Chapter 11. Sampling and Pulse Modulation. The Sampling Theorem PAM -- Natural and Flat-Top Sampling Time-Division Multiplexing ( TDM ) Intersymbol Interference ( ISI ) Pulse Width and Pulse Position Modulation Demodulation Digital Modulation Pulse Code Modulation ( PCM )
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Time-Division Multiplexing (TDM)
Intersymbol Interference (ISI)
Pulse Code Modulation (PCM)
Delta Modulation (DM)
Figure 11-1. Impulse sampling of an analog voltage.
consists of instantaneous impulses every nTs sec, where n = 0, +1, +2, …
Figure 11-2. Sample spectra and their outputs. (a) fs > 2fA(max) Nyquist criteria met. (b) fs < 2fA(max) Frequency foldover of “aliasing” distortion occurs. (c) fs > 2fA(max) and recovery of original information with low-pass filter. (d) The original analog signal spectrum following recovery as in (c).
Figure 11-3. Pulse amplitude modulator, natural sampling.
Figure 11-4. Sample-and-hold circuit and
Figure 11-6. Time-division multiplex of three information sources.
fA1(max) = 4 kHz, fA2(max) = 20 kHz,
and fA3(max) = 4 kHz.
the multiplexing must proceed at
f> 2fA(max) = 40 kHz
to satisfy the worst-case condition.
The commutator completes one cycle, called a frame, every 1/40 kHz = 25 ms.
3 pulses/frame x 40k frames/s = 120k pulses/s.
you discover that there are
7 pulses/frame x 8k frames/s = 56k pulses/s, which looks good.
Figure 11-7. Possible TDM solution.
(2 pulses/25ms)/(7 pulses/frame) = 11.428k frames/s
(11.428k frames/s) x (7 pulses/frame) = 80k pulses/s
with no errors.
Figure 11-8. TDM solution for minimum transmission line pulse rate.
Figure 11-11. Analog/pulse modulation signals.
Figure 11-12. Pulse width modulator.
Figure 11-13. Pulse position modulator.
Figure 11-14. PPM demodulator.
Figure 11-15. A 3-bit PCM system showing
Figure 11-19. Possible delta modulation encoder.
Figure 11-20. DM demodulator.
Fig. 11-21. Up-down staircase generator
for delta modulator.
Fig. 11-22. Critical design parameters in constant
step-size linear delta modulation.
The step size must be 10 mV.
that is, to avoid slope overload.
(t = 0 in Figure 11-23).
slope = dv(t)/dt
= (d/dt).(Vsinwt) = wVcoswt.
Figure 11-23. Example problem.
Fig. 11-24. Integrating linear delta modulator
block diagram and signals.
Figure 11-25. Adaptive delta modulator.
Figure 11-26. ADM with step or double step sizes.
Arrows are shown along the horizontal axis to indicate where the step size changes. These changes are based
on the number of 1s and 0s of the previous 4 bits.
Fig. 11-27. Different DM results depending on
step size used.
Figure 11-30. Pulse and digital modulation waveforms.