14-12-2012, 04:55 PM
Circuit Design Using Logical Gates
Circuit Design.ppt (Size: 1.48 MB / Downloads: 35)
Logic Circuit
Combinational Circuit
The output of a combinational circuit depends on its present input only.
Sequential Circuit
The output of a sequential circuit not only depends on its present input but also depends on the state of the circuit.
So for that, its have Memory element.
This Memory Element called as Flip-Flop or Latch
Combinational logic circuits
The output of a combinational circuit depends on its present input only.
Gates are building blocks of combinational circuit.
Sequential logic circuits
The output of a sequential circuit not only depends on its present input but also depends on the state of the circuit.
In this past history is provided by feedback from output to input
Latch
Latches are the simplest kind of sequential circuit has only two states .
Latch is one type of Flip-Flop.
A Binary storage Device which is storing 1 bit information is known as Flip-Flop.
Latch a memory cell ,which is capable of storing one bit of information, ie , logic 1 or 0 .
GATED LATCH [Clocked Flip-flop]
The Gated RS Latch
A gated Latch require one extra input that is, ENABLE input. This ENABLE input may be a clock so, gated SR-Latch is also called a clocked SR Latch/ Synchronous SR Latch.
Its S & R inputs will observe only when the ENABLE is HIGH, when En high (enable true), the signals can pass through the input gates, then immediately reproduce on the (Q,Q’) output.
When the ENABLE low (enable false) it is remains in the state it was left the last time E was high., or no change of a state can take place.
GATED D-LATCH
Drawback of RS Latch is when both input is 1, we cannot determinate the output. To eliminate this undesirable condition, D-Latch is introduce.
This D-Latch has two input
D [DATA]
C [Control]
D input goes directly to the S input & its complement is applied to the R input.
If D=1 Q=1 placing circuit in the SET State
If D=0 Q=0 placing circuit in the RESET State
In the D-Latch binary information present of the data input D Latch is transferred to the Q output, when the control input is enabled, So its called Transparent Latch
Flip Flop
A Binary storage Device which is storing 1 bit information is known as Flip-Flop.
Latch is build from the gates and, Flip-Flop is build from the latch.
Two Characteristic
Flip-Flop is a bistable device, that is circuit with only two state 0 &1.
Flip Flop has two output signals, and one of which is the complement of other.
JK FLIP-FLOP
The J-K Flip-Flop is very versatile and also most widely used.
J-K Flip-Flop is used to solve the problem of indeterminate state of RS Flip-Flop.
Inputs J and K behave like inputs S and R to set and reset the flip flop , respectively .When J=K=1 , the flip flop output is toggle, i.e switches to its complement state ; if Q = 0 , it switches to Q=1 and vice versa
When clock is Low or falling Edge (-VE Edge) ,
No change in output with the input
When clock is high or raising Edge (+VE Edge)
case1 : When J=0 and K=0 No change to the output
Case2 : When J=1 and K=0 Output set (ie Q=1)
case3 : When J=0 and K=1 Output Reset (ie Q=0)
case4 : When J=1 and K=1 Output is toggled (ie When Qn =1 then Q’ = 0)
SHIFT REGISTER
Flip-Flop can store only 1 bit of data, either 0 or 1
Register is group of flip-flop, each flip-flop is capable of storing 1 bit information.
So, Register consist group of n flip-flop capable of storing n bits of binary information.
A Register that allow each flip-flop to shift its stored information to its neighbor is called Shift-Register.
In Shift Register group of flip-flop connected in a chain so, that the output from one flip-flop becomes the input of next flip-flop.