Lab 2:
Diode Logic Design
Pengzhong Chen
Thai Le
15/09/2014
ENGR-307L: Semiconductor Electronics I
Introduction：
The aim of this lab is develop an understanding of using PN junction to design
practical digital gates. OR and AND logic gates will be constructed by
using PN junction diodes. Logic gates OR and AND both have two inputs.
For an AND logic gate, the truth table is presented in Table 1.
A
B
Output
0
0
0
0
1
0
1
0
0
1
1
1
Table 1
The truth table for OR gate is presented in Table 2.
A
B
Output
0
0
0
0
1
1
1
0
1
1
1
1
Table 2
As the Graph 1 shows, the current will be permitted when the anode is connecting
to the positive voltage and the cathode is connecting to the negative voltage. The current
will not be permitted when the anode is connecting to the negative voltage and the
cathode is connecting to the positive voltage. This is a very special property makes it
possible to construct practical logic gates with diodes.
Graph 1
The Graph 2 shows the structure for diode OR gate, and the Graph 3 shows the
structure for diode AND gate. All in all, the lab will be performed by building the OR
gate and AND gates with diodes and resistors based on graph 2 and graph 3.
Graph 2
Materials and Methods
Graph 3
The equipment and materials involved in this lab are list as follows:
Circuit Elements
Measuring Instruments and Power source
Physical Implementation
Computer simulation software
Two Silicon Diodes Resistor (1K ohms)
Digital Multimeter
Cadet Board
None
As we explained in the introduction part, the aim of this lab was to construct
practical logic gates using diodes. All the circuit diagrams that needed to be implement
on the Cadet board were presented in the introduction part. For the logic AND gate
implementation, two silicon diodes and a 1K resistor were needed. After placed the
circuits elements on the board, we connected the A and B port to the logic input on the
Cadet board as well as wiring the output from the circuit to the output indicator located
on the right side of the Cadet board. Then, we turned on the Cadet board and connect the
resistor to the power on the Cadet board, which is 5V. We tested all the four different
combinations of the inputs and record the results.
The second part of the lab was to build an OR gate with the silicon diode. The
similar approach was taken for this part. We follow the circuit presented in the
introduction part and used two diodes and one resistor, and the resistor was connected to
the ground. All the possible inputs were tested and we took all the pictures for all the
results. The pictures will be presented in the result part. Those will not only show the
inputs and outputs result, but also will also show how the circuits are implemented.
Results:
After building the circuit on the Cadet board, logic inputs buttons and logic output
indicator were being used to test the circuit. All the four possible combinations for logic
AND gate were implemented. All the logic inputs and outputs matched the table 1
presented on the Introduction part.
The Graph 4 is for both inputs low through the AND gate and the output indicator
indicates the result is low. The Graph 5 is for input A is high and input B is low, and the
output indicator indicates the result is low. The Graph 6 is input A is low and input B is
high, and the output indicator indicates the result is low. The Graph 7 is input A and input
B are both high, the output indicator indicates the result is high. These results match with
the truth table.
The same procedure was carried out for constructing OR gate. The Graph 8 is
input A and input B are both low, the output indicator indicates the result is low. The
Graph 9 is input A is high and input B is low, the output indicator indicates the result is
high. The Graph 10 is input B is high and input A is low, the output indicator indicates
the result is high. The Graph 11 is input A and B are high, the output indicator indicates
the result is high. These results match with the truth table.
.