transistor transistor logic
- 2. CONTAIN: 7400 TTL series. Two input TTL-NAND Gate. Totem-pole output stage of TTL. Advantages –disadvantages of totem-pole. Clamping diodes. 5400 series. Advantages –disadvanges of TTL.
- 3. 7400 TTL Series o TTL ICs first developed in 1965 and they are known as “standard TTL” . This version of TTL circuit is not available now. o TTL family use only transistor to perform the basic logic operations. o The standard TTL is improved to a great extent over the year. o TTL devices are still used as “glue” logic which connects more complex devices in digital system.
- 4. Two Input TTL-NAND Gate The first, let us replace transistor Q1 by its equivalent circuits. A and B are the input terminals. The i/p voltage A and B can be either low (zero volts ideally) or High (+Vcc ideally). A and B both low : If A and B both are connected to ground, then both the B-E junction of the transistor T1 are forward biased.
- 5. Totem – pole Output Stage of TTL The arrangement of Q1 and Q2 on the output side of a TTL NAND gate is called the totem-pole arrangement. In this circuit, the three output component Q1,Q2 and diode D1 are stacked one on the top of the other in the form of totem-pole. At any time, only one of them will be conducting. The Totem-pole output is also known as Active pull- up.
- 6. Advantages and Disadvantages of Totem pole output Advantages: 1. External pull up resistor is not required 2. Operating speed is high Disadvantages: Output of two gates cannot be tied together
- 7. Clamping Diodes The TTL input should not be subjected in negative voltage. If voltage transition are applied at the input,then there is a possibility of ringing. Due to ringing the input will be subjected to negative voltages. To suppress this ringing, clamping diodes are generally connected externally in all the TTL circuits. This are fast recovery diodes. They are forward during the negative half cycles of the ringing sinusoidal waveform. Hence the negative input voltage will be restricted(clamped)to -0.7 volts approximately.
- 9. 54000 Series The devices of 5400 series oprate over the temperature range of -55 to 125˚c and over the suppl voltage range of 4.5 to 5.5 volts. 5400 TTL series developed specially for the milatry applications.
- 10. ADVANTAGES of TTL TTL circuit are fast. Low propagation delay. Power dissiparation is not dependent on frequency. Compatibale to all the other families. Latch ups do not take place. These are not susceptible to the damage due to static charges.
- 11. Disadvantages of TTL Large power dissipation. Less component density. Can operate only on +5 V power supply. Poor noise immunity.
Editor's Notes
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