Line Encoding

Line encoding is the process of transformation of binary information into a format suitable for transmission through a digital communication channel.

Biphase-L Encoding

Biphase-L Encoding (also known as Manchester Encoding) is a type of line encoding.  This encoding uses transition at the middle of each bit interval.

0 is represented by –ve to +ve transition

1 is represented by +ve to –ve transition

Advantages and Properties of Biphase-L Encoding

DC Component: In Biphase-L encoded signal, each bit gives a 0 and a 1.  Therefore the number of 0’s and 1’s is equal.  Using bipolar encoding (1 => +V and 0 => -V) the DC component becomes zero.  This is very necessary when the signal is passing through a transmission system which does not allow DC to pass.  A zero DC component may also be necessary in some receiver systems.

Self Synchronization: In a Biphase-L encoded signal, at least one transition takes place for each transmitted bit.  This allows for easy clock recovery and thus Biphase-L encoded signals are self-synchronizing.

Error Detection: If a transition does not take place in the middle of received bit then some error must have occurred in the transmission of that bit.  In that case the received bit can be discarded.

Bandwidth: Maximum transition frequency of Biphase-L encoded signal is twice that of the original signal.  Biphase-L encoded signal thus requires twice the bandwidth as compared to original signal.

My Design of a Biphase-L Modem

Transmitter

Received data is first synchronized with the –ve transitions of transmitter clock (frequency = bit rate) using a D-Flip Flop.  This synchronized data is then ex-ored with the clock.  A Biphase-L signal is generated.

Receiver