CS485 Sylabus

Encoding/decoding digital data using digital signals

• Digital data

• Digital data:

• Digital data = discrete values

Example:

 12, 45, -67 3.14, 4.12, ....

• Fact:

• Digital values can be converted into a binary representation

Example:

 12    ↔    00001100

• Digital signal

• Digital signal:

• Digital signal = a signal with finite number of discrete levels

Example: a two level digital signal

• Digital data transmission with digital signals

• Transmitting digital data using digital signal:

• Digital data: 0101010101

• Digital signal to relay this digital data:

• The missing ingredient in digital transmission

\$64,000 questions:

• Suppose you receive this digital signal:

Question:

 What was the data transmitted ???

 ``` 010101010101 ```

Is this the only answer ?????

• Decoding a digital signal

• Illustrative example:

• Suppose you received the following digital signal:

Question:

 What was the digital data that is encoded by this signal ???

• An obvious answer is 010101010101

because:

• An not so "obvious" answer is 001100110011001100110011

because:

• Answer to the \$64,000 question:

 You need to know the transmission rate (of the digital signal) in order to decode (= determine the result) a digital signal !!!!!

• Clock signal

• Fact:

 Transmission rate (= speed) in electronic devices are controlled by a clock signal

• Clock signal:

• Clock signal = a periodic wave of 0,1 transitions at a fixed frequency

Example:

• Clock signal generation circuits:

 Clock generator = a circuit that produces a timing signal for use in driving (synchronizing) a circuit's operation. See: Wikiopedia

• Transmitting and decoding digital signals

• How to use a clock in digital communication:

• Requirement:

 Both the sender and the receiver must use a clock with the same frequency

I.e.:

 Sender and receiver will operate at the same speed !!!

• Transmission method used by the sender:

• Transmit the signal (= 0 or 1) for 1 clock period

Example:

• Decoding (= reception) method used by the receiver:

• Read the received signal at the middle point of a clock period

Example:

• Very important:

 Sender and receiver that uses digital signaling to communicate with each other must use the same clock frequency !!! (Otherwise, you will have reception errors !)