The operation that results is a linear combination of incoming signals to generate the output signal. The sign appearing alongside each input to the summing point indicates the sign of that signal as it appears in the output.
Electric circuit theory includes the study of all aspects of electric circuits, including analysis, design, and application. In electric circuit theory the fundamental quantities are the potential differences (voltages) in volts between various points, the electric currents in amperes flowing in the several paths, and the parameters in ohms or mhos which describe the passive elements. Other important circuit quantities such as power, energy, and time constants may be calculated from the fundamental variables. For a discussion of these parameters.
Because most signals in the real world are analog but digital computers work on discretizations, it is necessary to convert between digital and analog signals. As mentioned above, this is done through digital-to-analog and analog-to-digital converters. Most approaches to digital-to-analog conversion use summers, where the voltages representing the digital bits are applied to input resistors, either directly or indirectly through switches gated on by the digital bits which change the input resistance fed by a dc source.
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.