My question is very basic one, but thought of asking here to clarify.
In asynchronous counter the output of Flip Flop is given as input to other Flip Flop as clock, where as in synchronous counter the output of Flip Flop is given as direct input to other Flip Flop. So in both cases the next Flip Flop has to wait until previous output of Flip Flop is available.
Can someone explain how synchronous counter has less propagation delay than asynchronous?
Electrical – How propagation delay of synchronous counter is less than asynchronous counter
counterflipflopsynchronous
Related Solutions
Internally, a flip-flop (the term includes everything from simple D latches to more complex edge-triggered J-K master-slave flip-flops) is an asynchronous state machine. It is created by combining ordinary logic gates with feedback.
For example, here's one way to construct a master-slave D flip-flop:
simulate this circuit – Schematic created using CircuitLab
Each of the internal sections is a simple set-reset latch with an enable input. Because the two enables are driven with opposite levels of the "CLK" input, the output can only change state on its rising edge.
Note that while this design is conceptually simple to understand, it is NOT typical of how commercial chips (e.g., 7400-series) are constructed internally. If you study SSI/MSI databooks (the older TI books were especially good), you'll see several other ways to construct flip-flops from gates.
Once you have an edge-triggered flip-flop of any sort, you can use it (or multiple copies of it) to create synchronous state machines that only make transitions on clock edges.
The first one is not master-slave; you would have to cascade two copies of that circuit (with the clock inverted between them) to get the same functionality as the second circuit, which is indeed a master-slave (edge-triggered) flip-flop.
Best Answer
In every Flip-Flop there is the clock-to-Q delay.
In a synchronous counter all the outputs are updated with a single clock to Q delay.
In an a-synchronous counter the first FF updates after one clock to Q delay. The second one can only change after the first one has changed so it updated in two clock to Q delays. The third one needs three clock to Q delays etc.