Latches in Sequential Logic Circuits

In this article, we will be discussing latches in deeper.

What are latches?

• The storage elements that are operated with signal levels rather than clock transitions are referred to as latches.
• It has two states – low and high and hence they are called bistable-multivibrators.
• They are level sensitive devices.
• Latches are the basic circuit of a flip flop.

Latches vs Flip Flops

Types of latches

SR Latch

SR latch is a circuit with two cross coupled NAND gates or two cross coupled NOR gates, and two inputs labeled S and R for set and reset respectively. The latch has two useful states – SET and RESET.

SET – When Q=1 and Q’=0

RESET – When Q=0 and Q’=1

Gated S-R Latch

A gated SR latch is a special type of SR latch, which has three inputs – Set, Reset and Enable. Set and reset inputs can be effective only when the enable input is active(when it is 1).

D Latch.

D latch has two inputs – Enable and Data. It is also known as transparent latch because the output is the same as the input passed to the data input when the enable is active (or it is 1).

Advantages of latches

• The latches consume less power.
• The designing of latches is very flexible when compared to flip flops.
• The latches are faster as they are not connected to clocks.
• The size and shape is very small and hence occupies very less space.

Aravind SS

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