The analogue to digital convertor (ADC) converts an analogue signal in an A/D conversion unit. The A/D converted data values are stored in a first register (3). A second register (4) receives the data in the first register (3) via a first switch over device (6). A comparator (5) compares the data values in the first register (3) and the data values in the second register (4). On the basis of the results of the comparison, the switch over device (6) is opened or closed. The convertor may have a second switch over device (8), provided in each of a number of channels. One of the analogue signals in the channels is input into the A/d conversion unit (2). A selector (7) outputs a selection signal, corresponding to a selected channel, to the second switch over device (8) and the first register (3). The first register (3) has memory regions which correspond to the channels. The second register (4) stores a max. or a min. data value of the converted data of all channels.
