Types of Conversions

Types of Conversions ™   Digital-to-Digital Conversion o    Digital-to-Digital    conversion/encoding    is    the    representation    of    digital information by digital signal o    For  Example  when  you  Tx  data  from  Computer  to  the  Printer,  both  original and transmitted data have to be digital o    In this type of encoding, 1's and 0's generated by the computer are translated into voltage pulses that can be propagated over the wire o    Figure shows the relationship between digital information, digital-to-digital encoding hardware , and the resultant digital signal Types of Digital-to-Digital Encoding ™   UNIPOLAR    Encoding is simple , with only one technique in use    Simple and Primitive    Almost Obsolete Today    Study provides introduction to concepts and problems involved with more complex encoding systems o    Digital  Transmission  system  works  by  sending  voltage  pulses  on the Tx. Medium o    One  voltage  level  stands  for  binary  0  while  the  other  stands  for binary 1 o    It is called Unipolar because it uses only one polarity o    This polarity is assigned to to one of the two binary states usually a '1' o    The other state usually a 0 is represented by zero voltage o    Figure shows the idea: 1's are encoded as +ve values, and 0's are encoded as -ve values Pros and Cons of Unipolar Encoding •     PROS -    Straight Forward and Simple -    Inexpensive to Implement •     CONS -    DC Component -    Synchronization DC Component o    Average Amplitude of a unipolar encoded signal is non-zero o    This  is  called  DC  Component  I.e.  a  component  with  zero frequency o    When  a  signal  contains  a  DC  Component,  it  cannot  travel through a Tx. Medium that cannot handle DC components Synchronization o    When the signal is unvarying, Rx. Cannot determine the beginning and ending of each bit o    Synchronization  Problem  can  occur  when  data  consists  of  long streams of 1's or 0's o    Therefore, Rx has to rely on a TIMER o    Consider we have a bit rate of the signal to be 1000bps Š    1000 bits in 1 second Š    1 bit in 0.001 second o    So if a +ve voltage lasts 0.005 sec, it reads five 1's o    Sometimes it stretches to 0.006 seconds and an extra one bit is read by the Rx Š    Solution: -    Separate Parallel Line o    Carries a clock pulse and allows receiver to resynchronize its timer to that of the signal o    Doubling no. of Tx lines increase Cost and proves uneconomical