TTL, ECL, TOTEM POLE CONCEPTS

1. Logic Family
By
AJAL.A.J ( A.P- ECE)- FISAT
ec2reach@gmail.com , Mob : 8907305642
1

2. Logic Family Definition
• A circuit configuration or approach used to
produce a type of digital integrated circuit.
• Consequence: different logic functions, when
fabricated in the form of an IC with the same
approach, or in other words belonging to the
same logic family, will have identical electrical
characteristics.
• the set of digital ICs belonging to the same logic
family are electrically compatible with each other
2

3. 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.

4. Common Characteristics of
the Same Logic Family
• Supply voltage range, speed of response,
power dissipation, input and output logic
levels, current sourcing and sinking capability,
fan-out, noise margin, etc.
• Consequence: choosing digital ICs from the
same logic family guarantees that these ICs are
compatible with respect to each other and that
the system as a whole performs the intended
logic function.
4

5. 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)

6. DIODE TRANSISTOR LOGIC
DIODE TRANSISTOR LOGIC
5V FILL IN THE TRUTH TABLE
+V
A A Y
DIODE
1k 0 0
0V
A 0 1
Y
1k
MMBT3904
1 0
DIODE 1 1
0V
B
What logic function is this circuit?

7. RTL Example
7

8. Basic Logic Families
• TTL – transistor-transistor logic
based on bipolar transistors.
• CMOS – complementary metal-oxide
semiconductor logic based on metal-
oxide-semiconductor field effect
transistors (MOSFETs).
• ECL – emitter coupled logic based on
bipolar transistors.

9. Basic Logic Families
TTL CMOS ECL

10. General Characteristics of
Basic Logic Families
• CMOS consumes very little power,
has excellent noise immunity, and is
used with a wide range of voltages.
• TTL can drive more current and uses
more power than CMOS.
• ECL is fast, with poor noise
immunity and high power
consumption.

11. Introduction
• Uses bipolar technology including
NPN transistors, diodes and
resistors.
• The NAND gate is the basic building
block
• Contains different subfamilies with
varying characteristics such as
speed and power consumption
11

12. Example Logic Families
• General comparison or three commonly
available logic families.
the most important to understand

13. Standard TTL NAND Gate
13

14. What is a totem pole?
In art and history….
Totem poles are carved and
painted vertical logs, constructed
by many northwest coast native
American Indian people. The poles
display mythological images,
animal spirits whose significance is
their association with the lineage.
14

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

16. Totem pole in TTL ?
• What is totem pole?
– addition of an active pull up circuit in the
output of a gate is called totem pole. Using
Q3 and Q4 to achieve this purpose
• Why totem pole?
– To increase the switching speed of the
gate which is limited due to the parasitic
capacitance at the output.
16

17. Totem Pole Outputs
• The standard TTL output
configuration with a HIGH output and
a LOW output transistor, only one of
which is active at any time.
• A phase splitter transistor controls
which transistor is active.

18. Totem Pole Outputs

19. Advantages of Totem
Pole Configuration
• Changes state faster than open-
collector outputs.
• No external components are
required.

20. Totem Pole Switching
Noise
• Caused by one output transistor
turning off slower than the other
turns on.
• Briefly shorts VCC to ground.
• Prevented with use of decoupling
capacitors.

21. NOT Gate 7404
21

22. NOR Gate 7402
22

23. AND Gate 7408
23

24. OR Gate 7432
24

25. XOR Gate
25

26. Transistor-Transistor Logic
Families
• Transistor-Transistor Logic Families:
– 74L Low power
– 74H High speed
– 74S Schottky
– 74LS Low power Schottky
– 74AS Advanced Schottky
– 74ALS Advance Low power Schottky

27. Standard TTL Transistor Switching
Problem
• Trs are driven into deep saturation to fully
conduct, or cutoff to switch off.
• The result of deep saturation is that the two
junctions are now forward biased.
• The forward biasing of the BC junction
forces a large number of minority carriers
to the collector region.
• When the Tr switches off, these minority
carriers needs to be removed. This takes a
finite amount of time called the storage time
(major component of the propagation delay)
and thus increases the switch off time. 27

28. MOSFET Types
• Depletion-mode.
• Enhancement-mode:
– n-channel
– p-channel
• CMOS (complementary) constructed
from both n- and p-channel
transistors.

29. MOSFET Types

30. MOSFET
METAL OXIDE SEMICONDUCTOR
FIELD EFFECT TRANSISTORS
P-CHANNEL ENHANCEMENT N-CHANNEL ENHANCEMENT
TO TURN ON GATE MUST BE TO TURN ON GATE MUST BE
LOWER THAN SOURCE HIGHER THAN SOURCE

31. MOSFET
METAL OXIDE SEMICONDUCTOR
FIELD EFFECT TRANSISTORS
C-MOS
5V 5V 5V 5V 5V
+V +V +V +V +V
10k
S 10k
S P-MOS
5V 5V
D G P-MOSD G
0V Vin P-MOS 0V Vin
Vout
0V G N-MOS 0V G D N-MOS D
10k 10k N-MOS
S S
TO TURN ON TO TURN ON ON
TO TURN TO TURN ON
GATE HIGHER GATE HIGHER
GATE LOWER GATE LOWER
THAN SOURCE THAN SOURCE
THAN SOURCE THAN SOURCE

32. MOSFET BIAS
Requirements
• Operates in two modes:
• Cutoff – acts as a very high
impedance between the drain and
the source.
• Ohmic – equivalent of saturation.
Acts like a relatively low resistance
between the drain and the source.

33. CMOS
COMPLIMENTARY
METAL OXIDE SEMICONDUCTOR

34. CMOS
COMPLIMENTARY
METAL OXIDE SEMICONDUCTOR
C-MOS
5V
+V
P-MOS
0V Vin
Vout
N-MOS

35. CMOS Quiescent vs.
Dynamic Current
• Quiescent current flows when the
gate is in a steady state and is
usually small.
• Dynamic current flows when the gate
is changing state.
• The faster a CMOS gate switches, the
more current (and the more power) it

36. Power Dissipation
• The measure of energy used over
time by electronic logic gates.
• The product of the voltage and
current required for the operation of
the circuit.

37. Fan-In
• Number of input signals to a gate
– Not an electrical property
– Function of the manufacturing process
NAND gate with a
Fan-in of 8

38. Fanout Definitions
• Driving gate is the gate whose output
supplies current to the inputs of other
gates.
• Load gate is a gate whose input current is
supplied by the output of another gate.
• A measure of the ability of the output of
one gate to drive the input(s) of
subsequent gates

39. Fanout
• The number of gates that a logic gate
is capable of driving without
possible logic error.
• Limited by the maximum current a
gate can supply in a given logic state
versus the current requirements of
the load.

40. Fan out
• Also known as loading factor
• Defined as the maximum number of
logic inputs that an output can drive
reliably
• A logic circuit that specify to have 10
fan out can drive 10 logic inputs
©2009, CE Department

41. • How many 74LS00 NAND gate inputs
can be driven by a 74LS00 NAND gate
outputs ?
Solution:
Refer to data sheet of 74LS00, the maximum values of
IOH = 0.4mA, IOL = 8mA, IIH = 20uA, and IIL = 0.4mA
Hence,
fan-out(high) = IOH(max) / IIH (max)=0.4mA/20uA=20
fan-out(low) = IOL(max) / IIL(max)=8mA/0.4mA=20,
the overall fan-out = fan-out(high) or fan-out(low)
whichever is lower.
Hence, overall fan-out = 20

42. ECL

44. ECL
EMITTER COUPLED LOGIC

45. The ECL Digital IC Family
8-14 The ECL Digital IC Family
Basic ECL circuit – differential amplifier
This circuit produces complementary
outputs: VOUT1 , equal to VIN ,
and VOUT2 , equal to VIN.

46. The ECL Digital IC Family
8-14 The ECL Digital IC Family
ECL OR/NOR Gate
OR
The fundamental ECL gate.
The basic ECL circuit can be
used as an INVERTER if
the output is taken at VOUT1.

47. The ECL Digital IC Family
8-14 The ECL Digital IC Family
• ECL characteristics:
– Very fast switching with typical propagation delay
of 360 ps—faster than TTL or CMOS.
– The standard ECL logic levels are nominally
-0.8 V and 1.7 V for logical 1 and 0 respectively.
– Worst-case noise margins approximately 150 mV.
– ECL logic gates usually produce an output and its
complement, eliminating the need for inverters.
– Current flow remains constant, eliminating noise
spikes

49. PLD’S

50. PLD’sInputs
Most of these
devices are based on
a two level structure
(sum of products
form).
AND products
OR
plane plane
outputs

51. In practice this might be
represented as:
inputs PLD notation
A B C D
•The fusible
links are made A.C + B.C D + A
at the x’s,
otherwise outputs
blown.

52. Inverted inputs
A B
inputs
A.B + A.B A + B
= B
outputs

53. PLD’s
– The main types of PLD include:
• PLA’s (programmable logic arrays)
• PAL’s (programmable array logic)
• PROM’s (programmable read only
memory)

54. PLA’s
A B
A programmable logic array
(PLA) has all links
programmable in both AND and
OR arrays.
Very flexible.
Many applications don’t require
such flexibility

55. – AND plane PALs
programmable AABB
– OR plane
fixed A
F4 F1
– Not so flexible
1
– Operate faster B 3
P
because hard- 2
wired OR’s
F5 F8
switch quicker
than programmable links
programmed
links.

56. PAL’s AABB
• P = A.notB +
notA.B
A
• Use gate 1 to
F4 F1
implement the 1st
product term and 1
P
3
gate 2 to B
2
implement the
second F5 F8
• First term blow F2
and F3
• Second term blow
F5 and F8

57. PALs Shorthand Notation
A B CD E
P
P = A.C.D