Lab Exercise 8: Signal Propagation Delays
CSCE 231: Digital Systems
Name(s): __________________
Assigned: Thursday, Apr. 10, 2014; Due: Thursday, Apr. 17, 2014 by 5:25PM __________________
Work individually or in a group of two students
1
Demonstrations
Breadboard and oscilloscope measurement for inverter schematic
Points
/30
TA Initials Date
Objectives:
1.
Observe signal delays and the timing hazards that can arise in digital systems
2.
Revisit breadboarding, using a DC power supply, using a DMM, and working with an IC
3.
Learn how to use a function generator and an oscilloscope
Directions: Do the pre-lab reading first (if needed) before proceeding to the lab tasks.
Pre-Lab Tasks:

Read the Function Generator and Oscilloscope tutorials on the course website if you are unfamiliar or rusty with this lab equipment

Read Module 8 from the Digilent Real Digital website if you need more details about signal propagation delays
Lab Tasks: There are two parts to this lab exercise (breadboard and simulation) which may be done in either order. Morken 212 must be used for breadboarding. If you are familiar with the use of the
Function Generator and Oscilloscope, I recommend you do the breadboarding first. If you are unfamiliar with this lab equipment, I recommend you do the breadboarding last.
Breadboard: (please refer to the DC power supply, DMM, Function Generator, and Oscilloscope tutorials on the course website)
You will need:

A station with a DC power supply, DMM, function generator, and an oscilloscope

A breadboard and a number of wires

One 7404 IC

Four connectors (to connect to the DC power supply and DMM)

Three probes (one to connect the function generator to the breadboard, two to connect the oscilloscope to the breadboard)
1.
You will use one integrated circuit (IC) in this lab; a 7404 (INV) chip. The pinout is shown below:
F
1
A F
2

2.
Breadboard the schematic shown next to the pinout. What is the relationship between A and F
1
?
Between A and F
2
? Explain this relationship in discussion question 1.
a.
If you are not sure if you have wired your design correctly, ask the instructor or lab assistant to help you verify your design. Remember, incorrect wiring or voltages may destroy ICs or damage laboratory equipment. b.
Use 4 V for V
CC
and 0 V for ground (GND). Note, these are different voltages than what we used in lab 1. Remember to connect the DC power supply to your IC. c.
Use the DMM to verify the logic value between each inverter; this will verify that the IC is functioning correctly. Ask the instructor or lab assistant to take a look if you observe an unexpected value. d.
Power down your circuit and connect the function generator and oscilloscope to your circuit i.
Function Generator’s Probe
1.
The red alligator clip of the probe should be connected to A, and the black clip should be connected to ground (this probe will set the input) ii.
Oscilloscope’s Two Probes
1.
The red alligator clip of one probe should be connected to A, and it’s black clip should be connected to ground (this probe will allow you to view the input)
2.
The red alligator clip of the second probe should be connected to F
1
, and it’s black clip should be connected to ground (this probe will allow you to view the output) iii.
Ask the instructor or lab assistant to help you verify that you have properly connected the function generator and oscilloscope.
3.
Turn the function generator on and produce a square wave with a: a.
Frequency of FREQ = 1 MHz (note, this is different than the function generator tutorial) b.
Amplitude of VhiZ = +4.00 Vpp c.
DC offset of DC = +2 V d.
Duty cycle or symmetry of SYM = 50% e.
This will create a square wave from 0 V to 4 V with a frequency of 1 MHz; it is 4 V half of the time and 0 V half of the time
4.
Turn on the DC power supply and oscilloscope, and output the signal from the function generator
5.
Measure the propagation delay from input A to output F
1
using the oscilloscope a.
Remember, propagation delay is measured from the time at 50% of A (about 2 V in our case) to the time at 50% of F
1
(also about 2V in our case) b.
Write down this propagation delay for discussion question 2
6.
What is the propagation delay from input A to output F
2
? a.
Estimate and explain your estimation of this delay for discussion question 3 b.
Measure the propagation delay from input A to output F
2
using the oscilloscope c.
Write down this propagation delay for discussion question 4 d.
Show the instructor or lab assistant your oscilloscope measurement before you turn off or disconnect equipment. This is demonstration 1.
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Simulation:
Complete Problems 1 through 4 of Project 8 from the Digilent Real Digital website. Use VHDL to design the circuits. Print out the pages for these questions and write the answers to the questions. Follow the directions and also print waveforms and VHDL models of circuits when asked. Submit this for discussion question 6.
Discussion (70 pts): Type and print your answers to these questions on a separate sheet of paper
1.
What is the relationship between A and F
1
? Between A and F
2
?
2.
What is the measured propagation delay from A to F
1
?
3.
What do you estimate for the propagation delay from A to F
2
? Please explain your estimation.
4.
What is the measured propagation delay from A to F
2
?
5.
What is the percent error between your estimation and the measured value for questions 3 and 4?
Use (T estimated
– T measured
)/T estimated
* 100% to calculate by how much percent your estimate was larger
6.
Include your answers for problems 1-4 from project 8 (the simulation lab task)
(or smaller) than the measured propagation delay. Why do you believe your estimate was incorrect? Please explain your reasoning.
7.
Look at Problem 5 of Project 8 from the Digilent Real Digital website. Estimate the answers to the questions for this problem without simulating the circuit. Please explain your reasoning.
8.
List the references you used for this lab assignment (e.g. sources/websites used or students with whom you discussed this assignment)
3