Types of Flip-Flops in Digital Electronics
Flip-Flops in Digital Electronics:
Flip-flop is a binary cell capable of storing one bit of information. It has two outputs, one for the normal value and one for the complement value of the bit stored in it. A flip-flop maintains a binary state until directed by a clock pulse to switch states. The difference among various types of flip-flops is in the number of inputs they possess and in the manner in which the inputs affect the binary state.
Types of Flip-Flops:
The most common 4 types of flip-flops presented below:
SR Flip-Flop has three inputs, labelled S (for set), R (for reset), and C (for clock). It has an output Q and sometimes the flip-flop has a complemented output. It is indicated with a small circle at the other output terminal. There is an arrowhead-shaped symbol in front of the letter C to designate a dynamic input. The dynamic indicator symbol denotes the fact that the flip-flop responds to a positive transition (from 0 to 1) of the input clock signal.
The D (data) flip-flop is a slight modification of the SR flip-flop. An SR flip-flop is converted to a D flip-flop by inserting an inverter between S and R and assigning the symbol D to the single input. The D input is sampled during the occurrence of a clock transition from 0 to 1. If D = 1, the output of the flip-flop goes to the 1 state, but if D = 0, the output of the flip-flop goes to the 0 state.
A JK flip-flop is a refinement of the SR flip-flop in that the indeterminate condition of the SR type is defined in the JK type. Inputs J and K behave like inputs S and R to set and clear the flip-flop, respectively. When inputs J and K are both equal to 1, a clock transition switches the outputs of the flip-flop to their complement state.
T flip-flop is obtained from a JK type when inputs J and K are connected to provide a single input designated by T. The T flip-flop has only two conditions. When T = 0 (J = K = 0) a clock transition does not change the state of the flip-flop.
When T = 1 (J = K = 1) a clock transition complements the state of the flip-flop. These conditions can be expressed by a characteristic equation:
The most common type of flip-flop used to synchronize the state change during a clock pulse transition is the edge-triggered flip-flop. In this type of flip-flop, output transitions occur at a specific level of the clock pulse. When the pulse input level exceeds this threshold level, the inputs are locked out so that the flip-flop is unresponsive to further changes in inputs until the clock pulse returns to 0 and another pulse occurs.
Some edge-triggered flip-flops cause a transition on the rising edge of the clock signal (positive-edge transition). Others cause a transition on the falling edge (negative-edge transition).
Another type of flip-flop used in some systems is the master-slave flip-flop. This type of circuit consists of two flip-flops. The first is the master, which responds to the positive level of the clock. The second is the slave, which responds to the negative level of the clock. The result is that the output changes during the 1-to-0 transition of the clock signal. The trend is away from the use of master-slave flip-flops and toward edge-triggered flip-flops.