What is JK Flip-Flop ? - GeeksforGeeks (2024)

In Digital Electronic flip-flops are widely used for handling binary information. These fundamental building blocks are used to store and manipulate information as per our needs. From the Flipflop family, Jack Kilby flip-flop(JK Flipflop) is versatile and can be used as a basic memory element. It can also store toggle functionality with a diversity of making applications with it. In this article we will see JK flipflop.

What is JK Flip-Flop?

It is one kind of sequential logic circuit which stores binary information in bitwise manner. It consists of two inputs and two outputs. Inputs are Set(J) & Reset(K) and their corresponding outputs are Q and Q’. JK flipflop has two modes of operation which are synchronous mode and asynchronous mode. In synchronous mode, the state will be changed with the clock(clk) signal, and in asynchronous mode, the change of state is independent from its clock signal. Let’s see its diagram structure.

The JK flip flop diagram above represents the basic structure which consists of Clock (CLK), Clear (CLR), and Preset (PR).

Below is the circuit diagram of JK Flip Flop. Two 3-input NAND gates are used in place of the original two 2-input AND gates. The outputs at Q and Q’ are coupled to each gate’s third input. Since the two inputs are now interlocked, the SR flip-flop’s cross-coupling enables the previously invalid condition of (S = “1”, R = “1”) to be employed to perform the “toggle action”.

In a circuit “set”, the bottom NAND gate interrupts the J input coming from the “0” position of Q’. In the “RESET” state, the top NAND gate interrupts the K input coming from the 0 positions of Q. We can use Q and Q’ to control the input because they are always different. The flip flop is toggled according to the truth table when both inputs “J” and “K” are set to 1.

Truth Table of JK Flip Flop

Characteristic Table

A JK flip-flop is a kind of sequential logic circuit that keeps track of binary data. Its characteristic table shows how the output (Qn+1) changes using inputs (J & K) along with the last state (Qn).

Let’s break down the characteristic table. There are four states to understand:

1. J = 0, K = 0 (No Change): Here, the output Q(n+1) stays the same. This means the next state (Q(n+1)) is just like the current one (Qn).
2. J = 0, K = 1 (Reset State): In this case, the next state is reset to 0 (Q(n+1) = 0), no matter what the current state is (Qn).
3. J = 1, K = 0 (Set State): Now, the next state gets set to 1 (Q(n+1) = 1), again, no matter what’s happening in the current state (Qn).
4. J = 1, K = 1 (Toggle State): In this state, the output Q(n+1) toggles. So if the current state is set (Qn = 1), it will change to 0 (Q(n+1) = 0). If it’s reset (Qn = 0), then it flips to 1 (Q(n+1) = 1).

Characteristic Equation: K̅Qn + JQ̅n

Group 1: J̅ K̅Qn + JK̅Qn

Group 2: JK̅Q̅n + JKQ̅n

See Also

JK Flip Flop : Truth table and Block, Circuit & Timing Diagram

Equation: J̅ K̅Qn + JK̅Qn + JK̅Q̅n + JKQ̅n

= (J̅ + J)K̅Qn + JQ̅n(K̅+K) …..(Distribution Law)

= 1.K̅Qn + 1.JQ̅n …..(Compliment Law, J̅ + J = 1 and K̅+K = 1)

= K̅Qn + JQ̅n …..(Identity Law, 1&A = A )

Excitation Table

The excitation table shows us which input combinations we should use for a JK flip-flop to get the output we want.

• X – Don’t Care
• Qn – Current State
• Q(n+1) – Next State
• J and K – Two input values

Here, X for Don’t Care. This means it can be either 0 or 1, & it won’t change how the flip-flop works.

This table guides us on what input values to use so we can move from the current (Qn) to the next state (Q(n+1)).

Let’s look at the transitions

1. From 0 to 0: When the current state is 0 (Qn = 0) and you want the next one to stay 0 (Q(n+1) = 0), then set J = 0 & K can be either 0 or 1, which is shown as X (Don’t Care).
2. From 0 to 1: If the current state is 0 (Qn = 0) but you want the next state to flip to 1 (Q(n+1) = 1), then J should be set to 1 & K = X (doesn’t matter for K).
3. From 1 to 0: When you start with a current state of 1 (Qn = 1) & wish for it to switch to 0 (Q(n+1) = 0), then J should be X and K must be set at 1.
4. From 1 to 1: If you’re at a current state of 1 (Qn = 1) & want it to stay at 1 for the next state (Q(n+1) = 1), then just set J = X and K should be set at 0.

This table is used a lot in circuit design. It helps show the inputs needed to get those desired output transitions.

Applications of JK Flip-Flop

• Counters: Counters are very essential components for the application of frequency dividers and event sequencers where there is a need of storing and propagating the count value. We can design binary synchronous and asynchronous counters using JK-flipflop.
• Shift Registers: For data storage and manipulation, serial-to-parallel or parallel-to-serial data conversion the shift registers are widely used. Registers can store and shift the binary data in a sequential manner. We can design it by JK-flipflops.
• Memory Units: JK-flipflop itself act as a memory unit to store binary information. By making a sequential chain of JK-flipflops we can use it even as RAM.

Advantages of JK Flip-Flop

• Versatility: As discussed above, JK-flipflops can be used as a basic memory element or a primary building block of further complex memory design. It is very much adaptive as it can be operated in both synchronous and asynchronous modes.
• Toggle Functionality: The application which are required to get output as its complement of input that also can be developed by JK-flipflops as when J=K=1 it triggers toggle state which gives output which is complement with it’s each clock pulse.
• Error Detection and Correction: We can use a complex circuit built by JK-flipflops which can detect and correct information during data-transmission.

Disadvantages of JK Flip-Flop

• Complexity: Compared to other types of flipflops(D,T, SR), JK flipflop requires additional logic gates to implement which consumes extra memory resources and increases complexity to operate.
• Propagation Delay: This is the major problem present in JK-FF. Propagation delay results a timing delay in certain application which are time-flow sensitive.
• Race Problem: This issue arises when the clock input’s timing pulse isn’t given enough time to turn “Off” before the output Q’s state is altered.

Conclusions

The JK flip flop is a popular type of sequential logic circuit. It fixes some issues found in the SR flip flop. It stores binary information and also allows for toggling. It can work in both synchronous and asynchronous modes. Apart from that it can handle error detection, correction, and making counters.

Now, there are some challenges with the flip-flop—things like propagation delay and race conditions. But these can be managed with a Master-Slave setup.

Frequently Asked Questions on JK Flip-Flop – FAQ’s

What is toggle in JK flip flop?

Toggle in JK flip flop is a condition in which the output of flip flop changes to its opposite state and this change is occurs with each clock pulse. If the current output is 1, it will change to 0 and if the current output is 0, It will change to 1, this occurs then when both the inputs of flip-flop J = 1, K = 1.The flip-flop toggles/changes its state on each clock cycle, which makes it useful for counters or frequency dividers.

What is the difference between JK Flip Flop and SR Flip Flop?

Both JK flip flop and SR flip flop are used to store binary information and control the output state. The differences is in their Input configuration, Invalid state, Toggling, Applications, etc.

What is master slave JK flip flop?

Master slave flip flop is a combination of 2 JK flip-flops connected together in series. In this one flip flop acts as Master and the other flip flop acts as Slave. This configuration eliminate the problem timing and race conditions that occurs in basic JK flip flop.