296 + Interview Questions in Digital Electronics in Electronics and Communication Engineering Page 1 InterviewSolution

1.	Four inputs A, B, C, D are fed to a NOR gate. The output of NOR gate is fed to an inverter. The output of inverter is
Answer» Output = = A + B + C + D.

Discussion

2.	For the logic circuit of the given figure, the minimized expression is
Answer» + A + C = A + B + C + A + C = A + C + B =

Discussion

3.	A 4 bit synchronous counter uses flip flops with a delay time of 15 ns each. The time required for change of state is
Answer» In a synchronous counter clock input is applied to all flip flops simultaneously. Hence total delay time is 15 ns.

Discussion

4.	110.11 x 110 = __________
Answer» 110.11 =6.75 and 110 = 6 and 6.75 x 6 = 40.5 in decimal.

Discussion

5.	Y = A + B is the same as
Answer» Verify by preparing truth table.

Discussion

6.	The inputs to a NAND gate are as shown in the given figure. The waveform of output is
Answer» NAND gate gives high output when both inputs are Low.

Discussion

7.	In the decimal number 27, the digital 2 represents
Answer» 2 x 10 = 20.

Discussion

8.	In the circuit of the given figure, V =
Answer» Transistor is off and circuit current is zero.

Discussion

9.	A parallel in-parallel out shift register can be used to introduce delay in digital circuits.
Answer» No time delay in this shift register since all bits are loaded and read simultaneously.

Discussion

10.	E7F6 = __________ .
Answer» E7 F6 in hexadecimal = 14 x 163 + 7 x 162 + 15 x 16 + 6 = 59382 in decimal.

Discussion

11.	A 14 pin AND gate IC has __________ AND gates.
Answer» Each AND gates requires 3 pins, 2 inputs and one output, 1 supply pin and 1 ground pin. Hence 4 AND gates.

Discussion

12.	For the design of a sequential circuit having 9 states, minimum number of memory elements required is
Answer» 23 = 8 and 24 = 16. Hence minimum of 4 memory elements.

Discussion

13.	ICs are
Answer» Op-amp is an analog IC.

Discussion

14.	The hexadecimal number 'A0' has the decimal value
Answer» 'Ao' = 10 x 161 + 0 = 160.

Discussion

15.	A 4 bit ripple counter is in 0000 state. The clock pulses are applied and then removed. The counter reads 0011. The number of clock pulses which have occurred are
Answer» After 16 pulses the counter resets. 0011 is 3. Hence clock pulses can be 3 or 3 + 16 or 3 + 16 + 16.

Discussion

16.	If an analog voltage is expressed in binary using 4 bits, each successive binary count would represent
Answer» Since 1111= decimal 15, each successive binary count represent 1/15 of total voltage.

Discussion

17.	In a 4 input AND gate, the total number of High outputs for 16 input states are
Answer» In only one combination are all inputs high.

Discussion

18.	A digital system is required to amplify a binary encoded audio signal. The user should be able to control the gain of the amplifier from a minimum to a maximum in 100 increments. The minimum number of bits required to encode, in straight binary is,
Answer» Let 6 bit required = 26 = 64, which indicate 64 increment. If 7 bit = 27 = 128, for 100 increment, 7 bit required.

Discussion

19.	A 4 bit transistor register has output voltage of high-low-high-low. The binary number stored and its decimal equivalent are
Answer» 1010 in binary and 8 + 2 = 10 in decimal.

Discussion

20.	Hexadecimal number F is called to octal number
Answer» F = 15 in decimal notation = 17 in octal notation (8 + 7 = 15).

Discussion

21.	A half adder can be used only for adding
Answer»

Discussion

22.	Symmetrical square wave of time period 100 μs can be obtained from square wave of time period 10 μs by using
Answer» Frequency has to be divided by 10.

Discussion

23.	The initial state of a Mod-16 counter is 0110. After 37 clock pulses the state of counter will be
Answer» After 37 clock pulses the state will be the same as after (37 - 32), i.e., 5 clock pulses. 6 + 5 = 11. Hence 1011.

Discussion

24.	The circuit in the figure is has two CMOS-NOR gates. This circuit functions as a
Answer» It is simple monostable multivibrator.

Discussion

25.	A 6 bit DAC uses binary weighted resistors. If MSB resistor is 20 k ohm, the value of LSB resistor is
Answer» Resistances are R, 2R, 4R, 8R, 16R and 32R. LSB resistance = 32R = 32 x 20 = 640 K ohm.

Discussion

26.	A 6 bit dual slope A/D converter uses a reference of -6v and a 1 MHz clock. It uses a fixed count of 40 (101000). Then, what will be input, if the output register shows 100111 at the end of conversion.
Answer» I/P voltage and reference voltage arc of opposite polarity.

Discussion

27.	In the TTL circuit in the figure, S to S are select lines and X to X are input lines. S and X are LSBs. The output Y is
Answer» The MUX is made up of TTL circuit. For TTL circuit open terminal is taken high, since S2 select line is connected to OR gate whose one terminal connected to C and the other is open (high) so OR gate output is S2 = 1 + C = 1. S2 = 1 S1(B) S0(A) Y 1 0 0 0 1 0 1 1 1 1 0 1 1 1 1 0 Y = S0⊕S1 => A⊕B.

Discussion

28.	A 12 bit ADC is employed to convert an analog voltage of zero to 10 volts. The resolution of the ADC is
Answer» Full scale measurement range = 0 to 10 volts. ADC resolution is 12 bits: 2^12 = 4096 quantization levels. ADC voltage resolution is: (10-0)/4096 = 0.00244 volts = 2.44 mV.

Discussion

29.	A device which converts BCD to seven segment is called
Answer» Decoder converts binary/BCD to alphanumeric.

Discussion

30.	In 2's complement representation the number 11100101 represents the decimal number
Answer» A = 11100101. Therefore A = 00011010 and A' = A + 1 = 00011011 = 16 + 8 + 2 + 1 = 27. Therefore A = -27.

Discussion

31.	A decade counter skips
Answer» A decade counter counts from 0 to 9. It has 4 flip-flops. The states skipped are 10 to 15 or 1010 to 1111.

Discussion

32.	BCD input 1000 is fed to a 7 segment display through a BCD to 7 segment decoder/driver. The segments which will lit up are
Answer» 1000 equals decimal 8 Therefore all segments will lit up.

Discussion

33.	Octal number 12 is equal to decimal number
Answer» 12 in octal = 8 + 2, i.e., 10 in decimal.

Discussion

34.	Hexadecimal number E is equal to binary number
Answer» E = 14 in decimal or 1110 (8 + 4 + 2 + 0 = 14) is binary.

Discussion

35.	Decimal number 46 in excess 3 code =
Answer» Decimal 46 in excess 3 code = 46 + 33 = 79 in decimal = 0111 1001 in 4 bit binary.

Discussion

36.	A multilevel decoder is more costly as compared to single level decoder.
Answer» A multi level decoder may be cheaper than single level decoder.

Discussion

37.	EPROM can be
Answer» Both ultra violet and electric pulses are used for erasing.

Discussion

38.	A full subtractor has a total of
Answer»

Discussion

39.	A full adder adds
Answer»

Discussion

40.	For a Mod 64 parallel counter we need
Answer» 26 = 64 So we need 6 flip-flops and (6 - 2) = 4 AND gates.

Discussion

41.	If the inputs to a 2 input XOR gate are high then, the output is high.
Answer» Output is Low.

Discussion

42.	The number of select lines in a 16 : 1 multiplexer are
Answer» 24 = 16.

Discussion

43.	BCD number 1100111 = __________
Answer» 0110 = 6 and 0111 = 7 Hence 67.

Discussion

44.	The K-map for a Boolean function is shown in figure. The number of essential prime implicants for this function is
Answer» Essential Prime implicates = 4.

Discussion

45.	When microprocessor processes both positive and negative numbers, the representation used is
Answer» 2's complement representation requires simple electronic circuitry.

Discussion

46.	TTL is used in electronic calculators.
Answer» Calculators use CMOS.

Discussion

47.	A 4 bit down counter can count from
Answer» It can count from 15 to 0 or 1111 to 0000.

Discussion

48.	For the circuit of the given figure, the output equation is
Answer» The inputs A and B are ANDed. Inputs B and C' so ANDed. The outputs of two AND gates are ORed.

Discussion

49.	Using 2's complement, the largest positive and negative number which can be stored with 8 bits are
Answer» Largest positive number is 0111 111 = + 127 and largest negative number is 1000 0000 = -128.

Discussion

50.	Three Mod-16 counters are connected in cascade. The maximum counting range is
Answer» 16 x 16 x 16 = 4096.

Discussion

Explore topic-wise InterviewSolutions in .

Four inputs A, B, C, D are fed to a NOR gate. The output of NOR gate is fed to an inverter. The output of inverter is

For the logic circuit of the given figure, the minimized expression is

A 4 bit synchronous counter uses flip flops with a delay time of 15 ns each. The time required for change of state is

110.11 x 110 = __________

Y = A + B is the same as

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In the circuit of the given figure, V =

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A 4 bit ripple counter is in 0000 state. The clock pulses are applied and then removed. The counter reads 0011. The number of clock pulses which have occurred are

If an analog voltage is expressed in binary using 4 bits, each successive binary count would represent

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A digital system is required to amplify a binary encoded audio signal. The user should be able to control the gain of the amplifier from a minimum to a maximum in 100 increments. The minimum number of bits required to encode, in straight binary is,

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The initial state of a Mod-16 counter is 0110. After 37 clock pulses the state of counter will be

The circuit in the figure is has two CMOS-NOR gates. This circuit functions as a

A 6 bit DAC uses binary weighted resistors. If MSB resistor is 20 k ohm, the value of LSB resistor is

A 6 bit dual slope A/D converter uses a reference of -6v and a 1 MHz clock. It uses a fixed count of 40 (101000). Then, what will be input, if the output register shows 100111 at the end of conversion.

In the TTL circuit in the figure, S to S are select lines and X to X are input lines. S and X are LSBs. The output Y is

A 12 bit ADC is employed to convert an analog voltage of zero to 10 volts. The resolution of the ADC is

A device which converts BCD to seven segment is called

In 2's complement representation the number 11100101 represents the decimal number

A decade counter skips

BCD input 1000 is fed to a 7 segment display through a BCD to 7 segment decoder/driver. The segments which will lit up are

Octal number 12 is equal to decimal number

Hexadecimal number E is equal to binary number

Decimal number 46 in excess 3 code =

A multilevel decoder is more costly as compared to single level decoder.

EPROM can be

A full subtractor has a total of

A full adder adds

For a Mod 64 parallel counter we need

If the inputs to a 2 input XOR gate are high then, the output is high.

The number of select lines in a 16 : 1 multiplexer are

BCD number 1100111 = __________

The K-map for a Boolean function is shown in figure. The number of essential prime implicants for this function is

When microprocessor processes both positive and negative numbers, the representation used is

TTL is used in electronic calculators.

A 4 bit down counter can count from

For the circuit of the given figure, the output equation is

Using 2's complement, the largest positive and negative number which can be stored with 8 bits are

Three Mod-16 counters are connected in cascade. The maximum counting range is