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Tuesday, February 24, 2009


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.

2. Identify the circuit below, and its limitation.

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 ?

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.
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 ?

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

Design an OR gate from 2:1 MUX.(This is one of the most commonly asked interview questions)

Design an XOR gate from 2:1 MUX and a NOT gate
14. What is the difference between a LATCH and a FLIP-FLOP ?
  • 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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    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.