22 a so as to provide a negative feedback voltage as a function of the output averaged over time of comparator 22 a in operation comparator 22 a performs an analog comparison of analog input 16 a and the negative feedback voltage and provides a logic_ 1 value when analog input 16 a is higher than the negative feedback voltage and a logic_ 0 value when analog input 16 a is lower than the negative feedback voltage in adc 12 b the feedback network 24 b is connected to the non inverting input of comparator 22 b so as to provide a positive feedback voltage as a function of the output averaged over time of comparator 22 b in operation comparator 22 b performs an analog comparison of analog input 16 b and the positive feedback voltage and provides a logic_ 1 value when analog input 16 b is lower than the positive feedback voltage and a logic_ 0 value when analog input 16 b is higher than the positive feedback voltage in accordance with our invention a suitable feedback network 24 x illustrated in fig3 comprises an averager 26 x a low pass filter 28 x and a digital to analog converter u201c dac u201d 30 x in accordance with our invention averager 26 a b is adapted to monitor the respective output 18.