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138<br />

Baseband Pulse and Digital Signaling Chap. 3<br />

w(t)<br />

0<br />

t<br />

(a) Baseband Analog Waveform<br />

0<br />

t<br />

(b) Impulse Train Sampling Waveform<br />

w s (t)<br />

t<br />

t<br />

0<br />

T s<br />

(c) Resulting PAM Signal (flat-top sampling, d = /T s = 1/3)<br />

Figure 3–5<br />

PAM signal with flat-top sampling.<br />

DEFINITION. If w(t) is an analog waveform bandlimited to B hertz, the instantaneous<br />

sampled PAM signal is given by<br />

w s (t) =<br />

q<br />

a w(kT s ) h (t - kT s )<br />

(3–8)<br />

k =-q<br />

where h(t) denotes the sampling-pulse shape and, for flat-top sampling, the pulse shape is<br />

h(t) = ßa t |t| 6 t/2<br />

b = e1,<br />

t 0, |t| 7 t/2<br />

(3–9)

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