In this lecture, we are going to learn about the Triggering Methods in Flip Flops. we will see how many types of triggering methods we use in sequential circuits like flip flop.
Triggering Methods in Flip Flops
In the latches and flip-flops, we use the additional signal for the controlling of the circuits called the clock signal.
Depending on which portion of the clock signal the latch or flip-flop responds to, we can classify the circuits into two types.
Types of Triggering Methods in Flip Flops
The types of Triggering Methods in Flip Flops are:
|Types of Triggering Methods in Flip Flops|
|1.||Level Triggered Circuit|
|2.||Edge Triggered Circuit|
Now we will discuss each type in detail.
Concept of Level Triggering
The latch or flip-flop circuits respond to their inputs, only if their enable input (E) to be held at an active HIGH or LOW level area called Level Triggered latches or flip-flops.
Figure (a) shows the symbol of a level-triggered SR flip-slop and figure (b) shows the clock signal applied at its input.
Types of Level-Triggered Flip-Flops
There are two types of level-triggered flip-flops:
- Positive level triggered
- Negative level triggered
Positive Level Triggered
- If the output of the S-R flip-flop responds to the input changes, for its clock input at a HIGH (1), level then it is called the positive level triggered S-R flip-flop.
- The circuit shown in the above figure (a) is a positive level triggered S-R flip-flop.
Negative Level Triggered
- If the outputs of an S-R flip-flop respond to the input changes, for its clock input at the LOW (0) level, it is called the negative level triggered S-R flip-flop.
Note: The level triggering is not used in practical circuits due to some of its disadvtanges.
Concept of Edge Triggering
The flip-flops that change their outputs only correspond to the positive or negative edge of the clock inputs area called edge-triggered flip flops.
These flip flops are therefore said to be edge-sensitive or edge-triggered rather than being level triggered.
The rectangular signal applied to the clock input of a flip-flop is shown in the above figure. If the same signal is applied as the clock signal to the flip flop, then its outputs will change only at the rising (positive) edge or at the falling (negative) edge of the clock.
Types of Edge-Triggered Flip-Flops
There are two types of edge-triggered flip-flops:
- Positive edge triggered flip flops
- Positive edge-triggered flip flops will allow its output to change only at the instants corresponding to the rising edge of the clock (or positive spikes). Its outputs will not respond to changes in input at any other instant of time.
- Negative edge triggered flip flops
- Negative edge-triggered flip flops will respond only to the negative going edges ( or spikes) of the clock.
Frequently Asked Questions
What is a triggered flip-flop?
A Flip Flop tends to change its state at either a positive edge (rising edge) or negative edge (falling edge) of the clock applied.
What are the two methods of edge triggering?
positive edge triggering and negative edge triggering.
What is triggering in digital techniques?
Triggering in Digital Electronics is the process of applying an external signal to induce a transition from one state to another.
What is the negative triggering in flip-flops?
A flip-flop becomes active when the clock signal goes from high to low and ignores the low-to-high transition
What is edge and level triggering?
In edge triggering, an event occurs at the rising edge or falling edge whereas, in level triggering, an event occurs during the high voltage level or low voltage level