Digital Techniques Diploma (Poly) 3rd semester

 



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Alternate Logic-Gate Representations

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Alternate Logic-Gate Representations We have discussed the five basic logic gates (AND, OR, INVERTER, NAND, and NOR) and the standard symbols used to represent them in a logic circuit diagram. Most of the logic networks use standard symbols. But in some networks an alternative set of symbols is used in addition to the standard symbols. The table shows the alternate set of symbols for the five basic gates. Table: Alternate Logic Gate Representations To convert any normal symbol to its corresponding alternate symbol, the following steps are used: METHODOLOGY: TO CONVERT STANDARD SYMBOL TO ALTERNATE SYMBOL Step 1: Add bubbles (indication of inversion) at those input or output points where it is not present. Step 2: Remove all pre-existing bubbles of the normal symbol, if there is any at the point (only NOT, NAND and NOR gates) Step 3: If the existing normal logic symbol is AND, change it to OR, Similarly, if it is OR, then change it to AND. There is no change for the triangular symbol of ...
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Introduction of K-Map (Karnaugh Map) Part 2

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  5 variable K-Map in Digital Logic Karnaugh Map  or K-Map is an alternative way to write truth table and is used for the simplification of Boolean Expressions. So far we are familiar with 3 variable K-Map & 4 variable K-Map. Now, let us discuss the 5-variable K-Map in detail. Any Boolean Expression or Function comprising of 5 variables can be solved using the 5 variable K-Map. Such a 5 variable K-Map must contain   = 32 cells . Let the 5-variable Boolean function be represented as : f ( P Q R S T)  where P, Q, R, S, T are the variables and P is the most significant bit variable and T is the least significant bit variable. The structure of such a K-Map for SOP expression is given below : The cell no. written corresponding to each cell can be understood from the example described here: Here for variable  P=0, we have Q = 0, R = 1, S = 1, T = 1 i.e. (PQRST)=(00111)  . In decimal form, this is equivalent to  7 . So, for the cell shown above the c...
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An Introduction to Digital Logic Families

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  What is a Logic Family? In Digital Designs, our primary aim is to create an Integrated Circuit (IC). A Circuit configuration or arrangement of the circuit elements in a special manner will result in a particular Logic Family. What are the advantages of creating different Logic Families? Electrical Characteristics of the  IC will be identical. In other words, the different parameters like Noise Margin, Fan In, Fan Out etc will be identical. Different ICs belonging to the same logic families will be compatible with each other. Some Characteristics we consider for the selection of a particular Logic Family are: Supply voltage range  Speed of response  Power dissipation  Input and output logic levels  Current sourcing and sinking capability Fan-out  Noise margin The basic Classification of the Logic Families are as follows: Bipolar Devices MOS Devices Hybrid Devices  Bipolar Families: Diode Logic (DL) Resistor Transistor Logic (RTL) Diode Transistor...
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