Transcript integrated circuit

Magnitude Comparator
Dr. Ahmed Telba
Integrated Circuits
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An integrated circuit is a piece (also called
a chip) of silicon on which multiple gates or
transistors have been embedded
These silicon pieces are mounted on a plastic
or ceramic package with pins along the edges
that can be soldered onto circuit boards or
inserted into appropriate sockets
Integrated Circuits
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SSI, MSI, LSI: They perform small tasks such as addition of few
bits. small memories, small processors
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VLSI Tasks: - Large memory - Complex microprocessors, CPUs
An SSI chip contains
independent NAND gates
Examples of Combinational
Circuits
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a) Decoders
b) Encoders
c) Multiplexers
d) Demultiplexers
E) Magnitude Comparator
Decoder
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Accepts a value and decodes it
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Output corresponds to value of n inputs
Consists of:
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Inputs (n)
Outputs (2n , numbered from 0  2n - 1)
Selectors / Enable (active high or active low)
The truth table of 2-to-4
Decoder
2-to-4 Decoder
2-to-4 Decoder
The truth table of 3-to-8
Decoder
A2
A1
A0
D0
0
0
0
1
0
0
1
0
1
0
0
1
1
1
0
0
1
0
1
1
1
0
1
1
1
D1
D2
D3
D4
D5
D6
D7
1
1
1
1
1
1
1
3-to-8 Decoder
3-to-8 Decoder with Enable
2-to-4 Decoder: NAND
implementation
Decoder is enabled when E=0 and an output is active if
it is 0
2-4 Decoder with 2-input and
Enable
Decoder Expansion
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Decoder expansion
 Combine two or more small decoders with
enable inputs to form a larger decoder
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3-to-8-line decoder constructed from two
2-to-4-line decoders
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The MSB is connected to the enable inputs
if A2=0, upper is enabled; if A2=1, lower is
enabled.
Decoder Expansion
Combining two 2-4 decoders to form
one 3-8 decoder using enable switch
The highest bit is used for the enables
Combinational Circuit Design with
Decoders
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Combinational circuit implementation with
decoders
n
 A decoder provide 2 minterms of n input
variables
 Since any Boolean function can be
expressed as a sum of minterms, one can
use a decoder and external OR gates to
implement any combinational function.
Combinational Circuit Design with
Decoders
Example Realize F (X,Y,Z) = Σ (1, 4, 7) with a decoder:
1 bit Digital comparator
4-bit Magnitude Comparator
BCD to 7-Segment Display
Decoder
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BCD to 7-Segment Display Decoder
As we saw in the previous tutorial, a Digital Decoder IC, is a device which converts one digital format into another and one of
the most commonly used device for doing this is called the Binary Coded Decimal (BCD) to 7-Segment Display Decoder. 7segment LED (Light Emitting Diode) or LCD (Liquid Crystal Display) type displays, provide a very convenient way of displaying
information or digital data in the form of numbers, letters or even alpha-numerical characters.
Typically 7-segment displays consist of seven individual coloured LED’s (called the segments), within one single display package.
In order to produce the required numbers or HEX characters from 0 to 9 and A to F respectively, on the display the correct
combination of LED segments need to be illuminated and BCD to 7-segment Display Decoders such as the 74LS47 do just that.
A standard 7-segment LED display generally has 8 input connections, one for each LED segment and one that acts as a common
terminal or connection for all the internal display segments. Some single displays have also have an additional input pin to
display a decimal point in their lower right or left hand corner.
In electronics there are two important types of 7-segment LED digital display.
1. The Common Cathode Display (CCD) – In the common cathode display, all the cathode connections of the LED’s are joined
together to logic “0″ or ground. The individual segments are illuminated by application of a “HIGH”, logic “1″ signal to the
individual Anode terminals.
2. The Common Anode Display (CAD) – In the common anode display, all the anode connections of the LED’s are joined
together to logic “1″ and the individual segments are illuminated by connecting the individual Cathode terminals to a “LOW”,
logic “0″ signal.
BCD to 7-Segment Display
Decoder
74LS47 for common-anode LED
types
Truth Table for 7 Segment
display
4-to-2 Bit Binary Encoder
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Priority Encoder
The Priority Encoder solves the problems mentioned above by allocating a priority
level to each input.
The priority encoders output corresponds to the currently active input which has the
highest priority. So when an input with a higher priority is present, all other inputs
with a lower priority will be ignored.
The priority encoder comes in many different forms with an example of an 8-input
priority encoder along with its truth table shown below.
3-8 Binary Decoder with
Enable
2-to-4 Line NAND Binary Decoder Logic Diagram
De multiplexer
Magnitude comparator