Explain a TTL NAND gate and its operation, Computer Engineering

Give the circuit of a TTL NAND gate and explain its operation in brief.


Operation of TTL NAND Gate: Fig.(d) Demonstrates a TTL NAND gate with a totem pole output.   The    totem pole output implies that transistor T4 sits atop T3 in order to give low output impedance.  The low output impedance means a short time constant RC therefore the output can change rapidly from one state to the other. T1 is a multiple type emitter transistor. Such transistor can be thought of like a combination of various transistors along with a common collector and base. Multiple emitter transistors along with about 60 emitters have been developed. In this figure, T1 has 3 emitters thus there can be three inputs A, B, C. The transistor T2 functions as a phase splitter since the emitter voltage is out of phase along with the collector voltage. The transistors T3 and T4 by the totem pole output, the capacitance CL shows the stray capacitance and so on. The diode D is added to make sure that T4 is cut off while output is low. The voltage drop of diode D remains the base-emitter junction of T4 reverse biased therefore only T3 conducts while output is low. The operation can be described briefly by three conditions as specified below:

Condition 1: At least one input is low (that is, 0).  Transistor T1 saturates. Thus, the base voltage of T2 is almost zero. T2 is cut off and forces T3 to cut off.  T4 functions as an emitter follower and couples a high voltage to load. Output is high (that is Y=1).

Condition 2: Each input is high. The emitter base junctions of T1 are reverse biased. The collector base junction of T1 is forward biased. Therefore, T1 is in reverse active mode. The collector current of T1 flows in reverse direction. Because this current is flowing in the base of T2, the transistors T2 and T3 saturate and then output Y is low.

Condition 3: The circuit is operating under II while one of the inputs becomes low. The consequent emitter base junction of T1 starts conducting and T1 base voltage drops to a low value.  Thus, T1 is in forward active mode. The high collector current of T1 shifts the stored charge in T2 and T3 and hence, T2 and T3 go to cut-off and T1 saturates and then output Y returns to high.

1437_Logic Diagram of TTL NAND Gate with Totem Pole Output.png

Fig.(d) Logic Diagram of TTL NAND Gate with Totem Pole Output

Posted Date: 5/4/2013 12:46:03 AM | Location : United States

Related Discussions:- Explain a TTL NAND gate and its operation, Assignment Help, Ask Question on Explain a TTL NAND gate and its operation, Get Answer, Expert's Help, Explain a TTL NAND gate and its operation Discussions

Write discussion on Explain a TTL NAND gate and its operation
Your posts are moderated
Related Questions
Q. Data Alignment in Arrays? Arrays are aligned to templates by ALIGN directive. ALIGN directive is used to align elements of various arrays with one another denoting that they

The defining traits of an object-oriented language are: * Encapsulation * Inheritance * Polymorphism

Q. Explain Cell Spacing and Cell Padding? Couple of attributes known as CELLSPACING and CELLPADDING. Both are part of tag. CELLPADDING is the amount of space between

Identify three specific weaknesses in the design of the websites, derived from your analyses within Questions Part (c) and/or Question Part (a). There should be at least one weakne

Question: (a) Differentiate between local variables and global variables in Lingo programming. (b) Using examples differentiate between deleteProp() and deleteAt() function

Problem: A company requires a software application to calculate the weekly payment for its employees. The information about the employees (employees' data) is kept in a file.

Efficiency The effectiveness of pipeline can be measured the same as the ratio of busy time span to total time span counting the idle time. Let c be clock period of a pipeline

Define the Character Set of C Language? C uses the lower case letter a to z, the upper case letters A to Z, the digits 0 to 9 and certain characters as building blocks to form

Explain File Transfer Protocol . FTP is utilized to exchange files among computer accounts, to transfer files among an account and a desktop computer (upload) or to access softw

Unit Resolution: By assuming that we knew the sentence as "Tony Blair is prime minister or may the moon is made of blue cheese", is true or we later found out that the moon is