History
The first electronic flip-flop was invented in 1918 by William Eccles and F. W. Jordan.[1][2] It was initially called the Eccles–Jordan trigger circuit and consisted of two active elements (radio-tubes). The name flip-flop was later derived from the sound produced on a speaker connected to one of the back coupled amplifiers outputs during the trigger process within the circuit (as such, it may be considered a case of onomatopoeia).[citation needed] This original electronic flip-flop—a simple two-input bistable circuit without any dedicated clock (or even gate) signal, was transparent, and thus a device that would be labeled as a "latch" in many circles today.
Implementation
Flip-flops can be either simple (transparent) or clocked. Simple flip-flops can be built around a pair of cross-coupled inverting elements: vacuum tubes, bipolar transistors, field effect transistors, inverters, and inverting logic gates have all been used in practical circuits — perhaps augmented by some gating mechanism (an enable/disable input). The more advanced clocked (or non-transparent) devices are specially designed for synchronous (time-discrete) systems; such devices therefore ignore its inputs except at the transition of a dedicated clock signal (known as clocking, pulsing, or strobing). This causes the flip-flop to either change or retain its output signal based upon the values of the input signals at the transition. Some flip-flops change output on the rising edge of the clock, others on the falling edge.
Clocked flip-flops are typically implemented as master-slave devices[3] where two basic flip-flops (plus some additional logic) collaborate to make it insensitive to spikes and noise between the short clock transitions; they nevertheless also often include asynchronous clear or set inputs which may be used to change the current output independent of the clock.
Flip-flops can be further divided into types that have found common applicability in both asynchronous and clocked sequential systems: the SR ("set-reset"), D ("data" or "delay"[4]), T ("toggle"), and JK types are the common ones; all of which may be synthesized from (most) other types by a few logic gates. The behavior of a particular type can be described by what is termed the characteristic equation, which derives the "next" (i.e., after the next clock pulse) output, Qnext, in terms of the input signal(s) and/or the current output, Q. next
sumber: http://en.wikipedia.org/wiki/Flip-flop_(electronics)
