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Sec. 3–9 Time-Division Multiplexing 211
Digital input signals
1
1 0 1 1
Channel 1
1
2 3 4 5 6 7 8 9 10
t
Timedivision
Multiplexer
Output
1
0 0 1 0
Channel 2
1
2 3 4 5 6 7 8 9 10
t
Output TDM signal
1 1 1 0 * 0 0 1 1 0
Input channel
number
* = stuffed bit
1
1
2 3 4 5 6 7 8 9 10
t
2 1 2 1 2 1 2 1 2
Figure 3–38
Two-channel bit-interleaved TDM with pulse stuffing.
applications the clock rates of the input data streams are not related by a rational number. In
these cases, the TDM output signal will have to be clocked at an increased rate above the
nominal value to accommodate those inputs that are not synchronous. When a new input bit
is not available at the multiplexer clocking time (due to nonsynchronization), stuff bits,
which are dummy bits, are inserted in the TDM output data stream. This strategy is illustrated
by the bit-interleaved multiplexer shown in Fig. 3–38. The stuff bits may be binary
1’s, 0’s, or some alternating pattern, depending on the choice of the system designer. The
third TDM type consists of those that operate with asynchronous sources and produce a
high-speed asynchronous output (no stuff bits required) or high-speed synchronous output
(stuff bits required).
Example 3–17 DESIGN OF A TIME-DIVISION MULTIPLEXER
Design a time-division multiplexer that will accommodate 11 sources. Assume that the sources
have the following specifications:
Source 1. Analog, 2-kHz bandwidth.
Source 2. Analog, 4-kHz bandwidth.
Source 3. Analog, 2-kHz bandwidth.
Sources 4–11. Digital, synchronous at 7,200 bitss.