---

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 ???          Obvious answer: 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 !)