2. Logic families
Ic technology changes from time to time.
The technology depends on following
factors
Speed
Power dissipation
Noise immunity
Input/output interface compatibility
Cost
3. Desirable qualities
High speed
Low power dissipation
High noise immunity
Single output to be obtained from many
i/p.
Compatibility : connecting the output of
one device to input of other.
Interfacing: design of interconnection
between circuits that shift the voltage
levels and current levels to make them
compatible.
4. Classification of digital Ic families
Digital IC classified as
Bipolar families MOSFET families
Resistor transistor logic(RTL) PMOS Pchannel
Diode transistor logic(DTL) NMOS Nchannel
Transistor transistor logic (TTL) Complementary MOS
Emitter coupled logic (ECL)
5. TTL
TTL is most popular of ssi and msi.
TTl Uses diodes and transistors for basic
NAND gates this technology is called DTL
Diodes were replaced by transistor to improve
the circuit operation and this logic family was
called TTL.
Built from bipolar junction transistors and
resistors .
It is called TTL because both logic gating
function and amplifying function is performed
by transistors.
6. TTL APPLICATIONS
Most widely used logic family
In computers
Industrial controls
Test equipment's
Consumer electronics
Military and aerospace.
Ttl is an ex of SSI & LSI
7. Variation in ttl
Standard ttl
High speed ttl
Low power
Schotty
low powerSchottky
Advanced Schottky
Low voltage ttlSchottky
8. ECL
Also called as current mode logic
Obtained through bipolar transistor that compute logical
functions.
CHARACTERISTICS/ advantages
Change state rapidly thus operate at high speed.
Fastest of logic family since propagation time is less
than nano seconds.
Does not depend on state of the circuit.
Little power noise is generated.
9. Disadvantage ,Usage-Ecl
Transistor draw current continuously
Circuit requires more power and wastage is more.
Power requirements:
TTl- 5 volts
Ecl – (-5.2v)negative power supplies.
USAGE
When high performance is required, high speed
application.
Older version of Main frame computers.
Super computers and signal processors.
11. MOS
Unipolar transistor depends on only one
type of carrier.
Carrier may be electrons or holes.
Used in Lsi & vlsi
Metal electrode is placed on top of oxide
insulator ie the semiconductor material.
Mosfet is used where power consumption
is low.
12. PMOS,NMOS,CMOS
P channel mos is referred as pmos.
P oldest and slowest obsolete.
Nmos n channel and used in circuits with one
type of MOS transistor.
Nmos used in microprocessor and memories.
CMOS combination n and p channel.
Cmos is also explained as “Complementary –
Symmetry”.
Cmos uses Symmetrical pairs of electronic
devices p type and n type.
13. Characteristics of Cmos
High input resistance.
Compatible output of one device can be
connected to another CMOS.
High noise immunity
Low static power
High density on chip
Simple
Protection circuitry
Absorb electric charges with no damage.
14. Usage Cmos
Microcontrollers, microprocessor, RAM
Image sensors, data converter and integrated
transceivers and other types of communication.
Current IBM mainframes .
Digital wristwatches, calculators and portable
computers.
ADVANTAGE
Dissipate less power .
Operates on high speed.
Low cost
More economical operation
15. Disadvantage
Power consumption increases with clock speed.
Higher noise
COMPARISONS TTL,ECL,CMOS
Ttl Ecl Cmos
Power
consumption
increase with
clock speed
Power
consumption is
high
Power consumption
does not increase
Less sensitive
elecrostatic
discharge
More sensitive
electrostatic discharge
Nand gate Nor gate Not gate
