8 CHAPTER 1 INTRODUCTION TO DIGITAL SIGNAL PROCESSING
recording and reproduction, have become digital. The wireless communications
industry are replacing analog components in radios, as well as back - end audio and
signal decoding sections, with digital devices. Images and video signals are now
routinely coded and decoded as digital signals. Discrete - time systems, as defi ned,
are rarely found in use today except as part of the sampling subsystems (samplers)
found in ADCs. The reason for this paradigm shift from analog signal processing to
DSP is primarily due to two breakthroughs. The fi rst is the sampling theorem and
the second is the product of the fruitful digital semiconductor industry. Once this
bridge was crossed, it became logical to replace everything possible with digital
technology.
DSP : A DISCIPLINE
Signal processing is a gift of the sampling theorem and formidable armada of com-
panion theories, methodologies, and tools, such as the celebrated FFT. Initially DSP
was envisioned simply as an analog replacement technology. It is now clearly appar-
ent to many that DSP will move into new areas and become the dominant signal
processing technology in the 21st century. DSP has matured to the point where it
can claim to be an academic discipline replete with a rich infrastructure industry.
DSP continues to gain semiconductor market share mainly because it can deliver
solutions. The DSP advantage is summarized below.
Digital Advantages
The attributes of a digital solution are as follows:
• Both analog and digital systems can generally be fabricated as highly
integrated semiconductor systems. Compared with analog circuitry, digital
devices can take full advantage of submicron technologies and are generally
more electronically dense, resulting in both economic and performance
advantages.
• As semiconductor technologies shrink (deep submicron) and signal voltages
continue to decline (1.25 V and lower), the intrinsic signal - to - noise ratio found
at the transistor level decreases. Digital systems are far more tolerant of such
internal noise. These devices, however, are essentially useless as an analog
system (e.g., equivalent 3 - bit precision per transistor).
• Digital systems can operate at extremely low frequencies, which would require
unrealistically large capacitor and resistor values if implemented as an analog
solution.
• Digital systems can be designed with increased precision with only an incre-
mental increase in cost, whereas the precision of an analog system precision
is physically limited (10 bits ∼ 60 - dB dynamic range typical).
• Digital systems can be easily programmed to change their function whereas
reprogramming analog systems is extremely diffi cult.