Saturday, July 30, 2011

Most Common ECE Technical Questions

  1. What is meant by D-FF?(D-flip flop stands for Delay flip-flop, it delays input by one clock pulse)
  2. What is the basic difference between Latches and Flip flops?(Latches are monostable and flip-flops are bistable)
  3. What is a multiplexer?(It is used to multiplex data from different sources normally used in TDM)
  4. How can you convert an SR Flip-flop to a JK Flip-flop?
  5. How can you convert an JK Flip-flop to a D Flip-flop?( Connect J to D and K to not(D))
  6. What is Race-around problem? How can you rectify it?( Race around condition occurs in a JK flip-flop when both the inputs are set to '1', it can be rectified using edge-triggered flip-flop or using master-slave flip-flops)
  7. Which semiconductor device is used as a voltage regulator and why?
  8. What do you mean by an ideal voltage source?
  9. What do you mean by zener breakdown and avalanche breakdown?( zener breakdown takes place when very high voltage is applied to the diode this results in very high reverse current, as voltage is further increased minority carriers gain further momentum and strike atoms releases more carriers, which results in further increase in temp. It becomes vicious cycle and leads to avalanche breakdown or on other words "thermal runaway".
  10. What are the different types of filters?( analog filters n digital filters not sure wht u meant)
  11. What is the need of filtering ideal response of filters and actual response of filters?
  12. What is sampling theorem?( sampling frequency should be atleast twice the maximum freq present in the signal)
  13. What is impulse response?( response given by a digital system when impulse signal is applied to it. Used to find out stability of system)
  14. Explain the advantages and disadvantages of FIR filters compared to IIR counterparts.
  15. What is CMRR? Explain briefly.( Common mode rejection ratio)
  16. What do you mean by half-duplex and full-duplex communication? Explain briefly.( half-duplex: either sender or receiver can use the channel at one time eg walky-talky and full-duplex: sender or receiver or both can use the channel at one time eg telephone)
  17. Which range of signals are used for terrestrial transmission?
  18. What is the need for modulation?
  19. Which type of modulation is used in TV transmission?( video signal: vestigial side band modulation and audio signal: FM)
  20. Why we use vestigial side band (VSB-C3F) transmission for picture?( why not DSBSC: large bandwidth req.why not SSBSC: To over come distortion by filters used at receivers thus demodulation becomes complex hence costly)
  21. When transmitting digital signals is it necessary to transmit some harmonics in addition to fundamental frequency?( yup but not sure why)
  22. For asynchronous transmission, is it necessary to supply some synchronizing pulses additionally or to supply or to supply start and stop bit?( for asyn tx it is necessary to use start and stop bits as no common clock is there)
  23. BPFSK is more efficient than BFSK in presence of noise. Why?
  24. What is meant by pre-emphasis and de-emphasis?( used in TV Tx for voice signal not sure why)
  25. What do you mean by 3 dB cutoff frequency? Why is it 3 dB, not 1 dB?
  26. What do you mean by ASCII, EBCDIC?

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