Evolution of digital logic family

IN COMPUTER ENGINEERING, A LOGIC FAMILY MAY REFER TO ONE OF TWO RELATED CONCEPTS. A "LOGIC FAMILY" MAY ALSO REFER TO A SET OF TECHNIQUES USED TO IMPLEMENT LOGIC WITHIN VLSI INTEGRATED CIRCUITS SUCH AS CENTRAL PROCESSORS, MEMORIES, OR OTHER COMPLEX FUNCTIONS. THE MOST COMMON LOGIC FAMILY IN MODERN SEMICONDUCTOR DEVICES IS METAL–OXIDE–SEMICONDUCTOR (MOS) LOGIC, DUE TO LOW POWER CONSUMPTION, SMALL TRANSISTOR SIZES, AND HIGH TRANSISTOR DENSITY. 

1. Evolution of digital logic family

2. Presented By anik , Anirban saha 18-36207-1 Datta , bishowjit 18-37372-1 Rayhan , md. Abu masum 18-37219-1 Sharma, aninda kumar 17-35513-3

3. Introduction IN COMPUTER ENGINEERING, A LOGIC FAMILY MAY REFER TO ONE OF TWO RELATED CONCEPTS. A "LOGIC FAMILY" MAY ALSO REFER TO A SET OF TECHNIQUES USED TO IMPLEMENT LOGIC WITHIN VLSI INTEGRATED CIRCUITS SUCH AS CENTRAL PROCESSORS, MEMORIES, OR OTHER COMPLEX FUNCTIONS. THE MOST COMMON LOGIC FAMILY IN MODERN SEMICONDUCTOR DEVICES IS METAL–OXIDE–SEMICONDUCTOR (MOS) LOGIC, DUE TO LOW POWER CONSUMPTION, SMALL TRANSISTOR SIZES, AND HIGH TRANSISTOR DENSITY. 

4. Bipolar logic family(BJT) The Bipolar Junction Transistor is a semiconductor device which can be used for switching or amplification. Bipolar Junction Transistor BJT is two types: 1. Saturated 2. Non-saturated

5. Saturated

6. RTL (Resistor Transistor Logic) - In common use before the development of ICs.  - RTL circuits were first constructed with discrete components. Features - First logic family - Require minimum number of transistors.  Limitations Low speed, high power dissipation - Low fan out, poor noise immunity - Operating speed <4MHz

7. DTL (Diode-Transistor Logic) Use diodes and transistors. reduced power consumption faster than RTL Features First circuit configuration designed into IC. Very small in size and high reliability at very low price. Greater fan out and improved noise margins. Limitations - No low and constant output impedance in both states.

8. DCTL (Direct Coupled Transistor Logic) Direct coupled transistors. Base resistors of RTL are removed. Features Simpler than RTL, easy to fabricate. Fewer components hence economical. Limitations Small logic swing, poor noise margin. Current hogging.

9. IIL / I 2 L (Integrated Injection Logic) Merged Transistor Logic (MTL). Both PNP and NPN transistors are used. Designed around multi-collector inverting transistors. Features High component density, less power dissipation. Low metal interconnection. - Used in MSI and LSI designs. Limitations Poor noise immunity.

10. TTL (Transistor-Transistor Logic) Use all transistors totem pole output. Function of diodes in DTL is performed by multi-emitter transistor at input Features Fast switching time, larger fan out. Reduced silicon chip area. Easy to interface with other logic families. Limitations Large current spike when switching from low to high. Less noise immunity (0.4V)

11. HTL (High Threshold Logic) Logic Controllers with heavy noise Heavy Process Machinery Features Increased Noise Margin Spike Control High Noise Threshold Value Limitations Slow speed due to increased supply voltage resulting in use of high value resistors.  High power drawn

12. Non-Saturated

13. Schottky TTL A relatively fast bipolar logic family. Normally produced in integrated-circuit form. Limitations limited speed and frequency, noisy, very high power consumption at higher frequencies. Features It also has a relatively high switching In Schottky TTL the low cut-in voltage of the diode limits the base-collector voltage to about 400 mV, which prevents the transistor falling into saturation.

14. ECL (Emitter Coupled Logic) Non saturated logic/Current mode logic. Compliment output/eliminates the need of inverter. Features Fastest logic family Used in very high frequency applications. No noise spikes, large fan out. Limitations Require large silicon area, high power dissipation (high cost). Inconvenient voltage levels. - Low noise margins.

15. Unipolar logic family(FET)

16. 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.

17. 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 microprocessors and microcircuits.

18. 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.

19. Characteristics of Logic Families The main characteristics of Logic families include: - Fan-in - Fan-out - Power Dissipation ( p d ) - propagation delay ( t p ) - Noise Margin - speed-power product ( sPp )

20. FAN-IN:   The no of input of a gate that can be handled without impairing its normal operation is known as fan-in.  FAN-OUT: the maximum no of digital input of load that the output of single logic gate can feed or drive without impairing its normal operation is known as fan-out. POWER DISSIPATION:  power dissipation is the power consumed by the logic gates that must be available from the power supply. PROPAGATION DELAY: time taken for the output of a gate to change after the input is applied. NOISE MARGIN:  circuits ability to tolerate noise at the input side is known as noise immunity. SPEED-POWER PRODUCT:  it measures the performance of a logic circuits taking into account the t P AND P d . 

21. CONCLUSION Each logic family has unique electrical and electronics characteristic so they are unique and we can optimize them in circuit design by understanding their functionality and behavior.

22. Thank You