Analog/digital signals and digital advantages

Analog and digital signal

• Analog signal: a signal that varies continuously with time and can take any value within a range. Example: the voltage from a microphone, output of a thermocouple, a sine wave $v = V_m \sin \omega t$.
• Digital signal: a signal that takes only a finite number of discrete values, usually two levels (HIGH = 1, LOW = 0), and changes in steps. Example: the clock pulse in a computer, the output of a TTL gate (0 V / +5 V).

 Analog                 Digital
   .-.     .-.           __    __    __
  /   \   /   \         |  |  |  |  |  |
 /     \ /     \     ___|  |__|  |__|  |__
        '              t ->

Advantages of digital systems over analog systems

1. Noise immunity: only two levels need to be told apart, so small noise does not change the information.
2. Accuracy and precision: accuracy can be increased simply by using more bits; analog accuracy is limited by component tolerance.
3. Easy storage: digital data can be stored for a long time in memories (RAM, ROM, flash, disks) without degradation.
4. Programmability: the operation of a digital system can be changed by software (e.g. microprocessors).
5. Easy design: design uses switching (Boolean) algebra; exact voltage values are not important.
6. Integration: many gates can be placed on one IC chip, so systems are small, cheap and reliable.
7. Easy processing and transmission: data can be encrypted, compressed, error-checked and copied without loss.
8. Less effect of temperature and ageing on circuit behaviour.