1. Module 5: Digital Techniques and
Electronic Instrument Systems
5.9 Multiplexing

2. Multiplexing
 Simplex bus:
 Data flow always
in one way.
 Half duplex bus:
 Send and receive
but not in the
same.
 Full duplex bus:
 Send and receive
simultaneously.

3. How can a transmitter send information to more than
one receivers through a single wire?
 Multiplexing
 2 types of multiplexing:
 Frequency Division Multiplexing (FDM):
 The information intended to for different receivers is differentiated by
using different frequencies.
 Time Division Multiplexing (TDM):
 Each transmitter has its own time-slot at which he can send
information.

4. Frequency Division Multiplexing
 Each transmitter
modulates the data
using a “carrier” with a
specific frequency.
 The receiver obtains
the original data using
a filter and a
demodulator circuit,
which removes the
“carrier”.
 ADSL example:
 Voice: 0 – 4KHz
 Upstream: 25 – 138KHz.
 Downstream: 138 – 1104KHz

5. Frequency Division Multiplexing
 Signal in time domain
 Signal in time
frequency domain
 OFDM: Orthogonal
carriers overlap, but
data can be still
recovered by the
receiver.
  Bandwidth savings!

6. Time Division Multiplexing
 Each receiver has a
specific timeslot.
 Multiplexer receives
one bit form each
transmitter in order,
combines them to a
TDM frame and
sends them to the
channel.
 Demultiplexer
receives the TDM
frame and gives
each bit the
appropriate receiver
in order.

7. Multiplexer
 a, b: address lines.
 A, B, C & D:
transmitters.
 Q: Output connected
to the channel.
 a & b define from
which transmitter,
data will be
forwarded to the
output.
 Usually a clock is
connected to a & b to
perform TDM.

8. Demultiplexer
 s0, s1: address
lines.
 DATA: data received
from the channel.
 Y0,…, Y3: receivers.
 s0 & s1 will select to
which of receivers
the data will be
forwarded.
 s0 & s1 are usually
connected to a clock
to perform TDM.

9. Symbols