PROPERTIES OF DIGITAL DEVICES
PART I: Voltage Transfer Characteristics
Normally the voltage inputs to a logic gate should be either “high” or “low”, (resulting in either “low” or
“high” outputs), and we try to avoid anything in between. But how high must the voltage be to be
counted as “high”, and how low to be counted as “low”? To answer this type of Voltage Threshold
question we will sweep the voltage input into an inverter from 0 to 5V (ie from min to max and
everything in between) and observe how the output responds.
Pre-Lab Part I
i) Read / review the material about voltage thresholds, noise margins, and voltage transfer characteristics
ii) Obtain the data sheets for the 74LS04 and the CMOS 4069 hex inverter chips
iii) Using the pin out given in the 74LS04 data sheet, draw the circuit you intend to build in the lab:
 The function generator is used to drive the input to one (of the six) inverters on the chip
 Tie the inputs of the remaining / unused gates together, and connect them to Ground.
 Make sure you show the 5V and 0V power connections
 Make sure all pin numbers are shown on your diagram
iv) For each device draw up, and complete as far as possible a table such as that outlined below, leaving
the “measured” column blank, for completion during the lab. The final noise margin will be the
smallest value obtained. Provide all calculations! If you do this in Word, (which will integrate well
with the results obtained into Word during the Lab), you must bring a printout with you to class.
Parameter
Low level Voltage Input, VIL
High level Voltage Input, VIH
Low level Voltage Output, VOL
High level Voltage Output, VOH
Hence calculated Noise Margin
Min
Typical
-
Max
Measured Units
-
Lab Procedure
i) Set up the function generator to output a 0 to 5V sawtooth waveform at 1kHz:
 Always set up the function generator before connecting it to your circuit, since the function
generator’s default output on power-up could damage your circuit components.
 While setting up your function generator, monitor its output on the oscilloscope (use AutoScale),
so that you can see whether it is behaving as you expect. Then on the function generator…
 Select a Sawtooth waveform:
 Push the Ampl button, hit the green Enter Number, and enter 2.5 Vpp according to the green
labels adjacent to each key. This gives a 5V amplitude waveform, oscillating about zero volts.
 Push the Offset button, hit the green Enter Number, and enter 1.25 Enter in order to raise the
waveform by 2.5 volts.
 You should now have the desired waveform. Check it on the oscilloscope
ii) Set up the power supply to give 5V power out of the “6V”(max) terminals.
 Always set up the power supply before connecting it to your circuit.
 Push the +6V key to show which terminals you wish to adjust
 Switch the Output On in order to see the voltage presently being outputted at the terminals


Adjust this value to 5.0V using the rotary knob. You can increase or the sensitivity of knob using
the < or > keys.
Use the Output Off button (not the Power button!) to switch the output off before connecting to
your circuit, or whenever modifying your circuit.
iii) Build the circuit you designed in your pre-lab
 Pin 1 of the chip is identified by the notch in the top of the chip
 Color-code your wires: use red for 5V power, black for 0V Ground, and white for signals
 Make your wires as short as possible; long loopy wires quickly get tangled and make it hard to
see what goes where.
 Connect the ground of the function generator to that of the power supply, so that all signals share
the same ground reference.
 Toggle the power supply Output On.
iv) Capture a plot showing how the output voltage of the inverter gate responds to the input voltage,
(which is not a nice “low” or “high” signal, but is sweeping from 0 to 5V).
 Connect Channel 1 of the oscilloscope to the inverter gate input driven by the function generator,
and Channel 2 to the inverter gate output. Use AutoScale to display the signals, then adjust
manually if necessary.
 Log onto the computer using your standard username and password, and either use the Benchlink
software (recommended) or the 3000 InterLink software to capture the scope’s screen.
 If Interlink is used, then this starts MS Word, with a special new toolbar which looks like this:


Click on the camera Snapshot icon on this toolbar to capture the oscilloscope display, and to
insert it into your document.
Annotate your plot with a title, and a label for each of the two waveforms, and explain briefly why
you might expect to see something similar to what you have obtained. Save your work!
v) Capture a plot showing the inverter gate’s Voltage Transfer Characteristic (VTC).
 Hit the Horiz button on the oscilloscope panel, press Time Mode in the Horizontal menu and
then, select “XY”. This plots Channel 2, (the output voltage), on the Y axis, against Channel 1,
(the input voltage), on the X axis. Maximize the size of the plot by manually adjusting each
channel’s position (using the small knob), and scaling (using the large volts/division knob).
 Capture and insert a Snapshot of the display you obtain into your Word document, and again add
appropriate title and labeling.
 Using Word’s drawing capability, you can add lines / arrows / textboxes to your plot, showing the
points at which the gradient = -1, and hence what values of VIL, VOH, and VIH, VOL, you obtain for
this inverter. As well as indicating graphically how you obtain these values from the plot, add
them to the tables you prepared in your pre-lab work.
vi) Repeat this entire experiment with the CMOS 4069 Hex inverter.
 The CMOS and LS-TTL devices are pin compatible, so all you need do is toggle the power supply
Output Off, carefully lever out the LS7404 chip, (don’t try to pull it out with your fingers as
one end always comes out first, and the pins at the other end are then damaged), and insert the
CMOS 4069 device in its place.
vii) Write comments on your results, eg measured versus data sheet values, LS-TTL versus CMOS
PART II: Power Supply Current and Power Dissipation
Pre-Lab Part II
i) Read the lab procedure and review your notes on power supply current and power dissipation
ii) For the LS device, prepare the following tables. Some entries you may be able to obtain or calculate
from the data sheets
Parameter
Quiescent IC supply current, outputs high, ICCH
Quiescent IC supply current, outputs low, ICCL
Average quiescent IC supply current, ICC
Average quiescent supply current per gate, (ICC / 6)
Average quiescent power dissipation per gate
Typical
Max
Measured
Units
Measured Supply Current when switching at different Frequencies, with 47pF Capacitive Load
Parameter
1 kHz
10 kHz
100 kHz
1 MHz
Units
Average IC supply current, ICC
Average supply current per gate, (ICC / 6)
Average power dissipation per gate
Estimated power dissipation per gate (pre-lab)
iii) For the CMOS 4069 Hex inverter device, prepare the following tables. Some entries you may be able
to obtain or calculate from the data sheets
Parameter
Quiescent IC supply current, outputs high, IDDH
Quiescent IC supply current, outputs low, IDDL
Average quiescent IC supply current IDD
Average quiescent supply current per gate, (IDD/6)
Average quiescent power dissipation per gate
Typical


Max


Measured
Units
Measured Supply Current when switching at different Frequencies, with 47pF Capacitive Load
Parameter
1 kHz
10 kHz
100 kHz
1 MHz
Units
Average IC supply current, IDD
Average supply current per gate, (IDD / 6)
Average power dissipation per gate
Estimated power dissipation per gate (pre-lab)
iv) Using the pin out given in the data sheet, draw the circuit you intend to build in the lab
Lab Procedure
i) Insert the multimeter in series with the 5V power supply line, so that the current from the 5V terminal
of the power supply flows through the meter to the Vcc of the chip.
 Do not connect the multimeter across the 0 and 5V supply lines. This will blow the
multimeter’s fuse if you try to measure the resulting (short circuit!) current.
 Make sure the red lead from the multimeter is plugged into the multimeter’s current measurement
socket (labeled I in red)
 On the multimeter front panel, press the blue Shift key followed by DC I.
ii) First measure the d.c. / quiescent supply current
 Tie all inputs low ( all outputs will be high), measure and record the supply current in your table
 Tie all inputs high ( all outputs will be low), measure and record the supply current in your table
 Compute, and record in your table, the average supply current, and hence the average per gate
iii) Now measure the average supply current when the input is switching as a 50% duty cycle square
wave, and when the output has a capacitive load.
 Add capacitive loading to each inverter, by adding a 47pF capacitor between the gate output of
each inverter and ground.
 Tie all the inputs together, so that they may all be driven from the same source.
 Apply a 0-5V square wave to this common input. If you’ve already had the function generator
set up for the 0-5V sawtooth, all you need do is press the
button, (otherwise set up for 0-5V
operation as described in Part I, procedure i)
 Record in your table the power supply current at 1kHz, 10kHz, 100kHz, 1MHz. To change
frequency, (to 10kHz, for example), press the Freq key, then Enter Number and the value 10
followed by kHz . Note that since the waveform is square wave, you are getting an average of the
current when the output is low and when it is high.
iv) Compute the average current and power dissipation per gate, recording these in your table
v) Replace the 74LS04 chip with the CMOS 4096 hex inverter, and repeat parts i) to iv).
 You should notice that the quiescent supply current is not sensitive to the level being outputted.
This is why CMOS data sheets do not differentiate between output high and low quiescent currents
vi) For each chip, plot (using Matlab or otherwise) the power dissipated per gate against frequency, using
loglog scales. Plot both sets of results on the same graph.
vii) Write comments on your results in your notebook, eg measured versus data sheet values, LS-TTL
versus CMOS, capacitive load and the effect of frequency.
PART III: Average Propagation Delay Time, Power-Delay Product, and Energy Delay Product
Pre-Lab Part III
i) Read the lab procedure and review your notes on propagation delay, power delay product (PDP), and
energy delay product (EDP).
ii) Copy the following “ring oscillator” circuit into your notebook, and add pin numbers so that you
know exactly how to construct it prior to the lab.
iii) Sketch the type of waveform you might expect at the output of the circuit
iv) For each device draw up, and complete as far as possible a table such as that outlined below, leaving
the “measured” column blank, for completion during the lab. For the pre-lab, predict the PDP and
EDP values.
Parameter
Period of Oscillation
Average propagation delay per gate
Power dissipation per gate (@1MHz)
Power-delay product
Energy-delay product
Typ / Min

Max

Measured
Units
Lab Procedure
i) Using the 74LS04, and 47pF capacitors, build the circuit you designed
 Note the circuit is self oscillating, so no input is needed!
ii) Measure the period of your ring oscillator, and record it in your table
 Connect Channel 1 of the oscilloscope to ring oscillator output. Use AutoScale to display the
signals, then adjust manually if necessary.
 Select Quick Measure on the oscilloscope front panel, then press Freq and then Period on the
buttons below the display. Record the period.
iii) Capture a snapshot of the ring oscillator output, and insert it into your Word document, [see part I iv)]
iv) Complete your table of results by calculating the propagation time delay for a single gate, and then
(using your results from part II), the time-delay product for the gate
v) Repeat, using the CMOS 4096 inverter chip
vi) Comment on your results in your notebook.