What is meant by 'edge triggered'? Differentiate SR-FF and JK-FF with their functional operation and excitation tables.

Introduction

In digital circuits, the term 'edge triggered' refers to the behavior of certain types of sequential circuits, where changes in the output occur not just based on the current inputs, but also on the way the inputs change. This is particularly important in sequential circuits such as flip-flops and counters, where the timing of changes in input can significantly affect the output.

Detailed Explanation of Edge Triggering

Edge triggering in digital circuits is a type of triggering that allows the output of a circuit to change only at the onset of a pulse. There are two types of edge triggering: positive edge triggering and negative edge triggering.

Positive edge triggering allows the output to change at the onset of a pulse, i.e., when the pulse changes from a low voltage level to a high voltage level. This is represented by the formula:

If CLK(t-1) = 0 and CLK(t) = 1, then Q(t) = D(t)

Negative edge triggering, on the other hand, allows the output to change at the end of a pulse, i.e., when the pulse changes from a high voltage level to a low voltage level. This is represented by the formula:

If CLK(t-1) = 1 and CLK(t) = 0, then Q(t) = D(t)

SR-FF (Set-Reset Flip-Flop)

The Set-Reset Flip-Flop, or SR-FF, is a type of flip-flop that has two stable states, set and reset. It is controlled by two inputs, S and R, and has two outputs, Q and Q'. The operation of the SR-FF can be represented by the following formulas:

If S = 1 and R = 0, then Q = 1 and Q' = 0 (Set state) If S = 0 and R = 1, then Q = 0 and Q' = 1 (Reset state) If S = 0 and R = 0, then Q and Q' remain unchanged (Hold state) If S = 1 and R = 1, then Q and Q' are undefined (Invalid state)

The excitation table of the SR-FF is as follows:

JK-FF (JK Flip-Flop)

The JK Flip-Flop, or JK-FF, is a type of flip-flop that also has two stable states. It is controlled by two inputs, J and K, and has two outputs, Q and Q'. The operation of the JK-FF can be represented by the following formulas:

If J = 0 and K = 0, then Q(t+1) = Q(t) (Hold state) If J = 0 and K = 1, then Q(t+1) = 0 (Reset state) If J = 1 and K = 0, then Q(t+1) = 1 (Set state) If J = 1 and K = 1, then Q(t+1) = Q'(t) (Toggle state)

The excitation table of the JK-FF is as follows:

Comparison between SR-FF and JK-FF

The main differences between SR-FF and JK-FF in terms of their functional operation and excitation tables are as follows:

Conclusion

Understanding the concept of 'edge triggering' and the differences between SR-FF and JK-FF is crucial in the study of digital circuits and systems. These concepts form the basis for the design and operation of many digital systems, including counters, registers, and memory units.

Summary

Edge triggering refers to the behavior of certain types of sequential circuits, where changes in the output occur not just based on the current inputs, but also on the way the inputs change. There are two types of edge triggering: positive edge triggering and negative edge triggering. SR-FF (Set-Reset Flip-Flop) and JK-FF (JK Flip-Flop) are two types of flip-flops that have different functional operations and excitation tables.

Analogy

Edge triggering is like a traffic light changing from red to green only when the button is pressed. Similarly, in edge-triggered circuits, the output changes only when there is a specific change in the input signal.