Signals may have an
- analogue,
- digital or
- binary
character. In addition, they may
- have a continuous value, i.e. the signal parameter can take on all values within an interval;
- have a discrete value, i.e. the signal parameter, e.g. a DC voltage, may take on certain discrete values (or non-overlapping value ranges);
- be kept constant over time, e.g. the signal parameter (signal voltage) is defined at any desired point throughout the duration of the signal;
- be time discrete, i.e. the signal character is defined only at clearly defined discrete times (or a sequence of discrete time intervals).
Accordingly, four types of signal form are possible:
- value constant and constant over time,
- value constant and discrete over time,
- value discrete and constant over time,
- value discrete and discrete over time (DIN 19 225).