Digital Design Interview Questions - 4

1. Design 2 input AND, OR, and EXOR gates using 2 input NAND gate.
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2. Design a circuit which doubles the frequency of a given input clock signal.
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3. Implement a D-latch using 2x1 multiplexer(s).
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4. Give the excitation table of a JK flip-flop.
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5. Give the Binary, Hexadecimal, BCD, and Excess-3 code for decimal 14.
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6. What is race condition?
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7. Give 1's and 2's complement of 19.
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8. Design a 3:6 decoder.
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9. If A*B=C and C*A=B then, what is the Boolean operator * ?
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10. Design a 3 bit Gray Counter.
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Verilog Interview Questions - 3

1. How are blocking and non-blocking statements executed?
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2. How do you model a synchronous and asynchronous reset in Verilog?
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3. What happens if there is connecting wires width mismatch?
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4. What are different options that can be used with $display statement in Verilog?
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5. Give the precedence order of the operators in Verilog.
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6. Should we include all the inputs of a combinational circuit in the sensitivity list? Give reason.
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7. Give 10 commonly used Verilog keywords.
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8. Is it possible to optimize a Verilog code such that we can achieve low power design?
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9. How does the following code work?
wire [3:0] a;
always @(*)
begin
case (1'b1)
a[0]: $display("Its a[0]");
a[1]: $display("Its a[1]");
a[2]: $display("Its a[2]");
a[3]: $display("Its a[3]");
default: $display("Its default")
endcase
end
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10. Which is updated first: signal or variable?
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VLSI Interview Questions - 5

This sections contains interview questions related to LOW POWER VLSI DESIGN.

1. What are the important aspects of VLSI optimization?
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2. What are the sources of power dissipation?
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3. What is the need for power reduction?
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4. Give some low power design techniques.
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5. Give a disadvantage of voltage scaling technique for power reduction.
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6. Give an expression for switching power dissipation.
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7. Will glitches in a logic circuit cause power wastage?
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8. What is the major source of power wastage in SRAM?
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9. What is the major problem associated with caches w.r.t low power design? Give techniques to overcome it.
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10. Does software play any role in low power design?
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Digital Design Interview Questions - 1

1. How do you convert a XOR gate into a buffer and a inverter (Use only one XOR gate for each)?
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2. Implement an 2-input AND gate using a 2x1 mux.
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3. What is a multiplexer?
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4. What is a ring counter?
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5. Compare and Contrast Synchronous and Asynchronous reset.
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6. What is a Johnson counter?
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7. An assembly line has 3 fail safe sensors and one emergency shutdown switch.The line should keep moving unless any of the following conditions arise:
(1) If the emergency switch is pressed
(2) If the senor1 and sensor2 are activated at the same time.
(3) If sensor 2 and sensor3 are activated at the same time.
(4) If all the sensors are activated at the same time
Suppose a combinational circuit for above case is to be implemented only with NAND Gates. How many minimum number of 2 input NAND gates are required?
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8. In a 4-bit Johnson counter How many unused states are present?
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9. Design a 3 input NAND gate using minimum number of 2 input NAND gates.
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10. How can you convert a JK flip-flop to a D flip-flop?
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VLSI Interview Questions - 4

1. Why is the number of gate inputs to CMOS gates (e.g. NAND or NOR gates)usually limited to four?
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2. What are static and dynamic power dissipation w.r.t to CMOS gate?
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3. Draw Vds-Ids curve for a MOSFET. Now, show how this curve changes (a) with increasing Vgs (b) considering Channel Length Modulation.
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4. Which is fastest among the following technologies: CMOS, BiCMOS, TTL, ECL?
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5. What is a transmission gate, and what is its typical use in VLSI?
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6. Draw the cross section of nMOS or pMOS.
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7. What should be done to the size of a pMOS transistor inorder to increase its threshold voltage?
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8. Explain the various MOSFET Capacitances and their significance.
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9. On what factors does the resistance of metal depend on?
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10. Draw the layout a CMOS NAND gate.
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VLSI Interview Questions - 3

1. Explain the voltage transfer characteristics of a CMOS Inverter.
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2. What should be done to the size of a nMOS transistor in order to increase its threshold voltage?
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3. What are the advantages of CMOS technology?
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4. Give the expression for CMOS switching power dissipation.
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5. Why is static power dissipation very low in CMOS technology when compared to others?
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6. What is velocity saturation? What are its effects?
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7. Why are pMOS transistor networks generally used to produce high signals, while nMOS networks are used to product low signals?
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8. Expand: DTL, RTL, ECL, TTL, CMOS, BiCMOS.
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9. On IC schematics, transistors are usually labeled with two, or sometimes one number(s). What do each of those numbers mean?
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10. How do you calculate the delay in a CMOS circuit?
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VLSI Interview Questions - 2

1. Explain the various MOSFET capacitance and give their significance.
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2. What is the fundamental difference between a MOSFET and BJT ?
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3. What is meant by scaling in VLSI design? Describe various effects of scaling.
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4. What is early effect?
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5. Compare and contrast analog and digital design.
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6. What are various types of the number notations? Explain them.
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7. Why are most interrupts active low?
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8. Which is better: synchronous reset or asynchronous reset signal?
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9. What is meant by 90nm technology?
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10. Compare enhancement and depletion mode devices.
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Digital Design Interview Questions - 2

1. What are the differences between a flip-flop and a latch?
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2. What is the difference between Mealy and Moore FSM?
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3. What are various types of state encoding techniques? Explain them.
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4. Define Clock Skew , Negative Clock Skew, Positive Clock Skew.
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5. Give the transistor level circuit of a CMOS NAND gate.
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6. Design a 4-bit comparator circuit.
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7. Design a Transmission Gate based XOR. Now, how do you convert it to XNOR (without inverting the output)?
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8. Define Metastability.
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9. Compare and contrast between 1's complement and 2's complement notation.
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10. Give the transistor level circuit of CMOS, nMOS, pMOS, and TTL inverter gate.
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VLSI Interview Questions - 1

1. How does a MOSFET works?
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2. Explain various types of digital design technologies ( CMOS, TTL etc).
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3. What is threshold voltage?
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4. What is noise margin?
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5. Explain the three modes of operation of a MOSFET.
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6. What is channel-length modulation?
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7. What is doping?
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8. What is body effect?
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9. Give various factors on which threshold voltage depends.
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10. Explain nMOS and pMOS.
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Digital Design Interview Questions - 3

1. What are set up time and hold time constraints?
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2. Give a circuit to divide frequency of clock cycle by two.
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3. Design a divide-by-3 sequential circuit with 50% duty circle.
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4. Explain different types of adder circuits.
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5. Give two ways of converting a two input NAND gate to an inverter.
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6. Draw a Transmission Gate-based D-Latch.
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7. Design a FSM which detects the sequence 10101 from a serial line without overlapping.
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8. Design a FSM which detects the sequence 10101 from a serial line with overlapping.
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9. Give the design of 8x1 multiplexer using 2x1 multiplexers.
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10. Design a counter which counts from 1 to 10 ( Resets to 1, after 10 ).
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