EGR220 Than & Gab Lab #7

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Introduction and Objectives

TTL (Transistor Transistor Logic) are fundamental

components of digital electronics. Therefore, to

understand their characteristic is really important.[1].

Therefore, in this lab, we were instructed to measure

and analyze the characteristic of TTL devices. The

primary objectives of this lab are:

1. To analyze and understand the nature of

terminal characteristic of TTL

2. To understand the propagation delay

3. To understand the transfer function of TTL

Equipments and Components used

In this lab, the equipments and components we used

are:- TTL two-input quad NAND gate SN7400 (x3)

Hex-inverter 7404 (x1)1KΩ Potentiometer, 10KΩ

Potentiometer, a breadboard, a waveform generator,

±20V power supply, a multi-meter, wires and cords.

Procedures

Procedure 1: Analyzing the Terminal

Characteristic of TTL

Gate

Under

Test

Input Output

+5V

1k

Figure 1.

We built the circuit in figure 1. We applied an

input voltage equal to the maximum of the low level

voltage specified by the manufacturer (0.8V), and then

adjusted the output current of the gate under test to be

equal to the maximum low level output current (IOL)

specified by the manufacturer (4mA). The resistance

was calculated by V/I = 200Ω.

Then, we measured VIH and IIH at the gate under test,

and compared to the manufacturer's data. We got VIH

for 3.8V, which was greater than min VIH ind data

sheet, which is 2V. For IIH, we got 10μA which was

less than max IIH (20μA). We expected that these

parameters would change with a change in output

current. Then, we measured VOL, and we got VOL =

0.16V, which was a little bit less than typical VOL

(0.25V)

Gate

Under

Test

Input Output

10k

Figure 2.

We connected the circuit in figure 2. We applied

an input voltage equal to the minimum of the high

level voltage specified by the manufacturer (2V), and

then adjusted the output current of the gate under test

to be equal to the minimum high level output current

(IOH) specified by the manufacturer (0.4mA). The

resistance was calculated by V/I = 5KΩ.

hen, we measured VIL and IIL at the gate under test,

and compared to the manufacturer's data. We got VIL

for 0.7V, which was less than max VIL ind data sheet,

which is 0.8V. For IIL, we got 1.04mA which was less

than max IIL (1.6mA). We expected that these

parameters would change with a change in output

current. Then, we measured VOH, and we got VOH =

1.8V, which was close to min of VOH (2.4V)

Then, we calculated NH = IOH/ IIH and NL = IOL /

IIL; NH = 40 and NL = 3.8.

Procedure 2: Analyzing Propagation Delay of TTL

tPHL is the high to low propagation delay and tPLH is the

low to high propagation delay.

EGR220 Than & Gab Lab #7

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We connected 8 TTL gates in series and the input

square wave was provided. Then, the output square

wave was connected to oscilloscope and compared

with the input square wave.

Total tPHL = 50ns. Therefore, 50/8 =6.25 ns for each

gate. Typical tPHL = 7ns. Therefore, the measurement

was close enough.

Total tPLH = 100ns. Therefore, 100/8 =12.5 ns for each

gate. Typical tPLH = 11ns. We concluded that the

measurement was close enough.

Procedure 3: Analyzing Transfer Function of TTL

We used the 7404 Hexinverter IC and varied the input

voltage VIN from 0 to 5V in 1.0V increments. And we

used a Multimeter to measure and record the output

voltage, and plotted the input voltage vs. output

voltage.

When Vin = 0, Vout = VOH. Therefore, VOH = 3.3V.

Again, we found that VOL = 0.35V. Between 1V and

2V, there should be some values which has a slope = -

1. After examining, VIL ≈ 0.9V and VIH ≈ 1.8V. When

compared these values to data sheet, we found that the

measured data was close enough.

Discussion

In order to understand 3 characteristic of TTL

gates, we analyzed terminal characteristic,

propagation delay and transfer function. Although

the measurement are close enough to the values

described in data sheet, there are many factors

which can affect the measurement, such as

temperature, the equipments and measurement

methods.

References [1] Sedra, Adel S., and Smith. Kenneth C. “Microelectronics

Circuits”. 5th. New York: Oxford University Press, 2004.

0 1 2 3 4 5 6

0

0.5

1

1.5

2

2.5

3

3.5

Vout