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1.2 Analog Versus Digital
Analog signals: time-varying signals that
can take on any value across a continuous
range of voltage, current, or other metric.

v(t)
0
米制的,
公制的
t
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1.2 Analog Versus Digital
Digital signals: at anytime,only one of two
discrete values, which we call 0 and 1.
( or Low and High, False and True, negated
and asserted, or whatever)

否定
v(t)
肯定
0 1
0
1
1
0
0
1
Ts
t
0
Digital systems must be circuits to process
binary digits – 0s and 1s according to the definition
of digital signals. Are there any benefits?
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1.2 Analog Versus Digital
How to convert analog signals to digital
signals? (A/D Converter)

Analog
signal
0.2V
Coding
v (t)
Signal
+5V
A/D
0 0 0 0 1 0 1 0
vs (t) Sampling
Ref.
Voltage
vq (t)
Quantization
0.2
t
t
t
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1.2 Analog Versus Digital
Examples of Digital Systems:
 Still pictures. JPEG, BMP, GIF

Video recordings. DVD (Digital Versatile Disk),
VCD (Video Compact Disk) , MPEG, AVI


Audio recordings . CD (Compact Disc), WAV
Automobile carburetors. Microprocessor is
embedded. It can 汽化器
determine how to control the
flow of fuel and oxygen to the engine.
The telephone system. Digital COs & PBXs.
Traffic lights. Controllers use microprocessors.

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1.2 Analog Versus Digital
The Reasons that Digital Circuits Over
Analog Ones
 Reproducibility of results
 Ease of design
 Flexibility and functionality
 Programmability
 Speed
 Economy
 Steadily advancing technology

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