Sunday, March 04, 2012

Importance Of Buffers To Electronics

The buffer gate does not have a dot (bubble)
 because the bubble means invert which is a property
 of invertor gates, not buffer gates.
The Magical Buffer
Buffers take 1 input, A, and output 1 output B. The logic state of the output is a copy of the logic state of the input. As an equation, its function looks like this A = B. If you think that is pointless, then you are right! However; the buffer has a greater purpose that is less obvious than the average logic gate. From now on, think of a buffer gate as a refresher. A buffer refreshes the electric current of input A by its own active supply of power (logic high) and ground (logic low).

Image from All About Circuits (  
Practical Use and Application
Now, you know that buffers are used to refresh logic signals of high or low, but when would it be important to refresh logic signals? Let's say you have an AND gate (74xx08) that takes inputs, A and B, and outputs, AB, that needs to be used to create function X = ABC + ABD +ABE + ABF. There are 5 inputs, A, B, C, D, E, F, and one 1 output X which is dependent on the logic states of the 6 inputs (A,B,C,D,E,F). The output of the simple AB could be connected to 4 OR gate (74xx32) inputs because if any input, C,D,E,F are logic high along with the output of AB being high, then the final output of the function, X, would be logic high. In theory AB output could be sent to 4 individual OR gates without any change in the logic value AB, but sadly, the world is not perfect. Some of the electrical current, which is analog by nature (always changing), is lost in the 4  OR connections. Buffers would filter each of the 4 connections (outputs of AB) to strengthen the logic state. Over distance and processes, current is lost which can fall into the category of logic low. We do not want to lose our idealistic logic states. Better safe than sorry!

So, anytime you connect multiple logic inputs to the same output a buffer gate can ensure that each signal is in the logic high or low state by the time it reaches the several inputs. 

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