A convenient graphical representation of input-output behavior of a system, where the signal into the block represents the input and the signal out of the block represents the output. The flow of information (the signal) is unidirectional from the input to the output. The primary use of the block diagram is to portray the interrelationship of distinct parts of the system.
The field of electronic circuits is very broad and there are a very large number of other circuits besides those discussed above. For example, the differential is a key element in operational amplifier design and in biomedical data acquisition devices which must also be interfaced with specialized electronic sensors. Light-emitting and -detecting diodes allow for signals to be transmitted and received at optical frequencies. Liquid crystals are controlled by electronic circuits and are useful in digital watches, flat-panel color television displays, and electronic shutters.
An interconnection of electronic devices, an electronic device being an entity having terminals which is described at its terminals by electromagnetic laws. Most commonly these are voltage-current laws, but others, such as photovoltaic relationships, may occur.
Transistors are basic to the operation of electronic circuits. Bipolar transistors have three terminals, designated as the base B, the collector C, and the emitter E. These terminals connect to two diode junctions, B-C and B-E, these forming back-to-back diodes. The B-E junction is often forward-biased, in which case its voltage is about 0.7 V, while the B-C junction is reverse-biased for linear operation.