# lab3 - State University of New York at Stony Brook...

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State University of New York at Stony Brook Department of Electrical and Computer Engineering ESE 218 Digital Systems Design Spring 2009 Lab 3. Two-level implementations 1. Objectives De sign of 2-to-1 data selectors implementing SOP and POS algebraic expressions. A naly sis of the circuits for possibility and specifics of glitches. Glitch-free design. 2. Introduction Designing combinational circuits we have to ensure that the circuit operates properly for all possible input combinations. Some combinations can be hazardous causing unwanted glitches that appear at the output due to different propagation delays on different paths though the circuit. Glitch is an unexpected short-time change in the output value. The concept of glitch-free design will be illustrated on the example of data selectors or multiplexers widely used in digital systems. The circuit you are going to design allows propagation of signal from input A to output F with control signal C =1 and propagation of signal B to the output with C = 0. One of the possible implementations is shown in Figure 1. Figure 1. 3. Prelab 1. Obtain the algebraic expression for output F for the circuit in Figure 1 in the sum- of-products (SOP) form. Draw the circuit diagram for NAND–NAND implementation of the expression. Assuming the same propagation delay of 10 ns for all gates, obtain the timing diagram for output F when the data inputs are both at logical 1 level and the control input value changes from 0 to 1 then, after 50 ns, A B C F Control input Data inputs F2 F1

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2 changes back from 1 to 0. To do that first draw the timing diagrams for
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lab3 - State University of New York at Stony Brook...

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