**Digital circuits** are electric circuits based on a number of discrete voltage levels. In most cases there are two voltage levels: one near to zero volts and one at a higher level depending on the supply voltage in use. These two levels are often represented as L and H.

## Levels

Examples of binary logic levels:

Technology | L voltage | H voltage | Notes |
---|---|---|---|

CMOS | 0V to VCC/2 | VCC/2 to VCC | VCC = supply voltage |

TTL | 0V to 0.8V | 2V to VCC | VCC is 4.75V to 5.25V |

## Construction

It is possible to construct digital circuits in forms other than electronic. In principle, any technology capable of representing two discrete states and performing Boolean operations could be used to build a logic circuit. Hydraulic, pneumatic and mechanical versions of logic gates exist and are used in situations where electricity cannot be used. The first two types are considered under the heading of fluidics. One application of fluidic logic is in military hardware that is likely to be exposed to a nuclear electromagnetic pulse (nuclear EMP, or NEMP) that would destroy any electrical circuits.

## Logic systems

Digital circuits are the most common hardware realisation of Boolean algebra and are the basis of all digital computers. (See also logic gate.)

They can also be used to process digital information without being connected up as a computer. Such circuits are referred to as "random logic".

## Recent developments

Digital circuit technological innovations have benefitted from the discovery of superconductivity. Most recently, attempts are being made to construct optical computing systems capable of processing digital information.

**Related**:

Boolean algebra | Circuit | CMOS | Combinatorial logic | Data strobe encoding | De Morgan's laws | Digital | Electrical network | Electronics | Field effect transistor | Finite state machine | Formal verification | Glitch Ringing | Hardware description language | Instruction pipelining | Integrated circuit | Sequential logic | Logic analyzer | Logic gate | Microelectronics | Multiplexer | Multiplication ALU | NMOS | Programmable logic device | Reconfigurable system | Register | Transistor | Transistor-transistor logic | Transparent latch | Ternary logic | Runt pulse | Transmission line | VHSIC

- Claude E. Shannon : used Boolean algebra for building digital circuits.
- List of electrical Input/Output standards