Give the circuit of a TTL NAND gate and explain its operation in brief. Ans: 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. Fig.(d) Logic Diagram of TTL NAND Gate with Totem Pole Output Posted Date: 5/4/2013 12:46:03 AM | Location : United States

Ask an Expert

Your posts are moderated

Write your message here..

Related Questions

Explain is cgi a script or a program, The distinction is semantic. Traditio... The distinction is semantic. Traditionally, compiled executables (binaries) are known as programs, and interpreted programs are usually known as scripts. In the context of CGI, the

Menu driven program with following menu, Q.  Develop a Menu driven program ... Q.  Develop a Menu driven program with following menu: 1.  Gray code 2.  BCD 3.  Excess-3 code 4.  Exit I/P must be a valid Binary number. Fractional numbers are all

Explain bitwise operator, Bitwise Operators Like  other  operators  bit... Bitwise Operators Like  other  operators  bitwise  operators  have  rules  of  precedence  and  associativity  that determine how expressions involved them are evaluated.

Visual perception problems, In AI the process of perception is studied ... In AI the process of perception is studied as a set operations. A visual scene may be encoded by sensors and represented as matrix of intensity values. These are processed b

Give the truth table of S-R and D-flipflops, Give the truth table of S-R an... Give the truth table of S-R and D-flipflops. Ans: The Truth Table for S-R Flip-Flop is illustrated in Fig.(a) and truth table of D Flip-Flop is illustrated in Fig.(b)

Convert the decimal numbers into hexadecimal, Q Convert the following DECIM... Q Convert the following DECIMAL numbers into HEXADECIMAL, double check by converting the result HEXADECIMAL to DECIMAL. a)    24 b)   547.56

State some criterias and their effects on a database, It is possible to ent... It is possible to enter one or more criteria in the rows which can influence your database significantly. >="Callahan" this returns all the several records from Callahan to the

Explain organisations use in electronic data interchange, Explain about the... Explain about the organisations use in EDI. Organisations, which are use Electronic Data Interchange. Extensive users of Electronic Data Interchange (EDI) include: BHS:

What does realized mean, Realized mean that the component has been painted ... Realized mean that the component has been painted on screen or that is prepared to be painted. Realization can take place by invoking any of these methods. setVisible(true), show()

Calculate grade of service in a particular excahange, In a particular excha... In a particular exchange during busy hour 1200 calls were offered to a group of trunks, during this time 6 calls were lost. The average call duration being 3 minutes Calculate