ANORDNING FOR DIGITALISERING AV EN ANALOG SIGNAL, SAMT ANVENDNING AV NEMNDA ANORDNING VID EN APPARAT FOR ELEKTROCARDIOGRAFI

A device for digitizing an analog signal whose mean value is constant, comprising a delta modulator (3) which is arranged to sample the signal during successive time intervals, each of which has a duration which corresponds to n pulses of a clock pulse generator (11), and to supply m (m < n) pulses per time interval DELTA T, m being dependent on the difference between the values of the signal at the beginning (T) and at the end (T + DELTA T) of the interval. The clocked output of the delta modulator (3) is applied together with the clock pulses to a bidirectional counter (5) arranged to count in one direction or the other in response to the corresponding presence or absence of a modulator output pulse during a clock pulse, and the running total count is applied as a digital input value to a correction circuit (7) which is constructed as a digital high-pass filter (Figure 3) in order to remove error signals which are added to the signal due to inaccuracies of the delta modulator, by forming the progressive mean value S(T) of the counter output signal and subtracting this from the counter output S(T + DELTA T).