Concepts of Multiplexing Many input signals to one transmission media

1. Computer Control Engineering Technology, Electrical Engineering Technology, Electronics – Fox Valley Technical College • Concepts of Multiplexing • Many input signals to one transmission media • Reduces the number of channels or conductors running from • point A to point B • Added complexity in the muxing and demuxing control

2. Computer Control Engineering Technology, Electrical Engineering Technology, Electronics – Fox Valley Technical College Frequency Division Multiplexing (FDM) Each input signal uses a unique carrier frequency. The different carrier frequencies are spread across a given frequency spectrum. The FDM signals can then be transmitted via RF or via some physical media.

3. Computer Control Engineering Technology, Electrical Engineering Technology, Electronics – Fox Valley Technical College • Spectrum of a Frequency Division Multiplexing System • Bandwidth is divided into smaller channels • Examples: AM or FM radio, Television, Cable and Satellite TV

4. Computer Control Engineering Technology, Electrical Engineering Technology, Electronics – Fox Valley Technical College • FDM Receiver • Note the use of band pass filters (BPF) to select channels • or bands

5. Computer Control Engineering Technology, Electrical Engineering Technology, Electronics – Fox Valley Technical College FDM Telemetry System Sensors can be in remote locations or spread across the factory floor. The use of RF in this case supports remote data acquisition. Data can be sent many miles using RF.

6. Computer Control Engineering Technology, Electrical Engineering Technology, Electronics – Fox Valley Technical College • FM / FM Telemetry - Receiver • Multiplexed RF signals are filtered through BPF • PLL’s extract original signal

7. Computer Control Engineering Technology, Electrical Engineering Technology, Electronics – Fox Valley Technical College FDM Telephone Multiplexing – City to City for example Each voice channel is allocated 4 Khz. Each channel modulates a unique carrier. The carriers are all multiplexed into a larger group. Supports multiple communication channels through a single media.

8. Computer Control Engineering Technology, Electrical Engineering Technology, Electronics – Fox Valley Technical College • FDM Telephone Group • 4 Khz per channel • 12 channels, 48 Khz bandwidth for the group • Different carrier frequencies for each channel • Multiple carriers in a group

9. Computer Control Engineering Technology, Electrical Engineering Technology, Electronics – Fox Valley Technical College • Telephone Super Group • Multiplexed groups are then multiplexed to form a super group • 5 groups per super group • 48 Khz per group • Used to support long distance communication

10. Computer Control Engineering Technology, Electrical Engineering Technology, Electronics – Fox Valley Technical College Demuxing a Super Group Each group is recovered by a BPF. The recovered group is fed through a LPF. Each channel from the specific group is recovered by a BPF.

11. Computer Control Engineering Technology, Electrical Engineering Technology, Electronics – Fox Valley Technical College • Time Division Multiplexing • Each user / signal is allocated a certain amount of time • Equal time slots per user / signal • Signals can be grouped into frames or sets

12. Computer Control Engineering Technology, Electrical Engineering Technology, Electronics – Fox Valley Technical College • Time Division Signal or Input Selection Concept • One user / signal is routed to the output at a time for a • fixed amount of time

13. Computer Control Engineering Technology, Electrical Engineering Technology, Electronics – Fox Valley Technical College • 4 Channel Time Division Multiplexing Example • Assume there are 4 different analog signals • Each signal must be sampled and sent to a receiving location

14. Computer Control Engineering Technology, Electrical Engineering Technology, Electronics – Fox Valley Technical College • Using Pulse Amplitude Modulation Time Division Multiplexing • Notice that at each time mark a different signal is sampled • The amplitude of the sampled signal is sent in this case, • some other type of modulation scheme could be use • The receiving end must demux the signals and route them to the • appropriate output

15. Computer Control Engineering Technology, Electrical Engineering Technology, Electronics – Fox Valley Technical College TDM Mux Circuit to Produce Pulse Amplitude Modulation

16. Computer Control Engineering Technology, Electrical Engineering Technology, Electronics – Fox Valley Technical College • PAM TDM Timing Graph • A & B select which input • is sampled • The one shot initiates the sample • The gate outputs enable the • sample to be fed through to • the output

17. Computer Control Engineering Technology, Electrical Engineering Technology, Electronics – Fox Valley Technical College • PAM Frame Synchronizing • Notice how the amplitude of the sync pulse exceeds all • other signals • A comparator detects this and synchronizes the receiver

18. Computer Control Engineering Technology, Electrical Engineering Technology, Electronics – Fox Valley Technical College • Analog Input / Pulse Amplitude Modulation – Transmission • Pulse amplitude modulation to FM – amplitude modulates • the transmitted carrier

19. Computer Control Engineering Technology, Electrical Engineering Technology, Electronics – Fox Valley Technical College • Analog Input / Pulse Amplitude Modulation – Transmissions • Pulse amplitude modulation to FM to PM • PAM signal modulates a sub-carrier • The sub-carriers are summed and they modulate the • phase of the carrier

20. Computer Control Engineering Technology, Electrical Engineering Technology, Electronics – Fox Valley Technical College Demuxing PAM signals from PAM/FM and PAM/FM/PM

21. Computer Control Engineering Technology, Electrical Engineering Technology, Electronics – Fox Valley Technical College • Pulse Code Modulation Multiplexing • PCM’s for each input • are muxed • Resultant output bit • stream must be • clocked at a higher • rate than the data • bit rate to support • high throughput • Note the use of a • sync pulse to separate frames

22. Computer Control Engineering Technology, Electrical Engineering Technology, Electronics – Fox Valley Technical College • Telephone System T-1 Frame – Time Division Multiplexing • Used to support 8 bit A/D conversion of analog (voice) data • 24 channels • 1 sync bit • 193 bit total frame • 5.2 micro second word time, 125 micro second frame time

23. Computer Control Engineering Technology, Electrical Engineering Technology, Electronics – Fox Valley Technical College Questions?