1. EET 1131 Unit 9 Logic Families
Read Kleitz, Chapter 9.
Homework #9 and Lab #9 due next week.
Quiz next week.
-Collect HW 8, and do Quiz #8.
-Handouts: pages 5-7 of 7404/LS04/S04 datasheet; pages 2-3 of 74HC04 datasheet; practice sheets: ICTechnologies and threeKindsofOutputs.
-Also bring TTL Cookbook & CMOS Cookbook.

2. Two Main Goals of Unit 9
Make sense of the most important numbers in a datasheet.
Understand the three kinds of output pins that you’re likely to encounter:
Totem-pole outputs
Open-collector outputs
Three-state outputs

3. Two Kinds of Transistors
In Electronic Devices & Circuits (EET 2201) you’ll study two major classes of transistors:
Bipolar Junction Transistors (BJTs)
Metal-Oxide Semiconductor Field Effect Transistor (MOSFETs)

4. Logic Families Three major logic families:
TTL (Transistor-Transistor Logic) based on bipolar junction transistors
CMOS (Complementary Metal Oxide Semiconductor) based on MOSFETs
ECL (Emitter-Coupled Logic), based on bipolar junction transistors
Originally, TTL chips were fast but used lots of power, and CMOS chips used little power but were slow.
CMOS chips are sensitive to static discharge, and must be handled carefully.
-These families vary by speed, power consumption, cost, voltage & current levels…. 4

5. 7400 Series and 4000 Series
A popular series of TTL chips is the 7400 series that you’ve used in this course: Wikipedia's list
A popular series of CMOS chips is the 4000 series: Wikipedia's list
-Note that many in the 7400 list say “open-collector output” or “three-state output.”
-Pass around TTL Cookbook & CMOS Cookbook. 5

6. Some Subfamilies within the TTL Family
Description
Designator
Example
Standard TTL
None
7404
Low-Power Schottky LS
74LS04
Advanced Low-Power Schottky
ALS
74ALS04
Fast F
74F04
The 7404, the 74LS04, the 74ALS04, and the 74F04 all perform the same logic functions.
But they differ in terms of their performance characteristics (primarily speed and power consumption). 6

7. Some Subfamilies within the CMOS Family
Description
Designator
Example
Standard CMOS
4069
Pin-compatible with 7400 series C
74C04
High-Speed CMOS HC
74HC04
Advanced High-Speed CMOS
AHC
74AHC04
Low-Voltage CMOS (3.3 V)
LVC
74LVC04
Advanced Low-Voltage CMOS (2.5 V)
ALVC
74ALVC04 7

8. Review: Voltage and Current
A wire is like a water pipe. The amount of
electricity per second flowing through a wire is called
current, which is measured in amperes.
The voltage (pressure)
at this point
is greater than
the voltage
at this point.
A voltage source is like a water pump. Its voltage rating (in volts)
tells you how strong it is.
Power (measured in watts) is the rate at which energy is used. Power = Voltage  Current
Resistors are like partial blockages
in the pipe. They restrict the amount
of current that flows through the circuit.

9. Some Electrical Quantities and Units
Quantity
Symbol
Unit
Symbol for the Unit
Current I
ampere A
Voltage V
volt
Power P
watt W
Resistance R
ohm 
For example,
To say that a voltage is 5 volts, we write V = 5 V
To say that a current is 30 milliamperes, we write I = 30 mA

10. Basic Operational Characteristics and Parameters
Consult datasheets for
DC supply voltage
Input/output current and fan-out
Input/output voltages and noise margin
Propagation delay
Power dissipation
Speed-power product
Example datasheets:
7404 TTL inverter
74HC04 High-Speed CMOS inverter
A slide on each of these follows.

11. DC Supply Voltages
TTL chips are optimized for 5 V supply, and cannot tolerate voltages far above or below 5 V.
CMOS chips may be optimized for 5 V, 3.3 V, 2.5 V, or 1.8 V supplies. Most CMOS chips can tolerate a much wider range of supply voltages than TTL chips.
Check datasheets, & fill in practiceICTech.doc

12. Current-Sourcing and Current-Sinking
For TTL:
A HIGH output sources current
A LOW output sinks current.

13. Input and Output Currents
Four key current parameters:
IIH = the current flowing through an input pin when it’s HIGH.
IIL = the current flowing through an input pin when it’s LOW.
IOH = the current flowing through an output pin when it’s HIGH.
IOL = the current flowing through an output pin when it’s LOW.
In all cases, a negative sign on the current value means current is leaving the gate through the pin. No negative sign means current is entering.
Check datasheets, & fill in practiceICTech.doc

14. Fan-out
Fan-out means the number of load inputs that a given output can drive.
With TTL, current is the limiting factor in determining fan-out.
With CMOS, capacitance is the limiting factor.

15. Example: Calculating TTL Fan-out
For a standard TTL gate:
A LOW input sources up to 1.6 mA.
A LOW output can sink up to 16 mA.
Also:
A HIGH input sinks up to 40 A.
A HIGH output can source up to 400 A.
Thus, standard TTL has a fan-out of 10.
See Wisconsin Online’s Fan-out Lesson
Check datasheets & do calculations to fill in practiceICTech.doc

16. Logic Levels
Four key voltage parameters when you’re interfacing logic:
VIH(min) = the minimum voltage that an input pin will recognize as a HIGH.
VIL(max) = the maximum voltage an input pin will recognize as a LOW.
VOH(min) = the minimum voltage that can appear on an output pin when it’s HIGH .
VOL(max) = the maximum voltage that can appear on an output pin when it’s LOW.
Check datasheets, & fill in practiceICTech.doc

17. Logic levels for TTL

18. Noise Margin VNH = VOH(min) − VIH(min) VNL = VIL(max) − VOL(max)
The noise margin is the room for error between the voltage that an output pin produces and the voltage that an input pin expects.
VNH = VOH(min) − VIH(min)
VNL = VIL(max) − VOL(max)
Do calculations to fill in practiceICTech.doc

19. Propagation Delay
Data sheets specify propagation delays for low-to-high output transitions (tPLH) and high-to-low output transitions (tPHL).
A device with a smaller propagation delay can run faster (at a higher frequency) than a device with a higher propagation delay.
Next slide shows example waveforms.
Check datasheets, & fill in practiceICTech.doc

20. Figure 9.10 (Continued) (b) propagation delay times.

21. Power Dissipation
Recall that power equals current times voltage (P=IV).
So a chip’s power dissipation is given by its supply voltage (VCC) times its supply current (ICC). (Note that we don’t use the voltages and currents on input or output pins.)
A lower-power device wastes less energy, generates less heat, and costs less to run than a higher-power device.
Check datasheets, & fill in practiceICTech.doc

22. Speed-Power Product
A useful overall measure of a device’s performance is its speed-power product, found by multiplying its average power dissipation times its average propagation delay.
The lower the speed-power product, the better.
Do calculations to fill in practiceICTech.doc

23. Interfacing Logic Families
We’ve seen that different logic families have different voltage and current specifications.
These differences can cause problems when you connect a gate from one family to a gate from another family.

24. Voltage-Related Interfacing Problems
In some interfacing situations, a HIGH output pin may produce a voltage that is too low to be recognized as a HIGH by the input pin it’s connected to.
The solution in such cases is to use a pull-up resistor. See example on next slide.

25. Interfacing Example: TTL to CMOS
A TTL HIGH output may be as low as 2.4 V.
But a CMOS input expects HIGHs to be at least 3.33 V.
Solution: use a pull-up resistor, as shown in Figure 9-27.

26. Current-Related Interfacing Problems
In some interfacing situations, either a HIGH output pin may not source enough current to drive the input pin it’s connected to, or a LOW output pin may not sink enough current to drive the input pin it’s connected to.
The solution in such cases is to use a buffer. See example on next slide.

27. Interfacing Example: CMOS to TTL
A CMOS LOW output can only sink 0.51 mA.
But as much as 1.6 mA may flow out of a TTL LOW input.
Solution: use a CMOS buffer, as shown in Figure 9-29.

28. Two Main Goals of Unit 9
Make sense of the most important numbers in a datasheet.
Understand three kinds of output pins that you’re likely to encounter:
Totem-pole outputs
Open-collector outputs
Three-state outputs

29. Three Kinds of Outputs TTL chips can have three kinds of outputs:
Totem-pole (the most common)
Open-collector (discussed in Chapter 9)
Three-state (discussed in Chapter 13)

30. Totem-Pole Output
Most chips you’ve used up to now have had totem-pole outputs.

31. A standard TTL inverter circuit.
-Do practice sheet: threeKindsofOutputs
-In analog circuits, transistors typically behave as amplifiers. In digital circuits, they act as switches, either in cutoff or saturation.
-If input is LOW, Q1 on, Q2 off, Q3 off, Q4 on. If input is HIGH, Q1 off, Q2 on, Q3 on, Q4 off.

32. Open-Collector Output
Missing a transistor internally, so you must provide an external pull-up resistor.
Two advantages:
Allows for the use of higher-than-usual voltages and currents.
Allows a trick called “wired-AND,” which means you can AND the outputs of two chips by tying them directly together. (Never tie totem-pole outputs together.)

33. TTL inverter with open-collector output.
Advantage is higher current-carrying capacity.

34. Open-collector symbol in an inverter.

35. Some Open-Collector Chips
7405 (Hex Inverters with Open-Collector Outputs)
7409 (Quad 2-Input AND with Open-Collector Outputs)
7412 (Triple 3-Input NAND with Open-Collector Outputs)
Others: 7422, 7433 35

36. Three-State Output (also called tri-state output)
In addition to the two usual output states (HIGH and LOW), has a third output state called high-impedance (“high-Z”).
In the high-Z state, the output is disconnected from the external circuit.
Useful when the outputs of many chips are tied to the same bus: at any time, only one of them should be connected to the bus.

37. The three states of a tristate circuit.

38. Basic tristate inverter circuit.

39. Some Three-State Chips
74251 (Data Selectors/Multiplexers with 3-State Outputs)
74LS348 (8-Line To 3-Line Priority Encoders With 3-State Outputs) 39

40. A CMOS inverter circuit.
-2 transistors, a p-channel MOSFET (Q1) and an n-channel MOSFET (Q2).
-When input is LOW, Q1 is on and Q2 is off.
-When input is HIGH, Q1 is off and Q2 is on.

41. Three Kinds of CMOS Outputs
Like TTL chips, CMOS chips can have two kinds of special-purpose outputs instead of the usual outputs:
Open-drain
Similar to open-collector in TTL
Requires an external pull-up resistor
Three-state

42. Other Logic Families
TTL and CMOS are by far the two most common logic families, but you may also encounter chips from other families:
ECL (Emitter-Coupled Logic): The fastest logic family
PMOS (p-Channel Metal Oxide Semiconductor)
NMOS (n-Channel Metal Oxide Semiconductor)
E2CMOS (Electrically Erasable CMOS)