Transistor Transistor Logic
- 4. Introduction Introduction to Digital logic gates Technologies Transistor Transistor Logic 7400 TTL Series TTL Sub-families Two Input TTL NAND Gate TTL Logic Levels and Noise Margins TTL Family Evolution Comparison to logic families
- 5. Introduction to Digital logic Gates ★ A Digital Logic Gate is an electronic device that makes logical decisions based on the different combinations of digital signals present on its inputs. ★ Digital logic gates may have more than one input but generally only have one digital output. ★ Individual logic gates can be connected together to form combinational or sequential circuits, or larger logic gate functions.
- 6. Technologies ★ The list of packaged building-block logic families can be divided into categories, listed here in roughly chronological order of introduction, along with their usual abbreviations: o Resistor–transistor logic (RTL) • Direct-coupled transistor logic (DCTL) • Resistor–capacitor–transistor logic (RCTL)
- 7. o Diode–transistor logic (DTL) Complemented transistor diode logic (CTDL) High-threshold logic (HTL) o Emitter-coupled logic (ECL) Positive emitter-coupled logic (PECL) Low-voltage positive emitter-coupled logic (LVPECL) o Transistor–transistor logic (TTL) o P-type metal–oxide–semiconductor logic (PMOS) o N-type metal–oxide–semiconductor logic (NMOS)
- 8. o Complementary metal–oxide–semiconductor logic (CMOS) o Bipolar complementary metal–oxide–semiconductor logic (BiCMOS) o Integrated injection logic (I2L)
- 9. Transistor - Transistor Logic ★ Transistor–transistor logic (TTL) is a class of digital circuits built from bipolar junction transistors (BJT) and resistors. ★ It is called transistor–transistor logic because both the logic gating function and the amplifying function are performed by transistors.
- 10. ★ The first transistor–transistor logic family of integrated circuits was introduced by Sylvania as Sylvania Universal High–Level Logic (SUHL) in 1963. ★ TTL manufacturers offered a wide range of logic gate, flip- flops, counters, and other circuits. Several variations of the original bipolar TTL concept were developed, yielding circuits with higher speed or lower power dissipation to allow optimization of a design.
- 11. ★ The design of the input and outputs of TTL gates allowed many elements to be interconnected. ★ Transistor-transistor logic (TTL) is a digital logic design in which bipolar transistor s act on direct-current pulses. ★ Many TTL logic gate s are typically fabricated onto a single integrated circuit (IC). ★ TTL ICs usually have four-digit numbers beginning with 74 or 54. ★ A TTL device employs transistors with multiple emitters in gates having more than one input.
- 12. 7400 TTL Series ★ TTL ICs first developed in 1965 and they are known as “standard TTL” . This version of TTL circuit is not available now. ★ TTL family use only transistor to perform the basic logic operations. ★ The standard TTL is improved to a great extent over the year. ★ TTL devices are still used as “glue” logic which connects more complex devices in digital system.
- 13. TTL Sub-families ★ There are several subfamilies or series of the TTL technology such as ★ Standard(74) ★ Low-power(74L), ★ High-speed(74H), ★ Schottky(74S), ★ Low-power Schottky(74LS), ★ Advanced Schottky (74AS), ★ Advanced low-power Schottky (74ALS).
- 14. Contd... ★ Commercial TTL ICs have a number designation that starts with 74 and follows with a suffix that identifies the series type. Examples are 7404, 74S86, and 74ALS161. ★ The speed-power product is an important parameter for comparing the various TTL series. ★ This is the product of the propagation delay and power dissipation and is measured in picojoules (pJ).
- 15. ★ The propagation delay of a transistor circuit that goes into saturation depends mostly on two factors: ○ storage time ○ RC time constants. ★ A pulse through a gate take certain amount of time from input to output. This interval of time is known as propagation time.
- 16. Two Input TTL NAND Gate
- 17. Standard TTL 74 Series ★ Offer a combination of speed and dissipation suited for many applications. ★ The 54 series is the counterpart of 74 series.
- 18. Low Power TTL, 74L series ★ Essentially the same basic circuit as the standard 74 series except that all resistance values (R1=40k R2=20k R3=12k R4=500) are increased. ★ Large resistance reduce the current and therefore, the power requirement,But at the expense of reduction in speed. ★ The power consumption of Low power TTL is about 1/10 of that of standard TTL.
- 19. High Speed TTL, 74H Series ★ Essentially the same basic circuit as the standard 74 series except that smaller resistance values (R1=2.8k R2=760 R3=470 R4=58) are used and the emitter follower transistor Q3 is replaced by Darlington pair and emitter to base joining of Darlington pair (Q5-Q3) is connected to ground through a resistor of 4k. ★ The switching speed of 74H series is approximately two times more than that of standard TTL.
- 20. Schottky TTL, 74S Series ★ A major slowdown factor in BJTs is due to transistors going in/out of saturation ★ Schottky diode has a lower forward bias (0.25V) ★ When BC junction would become forward biased, the Schottky diode bypasses the current preventing the transistor from going into saturation.
- 21. Low Power Schottky TTL, 74LS Series ★ Lower power and slower speed version of 74S series. ★ It uses the schottky clamped transistor, but with larger resistance values than those in the 74S series.
- 22. TTL Logic Levels and Noise Margins
- 23. TTL Series Name TTL Series Name Prefix Fan-Out Power (mw) dissipation Propagation Delay nSec Speed Power Product pJ Standard 74 10 10 9 90 Low-Power 74L 20 1 33 33 High-Speed 74H 10 22 6 132 Schottky 74S 10 19 3 57 Low Power Schottky 74LS 20 2 9.5 19 Advanced Schottky 74AS 40 10 1.5 15 Advanced Low Power Schottky 74ALS 20 1 4 4
- 27. Resistor Transistor logic ★ It has a fan-out of 5. ★ Propagation delay is 25ns. ★ Power dissipation is 12mw. ★ Noise margin for low signal input is 0.4v. ★ Poor noise immunity. ★ lLow speed.
- 28. Diode Transistor Logic ★ It has fan-out of 8. ★ It has high noise immunity. ★ Power dissipation is 12mw. ★ Propagation constant is average 30ns. ★ Noise margin is about 0.7v.
- 29. Emitter Coupled Logic ★ Propagation delay is very low (<1ns). ★ ECL is fastest logic family. ★ ECL circuit usually operate with -ive supplies (+ive terminal is connected to ground).
- 30. Transistor Transistor Logic ★ TTl has greater speed than DTL. ★ Less noise immunity. ★ Power dissipation is 10nw. ★ It has fan-in of 6 and fan- out of 10. ★ Propagation time delay is 5-15nsec.
- 31. CMOS ★ Dissipates low power, power dissipation is typically 10 nW per gate. ★ The propagation delays are usually around 25 nS to 50 nS. ★ Noise immunity approaches 50% or 45% of the full logic swing.
- 32. Online Sources www.wikipedia.com www.allaboutcircuits.com www.electrical4u.com Books Refered FUNDAMENTALS OF DIGITAL CIRCUITS By A. ANAND KUMAR
- 33. Thank You...