University College of Science

MLSUCLASS- BCA 1st SEMESTER

TOPIC – logicAL FAMILIES

PRESENTED BY:- VAISHALI MANDOWARA

UNDER GUIDENCE OF:- Sonu Upadhyay Mam

Logic Family• Logic Families indicate the type of logic circuit

used in the IC.

• A Circuit configuration or arrangement of the circuit elements in a special manner will result in a particular Logic Family.

• The set of digital ICs belonging to the same logic family are electrically compatible with each other

Characteristics of Logic Families

The main characteristics of Logic families include:• Speed• Fan-in• Fan-out• Noise Immunity• Power Dissipation

Speed: Speed of a logic circuit is determined by the time between the application of input and change in the output of the circuit.

Fan-in: It determines the number of inputs the logic gate can handle.

Fan-out: Determines the number of circuits that a gate can drive.

Noise Immunity: Maximum noise that a circuit can withstand without affecting the output.

Power: When a circuit switches from one state to the other, power dissipates.

basic Classification of Logic Families are as follows:

• Bipolar Devices• Metal Oxide Semiconductor

Devices• Hybrid Device

Bipolar families• Bipolar transistors are fabricated on a chip in

digital integrated circuits.

• Bipolar technology is preferred for SSI [ Small scale integration ] and MSI [ Medium scale integration ] because it is faster.

Types of Bipolar Families:• Diode Logic (DL)• Resistor Transistor Logic (RTL)• Diode Transistor Logic (DTL)• Transistor- Transistor Logic (TTL)• Emitter Coupled Logic (ECL) or Current Mode

Logic (CML)• Integrated Injection Logic (IIL)

Diode Logic • In DL (diode logic), only Diode and Resistors

are used for implementing a particular Logic. Remember that the Diode conducts only when it is Forward Biased.

Disadvantages of Diode Logic• Diode Logic suffers from voltage degradation

from one stage to the next.

• Diode Logic only permits OR and AND functions

Resistor Transistor Logic In RTL (resistor transistor logic), all the logic are implemented

using resistors and transistors. One basic thing about the transistor (NPN), is that HIGH at input causes output to be LOW (i.e. like a inverter). In the case of PNP transistor, the LOW at input causes output to be HIGH.

Advantage:• Less number of Transistors

Disadvantage: • High Power Dissipation• Low Fan In

Diode Transistor Logic• In DTL (Diode transistor logic), all the logic is

implemented using diodes and transistors.

Disadvantage: •Propagation Delay is Larger

Transistor transistor logic• The first transistor–transistor logic family of integrated circuits

was introduced by Sylvania as Sylvania Universal High–Level Logic (SUHL) in 1963. Texas Instruments introduced 7400 Series TTL family in 1964. Transistor–transistor logic uses bipolar transistors to form its integrated circuits.TTL has changed significantly over the years, with newer versions replacing the older types.

• Since the transistors of a standard TTL gate are saturated switches, minority carrier storage time in each junction limits the switching speed of the device. Variations on the basic TTL design are intended to reduce these effects and improve speed, power consumption, or both.

Transistor Transistor Logic

Emitter Coupled Logic• ECL is the fastest of all logic families and

therefore is employed in applications where very high speed is essential .

• High speeds have become possible in ECL because transistors are used in differential amplifier configuration , in which the are never driven into saturation and thereby the storage delay time is eliminated.

Emitter Coupled Logic

Drawbacks of Emitter Coupled Logic:

• Low noise margins• High power dissipation.• It uses negative voltage supply which makes it

difficult to use ECL in conjunction with TTL and MOS circuits.

Integrated Injection Logic:• The integrated injection logic (IIL or I2L) uses

bipolar transistors in a kind of current-steering arrangement to form its integrated circuits. IIL is slightly easier to construct on an integrated circuit, and so was popular for early VLSI circuits.

MOS Families• MOS stands for Metal Oxide Semiconductor.• In these MOSFETs (Metal oxide semiconductor

field-effect transistor) are fabricated on chip.• It is used in LSI [Large scale integration] field

because more MOSFETs can be packed into the same chip area.

Types of MOS Families:• P-MOS Family• N-MOS Family• C-MOS Family

PMOS• PMOS stands for P-channel MOSFETs.• It is the oldest and slowest type of technology.• PMOS is the first high density MOS circuit

technology to be produced• It makes the use of enhancement mode P-

channel MOSFET transistors in forming the basic gate building blocks.

• There are no resistors in this circuits.

NMOS• N-MOS stands for N-channel MOSFETs.• N-MOS devices were developed as processing

technology improved.• N-MOS devices are most common because N-

channel processing is easier than P-channel processing.

• The N-MOS are widely used in microproccessors and microcircuits.

CMOS• CMOS stands for complementary MOSFETs.• CMOS devices are chips in which both P-

channel and N-channel enhancement MOSFETs are connected in a push-pull arrangement.

• CMOS are simple , small in size ,cheaper in fabrication and consume very little power.

Hybrid Family:• Bi-CMOS Family

BICMOS• One major improvement was to combine CMOS inputs

and TTL drivers to form of a new type of logic devices called Bi-CMOS logic.

• In the 1990s,modern integrated circuit fabrication technologies began to make Bi-CMOS a reality.

• This technology rapidly found application in amplifiers and analog power management circuits, and has some advantages in digital logic.

• Bi-CMOS circuits use the characteristics of each type of transistor most appropriately.

Highlights• RTL and DTL families have become obsolete

because of their low speed , high power dissipation , and low fan-out.

• TTL is the most popular general purpose logic family. It is available in different series with a wide range of operating speed, power dissipation and fan-out.

• ECL is the fastest logic family. For interfacing other logic families level-shifting networks are required.

•IIL is the only saturated bipolar logic family suitable for LSI because of small silicon chip area requirement and low power consumption . Because of low voltage requirement , it is highly suitable for battery operated systems.

•MOS devices occupy a very small fraction of silicon chip area as compared to bipolar devices and need very small power.

•The main disadvantage of MOS logic family is low speed , which is being improved upon by improvements in technology of MOS fabrications.

•IIL has the highest packing density and is mainly suitable for VLSI and ULSI.

•CMOS has slow speed but very small physical size and simple geometry . Its power dissipation is very small. It is widely used in electronic wrist watches, calculators, portable computers etc.

Thank

you