pair of transistors (M10 to M13) and arranged to control the quiescent current of the class AB-stage current mirror according to a Monticelli bias scheme. - a plurality of active pixel sensor circuits arranged into an array of rows and columns, and at least one of said active pixel sensor circuits being connected to a supply line and a column line and operable to generate a voltage output through the column line corresponding to a detected light intensity, the plurality of active pixel sensor circuits being connected through the column line to a current generator so as to form in combination with a source-follower transistor of the active pixel sensor circuits a source follower; - a current sensing circuit, located external to the plurality of active pixel sensor circuits and connected to the supply line, the current sensing circuit being implemented as a current mirror for sensing a current through the source-follower transistor; and - a feedback circuit, located external to the plurality of active pixel sensor circuits, the feedback circuit having an output connected to the column line and to the current generator, and an input connected to the current sensing circuit, the feedback circuit comprising a plurality of transistors (M6 to M13) and a reference current source (IREF) arranged to form a classAB-stage current mirror providing an output current to the output connected to the column line, wherein the classAB-stage current mirror comprises a push-pull current mirror stage where the ratio of a first pair of transistors (M10, M12) determines the gain for currents above the reference current (IREF) and the ratio of a second pair of transistors (M11, M13) determines the gain for currents below the reference current (IREF), and a third pair of transistors (M8, M9) connected to the first and second pair of transistors (M10 to M13) and arranged to control the quiescent current of the class AB-stage current mirror according to a Monticelli bias scheme.