An apparatus comprising: a signal amplifier having a signal amplifier signal output (V out1); a first filter capacitor; a buffer amplifier having a buffer amplifier input and a buffer amplifier output; and a switching network (151, 152, 153, 156), wherein said first filter capacitor has first and second terminals, said second terminal being connected to a power rail, wherein said switching network (151, 152, 153, 156) is configured, during a first time period: - to connect said signal amplifier signal output (V out1) to said buffer amplifier input by a first direct current path comprising a first switch and said buffer amplifier output to said first terminal of said first filter capacitor by a second direct current path comprising a second switch, the first switch and second switch being closed, and wherein said switching network (151, 152, 153, 156) is configured, during a second time period: - to disconnect the first direct current path and second direct current path by the first switch and second switch being open, and - to connect said signal amplifier signal output (V out1) directly to said first terminal of said first filter capacitor by a third direct current path comprising a third switch, the third switch being closed, characterized in said switching network (151, 152, 153, 156) being further configured, during a third time period: - to disconnect the third direct current path by the third switch being open, and - to connect said signal amplifier signal output (V out1) to said first terminal of said first filter capacitor through a resistor on a fourth current path comprising a fourth switch, the fourth switch being closed, wherein said first time period precedes said second time period and said second time period precedes said third time period; wherein the first switch, second switch and fourth switch are controlled by a first control signal (S 3), wherein the first switch and second switch are opened when the fourth switch is closed, and vice versa; wherein the third switch is controlled by a second control signal (S 4). a signal amplifier having a signal amplifier signal output (V out1); a first filter capacitor; a buffer amplifier having a buffer amplifier input and a buffer amplifier output; and a switching network (151, 152, 153, 156), wherein said first filter capacitor has first and second terminals, said second terminal being connected to a power rail, wherein said switching network (151, 152, 153, 156) is configured, during a first time period: - to connect said signal amplifier signal output (V out1) to said buffer amplifier input by a first direct current path comprising a first switch and said buffer amplifier output to said first terminal of said first filter capacitor by a second direct current path comprising a second switch, the first switch and second switch being closed, and - to connect said signal amplifier signal output (V out1) to said buffer amplifier input by a first direct current path comprising a first switch and said buffer amplifier output to said first terminal of said first filter capacitor by a second direct current path comprising a second switch, the first switch and second switch being closed, and wherein said switching network (151, 152, 153, 156) is configured, during a second time period: - to disconnect the first direct current path and second direct current path by the first switch and second switch being open, and - to connect said signal amplifier signal output (V out1) directly to said first terminal of said first filter capacitor by a third direct current path comprising a third switch, the third switch being closed, - to disconnect the first direct current path and second direct current path by the first switch and second switch being open, and - to connect said signal amplifier signal output (V out1) directly to said first terminal of said first filter capacitor by a third direct current path comprising a third switch, the third switch being closed, characterized in said switching network (151, 152, 153, 156) being further configured, during a third time period: - to disconnect the third direct current path by the third switch being open, and - to connect said signal amplifier signal output (V out1) to said first terminal of said first filter capacitor through a resistor on a fourth current path comprising a fourth switch, the fourth switch being closed, - to disconnect the third direct current path by the third switch being open, and - to connect said signal amplifier signal output (V out1) to said first terminal of said first filter capacitor through a resistor on a fourth current path comprising a fourth switch, the fourth switch being closed, wherein said first time period precedes said second time period and said second time period precedes said third time period; wherein the first switch, second switch and fourth switch are controlled by a first control signal (S 3), wherein the first switch and second switch are opened when the fourth switch is closed, and vice versa; wherein the third switch is controlled by a second control signal (S 4).