Asynchronous circuit

Asynchronous circuits are electrical circuits that operate in contrast to synchronous circuits without a global clock. In a purely synchronous circuit, the clock signal is applied to all flip- flops in parallel, ie, all flip -flop switch at the same time. For asynchronous circuits all the flip -flops are not directly connected to the same clock signal. The clock signal of a flip -flop may eg the output of a previous flip -flops or it can be the output of a logic gate to be.

This distinction is not relevant for calculating units (English datapath ) - these generally require no clock signal - but only for control units (English controlpath ).

Control units must be able to save its internal state. In asynchronous circuits this is either also ensured by integrated signal memory in the form of flip- flops or by the signal level of the incoming and outgoing signal lines from external latches. A distinction is made between external signals that are controlled by the environment and local signals that are controlled by the circuit itself.

Changes in the signal state can be done independently or concurrently with asynchronous circuits. On a theoretical level, this can be described by Signal Transition Graphs ( STGS ), a special form of Petri nets.

In the practical circuit design using asynchronous circuit technology in the past has increasingly lost importance. In a synchronous circuit design, the time for the signal delay and the switching of the flip-flops can be mostly well determined or estimated. With asynchronous circuit design is usually possible only with very great effort, since subsequent switching operations each on the exact switching time of the previous component may be dependent. Furthermore, in the purely asynchronous circuits the risk of design errors and switching errors, as for the components in actual operation usually only a minimum switching time and maximum switching time is specified and the actual switching time is somewhere within the specified range. Highly complex circuits are built today exclusively as a purely synchronous circuits.

Applications

An example of an asynchronous processor architecture is the AMULET processor based on the ARM architecture.