Instead of diodes like D1X andD1Y, these devices use a multiple-emitter transistorQ1 to perform logic. Notice that there is no transistor Q1 in Figure TTL-1,but the other transistors are named in a way that’straditional some TTL devices do in fact have atransistor named Q1. Output stagetotem-pole outputpush-pull output A TTL inverter is designed as a 1-input NANDgate, omitting diodes D1Y and D2Y in Figure TTL-1. Commercially available TTL NANDgates have as many as 13 inputs.

TTL NAND gates can bedesigned with any desired number of inputs simply by changing the number ofdiodes in the diode AND gate in the figure. The gate does indeed perform the NAND function, with thetruth table and logic symbol shown in (b) and (c). The functional operation of the TTL NAND gate is summarized inFigure TTL-2(a). Similar to the p-channel and n-channel transistors in CMOS, Q4 and Q5provide active pull-up and pull-down to the HIGH and LOW states, respectively.

The TTL output stage is sometimes called a totem-pole or push-pulloutput. The output stage has two transistors, Q4 and Q5, only one of which is on atany time. Depending on whether the diode AND gate producesa “low” or a “high” voltage at VA, Q2 is either cut off or turned on. Transistor Q2 and the surrounding resistors form a phase splitter thatcontrols the output stage. Such negative excursions may occur on HIGH-to-LOW input transi-tions as a result of transmission-line effects, discussed in Section Zo. Clamp diodes D2X and D2Y do nothing in normaloperation, but limit undesirable negative excursions on the inputs to a singlediode-drop. The circuit’s operation is bestunderstood by dividing it into the three parts that are shown in the figure anddiscussed in the next three paragraphs:ĭiode AND gateand input protection Phase splitter Output stageįigure TTL-1Circuit diagram of 2-input LS-TTL NAND gate.ĭiodes D1X and D1Y and resistor R1 in Figure TTL-1 form a diode ANDgate, as in Section Diode.2. The NAND function is obtained by combining a diodeAND gate with an inverting buffer amplifier. TTL.1 Basic TTL NAND GateThe circuit diagram for a 2-input LS-TTL NAND gate, part number 74LS00, isshown in Figure TTL-1. We’ll use the following definitions of LOW andHIGH in our discussions of TTL circuit behavior: TTL families use basically the same logic levels as the TTL-compatibleCMOS families in Section 3.8. The circuit examples in this section arebased on a representative TTL family, Low-power Schottky (LS or LS-TTL). TTL: Transistor-Transistor-Logic TopicsThe most commonly used bipolar logic family is transistor-transistor logic.Actually, there are many different TTL families, with a range of speed, powerconsumption, and other characteristics. No portion of this material may be reproduced, in any form or by any means, without permission in writing by the publisher. This material is protected under all copyright laws as they currently exist. 2006 Pearson Education, Inc., Upper Saddle River, NJ. Supplementary material to accompany Digital Design Principles and Practices, Fourth Edition, by John F. Q5 V CC = +5 V R1 20 k Ω D1X D1Y D2X D2Y R2 8 k Ω R4 1.5 k Ω R3 12 k Ω Q2 X Y Z R5 120 Ω Q3 Q4 R6 4 k Ω R7 3 k Ω Q6 D3 D4 Diode AND gate and input protection Phase splitter Output stage V A Figure TTL-1 Circuit diagram of 2-input LS-TTL NAND gate. The circuit’s operation is best understood by dividing it into the three parts that are shown in the figure and discussed in the next three paragraphs: The NAND function is obtained by combining a diode AND gate with an inverting buffer amplifier. TTL.1 Basic TTL NAND Gate The circuit diagram for a 2-input LS-TTL NAND gate, part number 74LS00, is shown in Figure TTL-1.

We’ll use the following definitions of LOW and HIGH in our discussions of TTL circuit behavior: LOW 0–0.8 volts. TTL families use basically the same logic levels as the TTL-compatible CMOS families in Section 3.8. The circuit examples in this section are based on a representative TTL family, Low-power Schottky (LS or LS-TTL). Actually, there are many different TTL families, with a range of speed, power consumption, and other characteristics. TTL: Transistor-Transistor-Logic Topics The most commonly used bipolar logic family is transistor-transistor logic. Transistor-Transistor-Logic Topics TTL–1 Supplementary material to accompany Digital Design Principles and Practices, Fourth Edition, by John F.

Ttl transistor diagram and gate