TTL classification and TTL XOR Gate
- 1. TTL Classification and TTL XOR Gate
- 2. Different logic families : • RTL(Resistor Transistor Logic) • DTL(Diode Transistor Logic) • TTL(Transistor Transistor Logic) • ECL(Emitter Coupled Logic) • CMOS(Complementary Metal Oxide Semiconductor Logic) Out of these RTL and DTL are rarely used.
- 3. • It is a logic family consisting completely of bipolar junction transistors (BJT) and resistors. • the logic gating function and the amplifying function are performed What is TTL ?
- 4. History • It was build in 1961 by James L Bui. • Commercially used in logic design in 1963. • Commercially it starts with the 74 series like the 7404, 74S86 etc.
- 5. Features of TTL Family: • Logic low level : 0 or 0.2V. • Logic high level : 5V. • Typical fan out of 10. It means it can support at most 10 gates at its output. • A basic TTL device draws a power of almost 10mW. • Average propagation delay : 9ns. • Noise margin : 0.4V.
- 6. TTL Applications: • Used in controller application for providing 0 to 5Vs • Used as switching device in driving lamps and relays • Used in processors of mini computers like DEC VAX • Used in printers and video display terminals
- 7. Sub- families • 7 series of TTL 54-/74-logic family • different speed and lower dissipation characteristics : Bipolar Prefix Standard TTL. 7400 series Low - power TTL 74L00 series High -speed TTL 74H00 series Schottky TTL 74S00 series Low power Schottky TTL (LS) 74LS00 series Fast (F) and Advanced Schottky (AS) 74AS00 series Advanced Low power Schottky TTL 74ALS00 series Fast TTL 74F00 series
- 8. Characteristics 74 74S 74LS 74 AS 74 ALS 74 F Propagation delay (ns) 9 3 9.5 1.7 4 3 Power Dissipation (mW) 10 20 2 8 1.3 6 Speed-power product (pJ) 90 60 19 13.6 4.8 18 Fan-out 10 20 20 40 20 33
- 9. Fundamental TTL gate Inputs both logical ones : multiple emitter transistor – reverse-active mode. An approximately constant current flows from the positive rail, through the resistor and into the base of the current passes through the base-emitter junction of the output transistor, allowing it to conduct and pulling the output voltage low (logical zero). One input logical zero : current flows out of this input . no current flows through the base of the output transistor, and the output voltage becomes high (logical one).
- 10. Classification of TTL: • Based on output • Open Collector Output : With any of the input at logic low, voltage drop across the base of Q1 is around 0.9V, not enough for the transistors Q2 and Q3 to conduct. Thus output is either floating or Vcc, i.e. High level. when all inputs are high, transistor Q2 and Q3 get enough base current and are in saturation mode. Output is at logic low.
- 11. APPLICATIONS • It is used in 3 major applications – In driving lamps or relays – In performing wired logic – In construction of a common bus system
- 12. Totem Pole Output : • adds to this a "totem-pole" (“push-pull") output. • 2 n-p-n transistors Q3 and Q4, • lifting" diode D1 and • resistor R3=130 ohm , • Advantage : - low output resistance at output logical "1“ - results in reduction of propagation delay. • Disadvantage : - no more than 3.5 V of the output logical "1"
- 13. • When V2 is off, V4 is off, V3 operates in active region as a voltage follower producing high output voltage (logical "1"). • When V2 is "on", it activates V4, driving low voltage (logical "0") to the output.
- 14. Three state Gate: • It provides 3 state output. • "enable" input is high - normal operation of the gate. • "enable" is low -both output transistors are cutoff.
- 17. REFERENCES • https://www.elprocus.com/transistor- transistor-logic-ttl/ • https://en.wikipedia.org/wiki/7400_series • http://www.csee.wvu.edu/digital/book/chap ters/TTL.pdf • Microelectronic Circuit – Sedra Smith • https://en.wikipedia.org/wiki/Bipolar_juncti on_transistor#Regions_of_operation