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what is Clock Synchronization


With digital transmission, one problem that continually arises is clock synchronization.

The receiver must be able to determine when one bit time ends and the next one starts, so

that it samples one pulse, rather than part of one pulse and part of the next.

Note: quartz clocks are not accurate enough. Eventually, the sender and receiver’s clock

will drift apart.

Possibilities:

1. include timing information in the data signal

2. use a separate channel (e.g., wire) to transmit timing information

Manchester encoding is one technique that provides clocking information. The encoding

splits each sampling unit into 2 halves where:

 a binary 1″ is sent as a high-low voltage sequence

 a ” is sent as a low-high sequence

 because each sampling time contains one transition, the receiver can easily

synchronize its clock to the sender’s.

In a related technique, di erential Manchester encoding, a 1″ bit is indicated by theĀ absence of a transition at the start of the bit time, while a ” is indicated by the presenceĀ of a transition.

Drawback of Manchester encoding:

 half the bandwidth is wasted because it takes two transitions to represent one bit

Advantages:

 reduced complexity of transmitter and receiver components





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