MULTISIM CHAPTER 3: MULTISIM 3.1 INTRODUCTION TO MULTISIM Multisim is a virtual electronic circuit design, analysis, and simulation programme that design and analyse analogue, digital and mixed mode circuits on a PC using virtual instruments. Virtual instruments are used to measure circuit behaviour such as voltage, current, power, frequency and signals on a scope. They look just like real instruments without fear of damaging the circuit components or the instruments. The basic virtual instruments in Multisim are: a) Multimeter It measures resistance, ac/dc voltage and ac/dc current. b) Function Generator It produces sinewave, squarewave and triangular wave signals of adjustable frequencies and amplitudes. c) Wattmeter It measures the power in watts consumed in a circuit. d) Oscilloscopes (2-ch and 4-ch). They display the traces of a peak-to-peak voltage signal in a circuit. e) Bode Plotter It produces a graph of the circuit’s frequency response. It is useful for analysing electronic filter circuits. f) Frequency Counter
34
Embed
razorjr.files.wordpress.com file · Web viewOther virtual instruments in Multisim include a Word Generator, a Logic Analyzer, a Logic Converter, an IV Analyzer, a Distortion Analyzer,
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
MULTISIM
CHAPTER 3: MULTISIM3.1 INTRODUCTION TO MULTISIMMultisim is a virtual electronic circuit design, analysis, and simulation programme that
design and analyse analogue, digital and mixed mode circuits on a PC using virtual
instruments. Virtual instruments are used to measure circuit behaviour such as voltage,
current, power, frequency and signals on a scope. They look just like real instruments
without fear of damaging the circuit components or the instruments.
The basic virtual instruments in Multisim are:
a) Multimeter
It measures resistance, ac/dc voltage and ac/dc current.
b) Function Generator
It produces sinewave, squarewave and triangular wave signals of adjustable
frequencies and amplitudes.
c) Wattmeter
It measures the power in watts consumed in a circuit.
d) Oscilloscopes (2-ch and 4-ch).
They display the traces of a peak-to-peak voltage signal in a circuit.
e) Bode Plotter
It produces a graph of the circuit’s frequency response. It is useful for
analysing electronic filter circuits.
f) Frequency Counter
It measures the frequency of an ac voltage signal.
Other virtual instruments in Multisim include a Word Generator, a Logic Analyzer,
a Logic Converter, an IV Analyzer, a Distortion Analyzer, a Spectrum Analyzer, a
Network Analyzer, a virtual Agilent Function Generator, Multimeter, and
Oscilloscope.
Types of electronic components that are available to build circuits in Multisim are:
a) DC and AC power sources, single phase and three phase
For a 2-input OR gate, output Y is HIGH if either input A or B is HIGH, or if both A and B
are HIGH; Y is LOW if both A and B are LOW.
Symbols:
Truth Table: INPUT (A) INPUT (B) OUTPUT (Y)
0 0 00 1 11 0 11 1 1
3.6.4 The NAND gateOperation:
For a 2-input NAND gate, output Y is LOW if input A and B are HIGH; Y is HIGH if either
A or B are LOW, or if both A and B are LOW.
Symbols:
AB
Y
AB
Y
AB
Y
Truth Table: INPUT (A) INPUT (B) OUTPUT (Y)
0 0 10 1 11 0 11 1 0
3.6.5 The NOR GateOperation:
For a 2-input NOR gate, output Y is LOW if either input A or B is HIGH, or if both A and
B are HIGH; Y is HIGH if both A and B are LOW.
Symbols:
Truth Table:INPUT (A) INPUT (B) OUTPUT (Y)
0 0 10 1 01 0 01 1 0
3.6.6 The XOR GateOperation:
For an exclusive-OR gate, output Y is HIGH if input A is LOW and input B is HIGH, or if
input A is HIGH and input B is LOW; Y is LOW if A and B are both HIGH or both LOW.
Symbols:
Truth Table: INPUT (A) INPUT (B) OUTPUT (Y)
0 0 00 1 11 0 11 1 0
3.6.7 The XNOR GateOperation:
AB
Y
AB
Y
For an exclusive-NOR gate, output Y is LOW if input A is LOW and input B is HIGH, or if
input A is HIGH and input B is LOW; Y is HIGH if A and B are both HIGH or both LOW.
Symbols:
Truth Table: INPUT (A) INPUT (B) OUTPUT (Y)
0 0 10 1 01 0 01 1 1
3.7 Basic Combinational Logic Circuits3.7.1AND-OR LogicFor a 4-input AND-OR logic circuit, the output X is high (1) if both input A and B are high (1), or
both input C and D are high (1).
3.7.2 AND-OR-Invert Logic
AB
Y
For a 4-input AND-OR-Invert logic circuit, the output X is LOW (0) if both input A and
input B are HIGH (1) or both input C and input D are HIGH (1)
3.7.3 Exclusive-OR Logic
3.7.4 Exclusive-NOR Logic
3.8 Functions of Combinational Logic
3.8.1 Multiplexer
A multiplexer is a device that allows digital information from several sources to be
routed onto a single line for transmission over that line to a common destination.
The basic multiplexer has several data-input lines and a single output lines.
Below is the logic symbol for a 4-input multiplexer (MUX). There are two data-
select lines because with two select bits, any one of four data-input lines can be
selected.
A 2-bit code on the data-select (S) input will allow the data on the selected data
input to pass through to the data output as table below:Data-select Inputs
Input selectedS1 S0
0 0 D0
0 1 D1
1 0 D2
1 1 D3
The data output is equal to the state of the selected data input
The total expression for the data output is
Y = D0S1’S0’ + D1S1’S0 + D2S1S0’ + D3S1S0
This can be implemented by the circuit below:
Because the data can be selected from any one of the input lines, this circuit is
also referred to as a data selector The select bits of multiplexer depend on the data input, 2n.
3.8.2 Demultiplexer
The DEMUX is a reverse multiplexer function.
It takes digital information from one line and distributes it to a given number of
output lines.
It is known as data distributors.
Below is the 1-line-to-4-line demultiplexer circuit.
The data input line goes to all of the AND gates.
The two data-select lines enable only one gate at a time and the data appearing
on the data-input online will pass through the selected gate to the associated
data-output line
3.8.3 Decoder
A decoder is a logic circuit that accepts a set of inputs that represents a binary
number and activates only the output that corresponds to that input number.
An AND gate can be used as a basic decoding element because it produces a
HIGH output only when all inputs are HIGH.
As example, to decode a binary number, 1001, make sure that all the inputs to
the AND gate are HIGH:
If a NAND gate is used in place of AND gate, a LOW output will indicate the
presence of the proper binary code
Below is the diagram of a general decoder with N inputs and M outputs:
N inputs M outputs
2N input codes only one output is high for eachinput code
Since each of the N inputs can be either 0 or 1, there are 2N possible input
combinations or codes. For each of these input combinations only one of the M
outputs will be active (HIGH); all other outputs are LOW.
In order to decode all possible combinations of 4-bits, 16 decoding gates are
required (24 = 16). This type of decoder is called a 4-line-to-16-line decoder
(because there 4 inputs and 16 outputs) or a 1-of-16-decoder (because for any
given code on the inputs, one of the 16 is activated).
An AND gate can be used to produce active-HIGH outputs and NAND gate to
produce active-LOW output.
Below is the logic symbol for a 4-line-to16-line decoder with active-LOW output.
The BIN/DEC label indicates that a binary input makes the corresponding
decimal output active. The input labels 8,4,2,1 represent the binary weights of the
input bits.
Decoder
Some decoders have one or more ENABLE inputs that are used to control the
operation of the decoder. With the ENABLE line held HIGH, the decoder will
function normally. With ENABLE held LOW, all the outputs will be forced to the
LOW state regardless of the levels at the inputs. Thus, the decoder is enabled
only if ENABLE is HIGH.
3.8.3.1 BCD –to- Decimal Decoder
The BCD-to-decimal decoder converts each BCD code into one of the 10
position decimal digit indications.
This decoder also is preferred as a 4-line-to-10-line decoder or a 1-of-10-line
decoder.
Only 10 decoding gates are required because the BCD code represent only 10
decimal digits, 0-9.
For input combinations that are invalid BCD, none of the output will be activated.
The BCD-to-7-Segment Decoder- accepts the BCD code on its input and
provides outputs to drive-7-segment display devices to produce a decimal
readout.
3.8.4 Encoder
An encoder accepts an active level on one of its inputs representing a digit, such as
decimal or octal digit, and converts it to a coded output, such as BCD or binary
The process of converting from familiar symbols or numbers to a coded format is
called encoding.
3.8.4.1 The Decimal-to-BCD Encoder
This type of encoder has 10 inputs- one for each decimal digit- and four output
Toggle Operation – When both inputs are HIGH, the output changes to the
opposite state on each successive clock spike (J=1, K=1, Q=1 and 0 repetitively).
A J-K flip-flop connected for toggle operation is sometimes called T flip-flop.
The functioning of J-K flip-flop is similar to S-R flip-flop except that J-K has no
invalid state.
Timing Diagram
LAB 3: COMBINATIONAL LOGIC CIRCUIT1.0 Objectives
At the end of this lab session, you should be able to:
explain the logic gates and combinational circuits.
construct combinational circuit in Multisim by using Logic Converter.
design a combinational circuit in Multisim.
2.0 Logic Tools in Multisim
Figure L3-1
One of the virtual instruments in Multisim is the Logic Converter. The arrow in the figure
L3-1 above shows the Logic Converter button.
Logic Converterbutton
Figure L3-2
When the Logic Converter button is clicked, the logic converter symbol is shown in the
figure L3-2 above.
Logic Converter
Figure L3-3
In the logic converter, most of the logic conversions needed is there. For example, if we
want to obtain a circuit for the following Boolean expression,
Firstly, enter the Boolean expression into the logic converter as below:
Then, click on the Boolean expression truth table conversions option:
Next, the Boolean expression can be simplified by clicking (Note that
for this example, the Boolean expression cannot be simplified anymore).
Finally, click to generate the combinational circuit which shown in figure
L3-4 below.
Truth table
Truth table conversion
Figure L3-4
3.0 Exercise
1. Construct a three-input combinational circuit for f = m (2, 4, 5, 7) with the aid of Multisim.
Show and explain all the steps in details.
2. Design a four-input combinational circuit for f = m (0, 2, 4, 6, 9, 12, 14) with the aid of
Multisim. Show and explain all the steps in details.
3. AB represents a two-bit binary number that can have any value (00, 01, 10, or 11); for
example, when A = 1 and B = 0, the binary number is 10, and so on. Similarly, CD
represents another two-bit binary number. Design a logic circuit, using A, B, C, and D inputs,
whose output will be HIGH whenever two binary numbers AB are equal and greater than CD. It is impossible for inputs AB and CD to be HIGH at the same time.
a) Draw the logic circuit from the simplified Boolean expression (use AND, OR and
NOT gates).
b) Draw the logic circuit from the simplified Boolean expression (use NAND gates).