ECEN 1521L
Basic Digital and Computer Circuits Laboratory
Experiment 2
Switching Circuits
NAME
PARTNER
1. Introduction to Switching Circuits. The instructor will present some background information
about voltage-controlled switches and a simple switching circuit called a NOT-gate. Listen
carefully and take some notes. Based on what you learn, complete the following:

An alternate name for a NOT-gate is an __________________

If a NOT-gate has an output named B and an input named A, then B is the _____________
or ____________ of A (two different words).

If a NOT-gate has an input named A and an output named B, then write the Boolean
equation for B in terms of A using the notation from the text: _______________
2. In real algebra (i.e., the algebra of real numbers), two inverses cancel. For example,
1/ (1/x) = x. Describe this in words.
In “switching algebra”, a similar
result holds. Complete the logicvalue truth table for the logic circuit
shown here, and then complete the
following equation:
(A′)′ = _______ .
3. Redraw the schematic above in #2, but connect one more inverter to C with its output named D.
Draw a new truth table which includes D, and fill in its values. Describe one or two possible
reasons for connecting inverters in series like this.
4. An electrical switching circuit called a NAND-gate is shown below in switching circuit form,
along with a partially-completed voltage-level truth table. Copy the table onto your lab report
and finish it by
filling in the
blanks. Then
construct a logicvalue (0’s and
1’s) truth table
using positive
logic.
5. Remember that a
low voltage at the
control terminal
closes a p-type
switch and opens
ECEN 1521L Exp 2 29-Jul-2017 04:28 AM (save date)
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an n-type switch, while a high voltage does the opposite. Based on the table entries given
above, does the bubble on the switches represent p-type or n-type switches? Explain your
thinking.
6. Read about the AND operation in your text (Roth 7th ed. p.38) and compare its truth table to the
one you just constructed. Why do you think this gate is called a “NAND” gate? (Hint: NAND
is a contraction of NOT and AND.)
7. Repeat step 4 for the gate shown at the right. Read
about the OR operation on p. 39, 7th ed. What is the
name of this gate?
This step should result in two tables, one like that
above showing switching operations, and the second
one being a logic-value truth table.
REPORT: Keep a complete record of all your data, results, observations, and answers to questions,
written neatly and legibly on the unlined side of standard engineering paper.
Attach these lab sheets as your cover pages. This is due by the end of the lab period!
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