AQA · A-Level · Physics

    Course version: 7408 · Version from Sept 2016

    Basic principles of time-division multiplexing.

    Full specification wording

    Time-division multiplexing (A-level only): Basic principles of time-division multiplexing.

    Time-division multiplexing (TDM) lets several signals share one communication channel by giving each signal the whole channel for a short, repeating slice of time.

    Checked against the AQA 7408 specification (opens in a new tab) on .

    • 4 key terms

    Study notes

    From the checked teaching notes for this specification point.

    The idea

    Time-division multiplexing (TDM) lets several signals share one communication channel by giving each signal the whole channel for a short, repeating slice of time. A multiplexer samples each input in turn, so the channel carries a rapid sequence of samples: input 1, then input 2, then input 3, then back to input 1. At the far end a demultiplexer uses the same timing to route each sample to the correct output. The samples must be taken often enough to represent each signal faithfully, and the transmitter and receiver must stay synchronised so that samples are not sent to the wrong destination. TDM is digital-friendly and is widely used in telephone networks and data links, where many conversations or data streams share one high-speed connection.

    What earns the marks

    • TDM allows multiple signals to share a single communication channel.
    • Each signal is allocated the whole channel for short, repeating time slots.
    • A multiplexer samples the input signals in a fixed sequence.
    • A demultiplexer at the receiver separates the interleaved samples using the same timing.
    • The sampling rate must be high enough to represent each signal accurately.
    • Transmitter and receiver must remain synchronised so samples reach the correct output.
    • TDM is suited to digital signals and is used in telephone and data networks.

    Common mistakes and how to put them right

    • Thinking that all signals are transmitted at the same time on the same channel.

      Put it right: Each signal uses the channel only during its own time slot.

    • Confusing TDM with frequency-division multiplexing, where signals share the channel simultaneously at different frequencies.

      Put it right: TDM separates signals in time, not frequency.

    • Ignoring the need for synchronisation between multiplexer and demultiplexer.

      Put it right: Without common timing, samples are routed to the wrong outputs.

    Exam tips

    • Sketch a simple timeline showing slots labelled A, B, C, A, B, C to make the interleaving visible.
    • State clearly that each input gets the full channel bandwidth during its slot, unlike frequency sharing.
    • Link the sampling rate to the need to reconstruct each original signal without loss of detail.

    Try the lesson

    The start of the Time-division multiplexing (A-level only): Basic principles of time-division multiplexing. lesson, made from checked teaching notes for this specification point.

    Have a go first

    In time-division multiplexing, how are several separate signals carried along one communication channel?

    Listen

    Time-division multiplexing (TDM) lets several signals share one communication channel by giving each signal the whole channel for a short, repeating slice of time. A multiplexer samples each input in turn, so the channel carries a rapid sequence of samples: input 1, then input 2, then input 3, then back to input 1. At the far end a demultiplexer uses the same timing to route each sample to the correct output. The samples must be taken often enough to represent each signal faithfully, and the transmitter and receiver must stay synchronised so that samples are not sent to the wrong destination. TDM is digital-friendly and is widely used in telephone networks and data links, where many conversations or data streams share one high-speed connection. A strong answer earns marks for these points. TDM allows multiple signals to share a single communication channel. Each signal is allocated the whole channel for short, repeating time slots. A multiplexer samples the input signals in a fixed sequence. A demultiplexer at the receiver separates the interleaved samples using the same timing. A common slip: Thinking that all signals are transmitted at the same time on the same channel. Instead, each signal uses the channel only during its own time slot. Exam tip: Sketch a simple timeline showing slots labelled A, B, C, A, B, C to make the interleaving visible.

    See it

    A top-down flowchart. Input signals lead to a box for the multiplexer sampling each input in turn, which leads to one communication channel, then to a box describing the rapid sequence of samples: input 1, input 2, input 3, back to input 1. This leads to a box for the demultiplexer using the same timing, which leads to a box for each sample being routed to the correct output. Two separate boxes feed into the chain: one stating that the transmitter and receiver must stay synchronised, with an arrow into the demultiplexer box, and one stating that the sampling rate must be high enough to represent each signal faithfully, with an arrow into the multiplexer box.
    It shows how a multiplexer samples several inputs in turn onto one channel and a demultiplexer, using the same timing, routes each sample to the correct output.

    Key words

    Say what each word means before you turn the card.

    Time slots

    Try answering aloud or in your head before turning the card.

    Multiplexer

    Try answering aloud or in your head before turning the card.

    Demultiplexer

    Try answering aloud or in your head before turning the card.

    Synchronisation

    Try answering aloud or in your head before turning the card.

    See every definition
    Time slots
    Short, repeating slices of time in which each signal is allocated the whole channel.
    Multiplexer
    Samples each input in turn so the channel carries a rapid sequence of samples.
    Demultiplexer
    Uses the same timing at the far end to route each sample to the correct output.
    Synchronisation
    Transmitter and receiver must stay synchronised so that samples are not sent to the wrong destination.

    Label the diagram

    Some boxes have lost their names. Pick the right name for each number.

    The diagram again, with 3 boxes numbered instead of named. A top-down flowchart. Input signals lead to a box for the multiplexer sampling each input in turn, which leads to one communication channel, then to a box describing the rapid sequence of samples: input 1, input 2, input 3, back to input 1. This leads to a box for the demultiplexer using the same timing, which leads to a box for each sample being routed to the correct output. Two separate boxes feed into the chain: one stating that the transmitter and receiver must stay synchronised, with an arrow into the demultiplexer box, and one stating that the sampling rate must be high enough to represent each signal faithfully, with an arrow into the multiplexer box.

    • 1Box 1

    • 2Box 2

    • 3Box 3

    0 of 3 labelled

    There is more to this lesson

    The full lesson goes on to check your understanding and help you earn the marks. Create a free account to carry on, with your progress saved.

    Carry on with the full lesson

    A week of Premium from your first lesson · Then the free plan continues · No card, no charge

    Test your understanding of Time-division multiplexing (A-level only): Basic principles of time-division multiplexing.

    Active recall beats re-reading. Take an instant quiz now to test what you’ve learned and lock it into long-term memory.

    Take topic quiz

    A week of Premium from your first lesson · Then the free plan continues · No card, no charge

    Start free

    Cookies on MasteryMind

    Essential cookies keep you signed in.

    Analytics and advertising cookies stay off unless you accept.

    Read our Privacy Policy.