GATE 1999 ECE Video Solution on Digital Circuits (Digital Electronics)

1. The logical expression Y = A + A’B is equivalent to
a. AB
b. A’B
c. A’ + B
d. A + B

2. A Darlington emitter follower circuit is sometimes used in the output stage of a TTL gate, in order to
a. Increase its IOL
b. Reduce its IOH
c. Increase its speed of operation
d. Reduce power dissipation

3. Commercially available ECL gates uses two ground lines and one negative power supply in order to
a. Reduce power dissipation
b. Increase fan-out
d. Eliminate the effect of power line glitches or the biasing circuit

4. The resolution of a 4 bit counting ADC is 0.5 volts. For an analog input of 6.6 volts, the digital output of the ADC will be
a. 1011
b. 1101
c. 1100
d. 1110

5. The minimized form of the logical expression

6. For a binary half – subtractor having two inputs A and B, the correct set of logical expressions for the outputs D (= A minus B) and X (= borrow) are

7. The ripple counter shown in the given figure is works as a

a. Mod – 3 up counter
b. Mod – 5 up counter
c. Mod – 3 down counter
d. Mod – 5 down counter

8. If CS = A15’A14A13 is used as the chip select logic of a 4K RAM in an 8085 system, then its memory range will be
a. 3000 – 3FFFFH
b. 7000 – 7FFFH
c. 5000 – 5FFFH and 6000 – 6FFFH
d. 6000 – 6FFFH and 7000 – 7FFFH

9. The circuit diagram of a synchronous counter is shown in the given figure. Determine the sequence of states of the counter assuming that the initial state is ‘000’. Give your answer in a tabular form showing the present state QA, QB, QC, J-K inputs (JA, KA, JB, KB, JC, KC) and the next state QA+, QB+, QC+. From the table, determine the modulus of the counter.

10. In a certain application, four inputs A, B, C, D (both true and complement forms available) are fed to logic circuit, producing an output F which operates a relay. The relay turns on when F(ABCD) = 1 for the following states of the inputs (ABCD): ‘0000’, ‘0010’, ‘0101’, ‘0110’, ‘1101’ and ‘1110’. States ‘1000’ and ‘1001’ do not occur, and for the remaining states, the relay is off. Minimize F with the help of a Karnaugh map and realize it using a minimum number of 3 input NAND gates.

11. An 8085 assembly language program is given below.

Solution :

1. Where is the solution of last question..????

2. In certain application, four inputs A, B, C, D (both true and complement forms available)are fed to logic circuit, producing an output F which operates a relay. The relay turns on when F(ABCD)=1 for the binary representation of your VTU number ( convert your VTU number into binary and separate them into 4 bits) and for the remaining states, the relay is off.
Minimize F with the help of a Tabulation method.
Find the best minimal solution for the Maxterms.
Also convert the obtained minimal expression into Canonical POS form.

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