Semiconductor Basics

11Logic Circuits

OBJECTIVES OF THIS CHAPTER

Now we are going back to talk about how we use semiconductor devices to perform useful operations. In the first two sections we'll talk about the way we interphase with the computer and the basic language we use, that is, Boolean algebra and logic symbols. Then I will explain how we implement this algebra with switches (to clear the concepts) and semiconductor devices, and we'll see how to do arithmetic operations, sums, subtractions, multiplications, and divisions with the devices we covered in the previous chapters.

In the previous chapters I very much concentrated on the performance of individual components and how to use them, mainly in the analogue mode. Now we are going digital.

11.1 Boolean Algebra

Everybody knows that digital computers work with 1s and 0s. Computers do not understand the number 3. All the computations that computers have to carry out to give us any meaningful results are done using the ON and OFF conditions, ON for 1 and OFF for 0. The large TV screen that give us beautiful and sharp pictures with bright colors is based on millions of points that can be ON or OFF. Each point of light consists of three miniscule LEDs of three different colors. How a computer manipulates all this data is based on the concepts of Boolean algebra. (Forget about the word algebra. There are no equations involved outside of adding and subtracting.)

Mr. George Boole (1815–1864; Figure 11.1) was a British mathematician and ...