Digital systems
Electric systems

Astatic systems can be found in many domains, e.g. in electrical engineering. On the Figure is shown, where the integration occurs by charging and discharging of capacitor, supplied by a constant current source. During the charging, an electric charge is continuously fed to the capacitor. The charging velocity (current) does not depend on time nor actual capacitor voltage. The capacitor voltage u2 increases proportionally to the total amount of stored charge. Discharging is an opposite process of decreasing capacitor charge. If the absolute value of charging and discharging current is equal, the system is linear, if these values differ; the system is asymmetric as above, i.e. nonlinear. Theoretically, the capacitor voltage is unlimited up to infinity. In practice, the saturation will apply as well due to voltage limitations of the supply.

Notice: In the circuit theory point of view, this circuit is linear; the only nonlinearity is due to current source limitation, which is, in our particular case, able to supply only two values of output current. It is similar to hydraulic system mentioned above, where the nonlinearity consists of input valves and constant flux. The system properties, like the (non)linearity, can change, if we regard the system only as some "internal subsystem", or if we include actuators and sensors as well, causing additional nonlinearity or dynamics.

Fig. 8.5: Example of astatic system