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144<br />

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

Output<br />

voltage<br />

8<br />

6<br />

4<br />

M = 8<br />

–2<br />

2<br />

0<br />

–8 –6 –4<br />

–2<br />

2 4 6 8<br />

Input voltage = x<br />

–V = –8<br />

–4<br />

–6<br />

V = 8<br />

–8<br />

(a) Quantizer Output-Input Characteristics<br />

Sampling times<br />

T s<br />

8<br />

6<br />

4<br />

2<br />

Analog signal, a(t)<br />

PAM signal, t = T s<br />

Quantized PAM signal<br />

–2<br />

–4<br />

–6<br />

–8<br />

t<br />

(b) Analog Signal, Flat-top PAM Signal, and Quantized PAM Signal<br />

2<br />

1<br />

–1<br />

–2<br />

Difference between analog signal<br />

and quantized PAM signal<br />

t<br />

(c) Error Signal<br />

PCM word<br />

1 111101101101 1011111110110110110110000000101101101101<br />

0<br />

(d) PCM Signal<br />

t<br />

Figure 3–8<br />

Illustration of waveforms in a PCM system.

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