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Tuesday, February 24, 2009

DIGITAL DESIGN INTERVIEW QUESTIONS

1. What is the output of AND gate in the circuit below, when A and B are as in waveform? Tp is the gate delay of respective gate.
Ans. 
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2. Identify the circuit below, and its limitation.
Ans. 
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3. Referring to the diagram below, briefly explain what will happen if the propagation delay of the clock signal in path B is much too high compared to path A. How do we solve this problem if the propagation delay in path B can not be reduced ?
Ans
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4.  What is the function of a D flip-flop, whose inverted output is connected to its input ?
5.   Design a circuit to divide input frequency by 2.
6.  
What are the different types of adder implementations ?
7. What are the different types of adder implementations ?
8. Give the truth table for a Half Adder. Give a gate level implementation of it.
9. What is the purpose of the buffer in the circuit below, is it necessary/redundant to have a buffer ?
10.  What is the output of the circuit below, assuming that value of 'X' is not known ?

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11. Consider a circular disk as shown in the figure below with two sensors mounted X, Y and a blue shade painted on the disk for an angle of 45 degree. Design a circuit with minimum number of gates to detect the direction of rotation
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12. 
Design an OR gate from 2:1 MUX.(This is one of the most commonly asked interview questions)
Ans. 
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13. 
Design an XOR gate from 2:1 MUX and a NOT gate
14. What is the difference between a LATCH and a FLIP-FLOP ?
Ans. 
  • Latch is a level sensitive device while flip-flop is an edge sensitive device.
  • Latch is sensitive to glitches on enable pin, whereas flip-flop is immune to glitches.
  • Latches take less gates (also less power) to implement than flip-flops.
  • Latches are faster than flip-flops. 
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    ../images/digital/latch_ff_wv.gif

    16.    What is metastable state ? How does it occur ?  
        
     
    17.     What is metastability ?  
        
     
    18.     Design a 3:8 decoder  
        
     
    19     Design a FSM to detect sequence "101" in input sequence.  
        
     
     20    Convert NAND gate into Inverter, in two different ways.  
        
     
      21   Design a D and T flip flop using 2:1 mux; use of other components not allowed, just the mux.  
        
     
      22   Design a divide by two counter using D-Latch.  
        
     
     23    Design D Latch from SR flip-flop.  
        
     
    24     Define Clock Skew , Negative Clock Skew, Positive Clock Skew.  
        
     
     25    What is Race Condition ?  
        
     
    26     Design a 4 bit Gray Counter.  
        
     
    27     Design 4-bit Synchronous counter, Asynchronous counter.  
        
     
     28    Design a 16 byte Asynchronous FIFO.  
        
     
     29    What is the difference between an EEPROM and a FLASH ?  
        
     
      30   What is the difference between a NAND-based Flash and a NOR-based Flash ?  
        
     
     31    You are given a 100 MHz clock. Design a 33.3 MHz clock with and without 50% duty cycle.  
        
     
     32    Design a Read on Reset System ?  
        
     
      33   Which one is superior: Asynchronous Reset or Synchronous Reset ? Explain.  
        
     
      34   Design a State machine for Traffic Control at a Four point Junction.  
        
     
      35   What are FIFO's? Can you draw the block diagram of FIFO? Could you modify it to make it asynchronous FIFO ?  
        
     
    36     How can you generate random sequences in digital circuits?  


    All these are common digital interview questions which you might come across in interviews at campus level. 


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