The invention describes a method of performing analog-to-digital conversion on an input signal (Pin) within a range (R1) using a sigma-delta modulator (1) comprising a feedback digital-to-analog conversion arrangement (12, 120), which method comprises the steps of: obtaining an amplitude estimate (E1, E2, E3, E4) of the input signal (Pin); defining a subsequent subrange (R2, R3, R4) on the basis of the amplitude estimate (E1, E2, E3); and adjusting operation parameters of the feedback digital-to-analog conversion arrangement (12, 120) on the basis of the subsequent subrange (R2, R3, R4); whereby the method steps are repeated a predefined number of iterations (N). The invention further describes a sigma-delta modulator (1), an analog-to-digital converter (50), and a monitoring device (5) for monitoring an analog input signal (Pin).