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 Computer Control Engineering Technology, Electrical Engineering Technology, Electronics – Fox Valley Technical College

Frequency Division Multiplexing (FDM) Computer Control Engineering Technology, Electrical Engineering Technology, Electronics – Fox Valley Technical College 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.

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

FDM Telemetry System Computer Control Engineering Technology, Electrical Engineering Technology, Electronics – Fox Valley Technical College 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.

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

FDM Telephone Multiplexing – City to City for example Computer Control Engineering Technology, Electrical Engineering Technology, Electronics – Fox Valley Technical College 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.

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 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 Computer Control Engineering Technology, Electrical Engineering Technology, Electronics – Fox Valley Technical College

Demuxing a Super Group Computer Control Engineering Technology, Electrical Engineering Technology, Electronics – Fox Valley Technical College 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.

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 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 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 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 Computer Control Engineering Technology, Electrical Engineering Technology, Electronics – Fox Valley Technical College

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

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

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