An analog-to-digital converter for an imager, said analog-to-digital converter comprising: a sensing circuit comprising: a first circuit branch for inputting a reset signal voltage and creating a reset current; and a second circuit branch for inputting a pixel signal voltage and creating a pixel current; characterised; in that said sensing circuit further comprises an adjustment branch for creating an adjustment current from a reference voltage using sigma-delta modulation of a resistance in said adjustment branch, said adjustment current being combined with the reset current, wherein said adjustment branch is connected to a comparator for comparing the combined current to the pixel current, thereby adjusting the adjustment current so as to get the combined current equal to the pixel current; and in that the analog-digital-converter further comprises a counter for counting a number of times the resistance is sigma-delta modulated during a predetermined number of clock cycles and outputting a digital code corresponding to a difference between the pixel signal voltage and the reset signal voltage. a sensing circuit comprising: a first circuit branch for inputting a reset signal voltage and creating a reset current; and a second circuit branch for inputting a pixel signal voltage and creating a pixel current; characterised; in that said sensing circuit further comprises an adjustment branch for creating an adjustment current from a reference voltage using sigma-delta modulation of a resistance in said adjustment branch, said adjustment current being combined with the reset current, wherein said adjustment branch is connected to a comparator for comparing the combined current to the pixel current, thereby adjusting the adjustment current so as to get the combined current equal to the pixel current; and a first circuit branch for inputting a reset signal voltage and creating a reset current; and a second circuit branch for inputting a pixel signal voltage and creating a pixel current; characterised; in that said sensing circuit further comprises an adjustment branch for creating an adjustment current from a reference voltage using sigma-delta modulation of a resistance in said adjustment branch, said adjustment current being combined with the reset current, wherein said adjustment branch is connected to a comparator for comparing the combined current to the pixel current, thereby adjusting the adjustment current so as to get the combined current equal to the pixel current; and in that said sensing circuit further comprises an adjustment branch for creating an adjustment current from a reference voltage using sigma-delta modulation of a resistance in said adjustment branch, said adjustment current being combined with the reset current, wherein said adjustment branch is connected to a comparator for comparing the combined current to the pixel current, thereby adjusting the adjustment current so as to get the combined current equal to the pixel current; and in that the analog-digital-converter further comprises a counter for counting a number of times the resistance is sigma-delta modulated during a predetermined number of clock cycles and outputting a digital code corresponding to a difference between the pixel signal voltage and the reset signal voltage.