BOOLEAN ALGEBRA AND LOGIC GATES
Basically there are two types of signals in electronics,
The usual advantages of digital circuits when compared to analog circuits are:
Digital systems interface well with computers and are easy to control with software. New features can often be added to a digital system without changing hardware. Often this can be done outside of the factory by updating the product's software. So, the product's design errors can be corrected after the product is in a customer's hands.
Information storage can be easier in digital systems than in analog ones. The noise-immunity of digital systems permits data to be stored and retrieved without degradation. In an analog system, noise from aging and wear degrade the information stored. In a digital system, as long as the total noise is below a certain level, the information can be recovered perfectly.
One of the primary advantages of digital electronics is its robustness. Digital electronics are robust because if the noise is less than the noise margin then the system performs as if there were no noise at all. Therefore, digital signals can be regenerated to achieve lossless data transmission, within certain limits. Analog signal transmission and processing, by contrast, always introduces noise.
In some cases, digital circuits use more energy than analog circuits to accomplish the same tasks, thus producing more heat as well. In portable or battery-powered systems this can limit use of digital systems.
For example, battery-powered cellular telephones often use a low-power analog front-end to amplify and tune in the radio signals from the base station. However, a base station has grid power and can use power-hungry, but very flexible software radios. Such base stations can be easily reprogrammed to process the signals used in new cellular standards.
Digital circuits are sometimes more expensive, especially in small quantities.The sensed world is analog, and signals from this world are analog quantities.
For example, light, temperature, sound, electrical conductivity, electric and magnetic fields are analog. Most useful digital systems must translate from continuous analog signals to discrete digital signals. This causes quantization errors.
error can be reduced if the system stores enough digital data to represent the
signal to the desired degree of fidelity. The Nyquist-Shannon sampling theorem
provides an important guideline as to how much digital data is needed to
accurately portray a given analog signal.