6. Quantization level (step)
• Quantization is the process of converting a continuous
range of values into a finite range of discreet values. This
is a function of analog-to-digital converters, which create a
series of digital values to represent the original analog
signal.
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The simplest way to quantize a signal is to choose the
digital amplitude value closest to the original analog
amplitude.
7. Sample and hold circuit
• In electronics, a sample and hold (S/H, also "follow-and-
hold") circuit is an analog device that samples (captures,
grabs) the voltage of a continuously varying analog signal
and holds (locks, freezes) its value at a constant level for a
specified minimum period of time.
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8. Zero order hold
• The zero-order hold (ZOH) is a mathematical model of
the practical signal reconstruction done by a conventional
digital-to-analog converter (DAC).
• It describes the effect of converting a discrete-time signal
to a continuous-time signal by holding each sample value
for one sample interval.
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9. Acquisition time
• This term relates to sampling A/Ds which utilize a
track/hold amplifier on the input to acquire and hold the
analog input signal.
• Acquisition time is the time required by the T/H amplifier
to settle to its final value after it is placed in the track
module.
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10. Dynamic range
• Dynamic range, abbreviated DR or DNR, is the ratio
between the largest and smallest values of a changeable
quantity, such as in signals like sound and light.
• Dynamic range is the difference between the smallest and
largest usable signal through a transmission or processing
chain or storage medium.
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11. Signal-to-noise ratio
• Signal-to-noise ratio (abbreviated SNR or S/N) is a
measure used to compares the level of a desired signal to
the level of background noise.
• A ratio higher than 1:1 (greater than 0 dB) indicates more
signal than noise.
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12. Digitization
• Digitization, less commonly digitalization, is the process
of converting information into a digital (i.e. computer-
readable) format, in which the information is organized
into bits.
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13. Nyquist theorem
• The highest frequency component in an analog signal
determines the bandwidth of that signal. The higher the
frequency, the greater the bandwidth, if all other factors
are held constant.
• Suppose the highest frequency component, in hertz, for a
given analog signal is fmax. According to the Nyquist
Theorem, the sampling rate must be at least 2fmax or twice
the highest analog frequency component.
• The number of samples per second is called the sampling
rate or sampling frequency.
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14. Aliasing
• Aliasing is an effect that causes different signals to
become indistinguishable (or aliases of one another) when
sampled. It also refers to the distortion or artifact that
results when the signal reconstructed from samples is
different from the original continuous signal.
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Left: An aliased image
of the letter A in Times
New Roman.
Right: An anti-aliased
image.
15. Anti-aliasing filter
• An anti-aliasing filter (AAF) is a filter used before a signal
sampler to restrict the bandwidth of a signal to
approximately or completely satisfy the sampling theorem
over the band of interest.
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16. 25/8/19 16
Text tour
• Outline
– Introduction
– The Essentials of Analog-to-digital and Digital-to-
analog Conversion
– Technologies for digital signal processing
• The FPGA Alternative
• The ASIC Alternative
• The GPP Alternative
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Introduction
• We don't speak in a digital signal. A digital signal is a
language of 1s and 0s that can be processed by
mathematics. We speak in real-world, analog signals.
Analog signals are real world signals that we experience
everyday - sound, light, temperature and pressure. A digital
signal is a numerical representation of the analog signal. It
may be easier and more cost effective to process these
signals in the digital world.
• In the real world, we can convert these signals into digital
signals through the analog-to-digital converter, process the
signals and if needed, bring the signals back out to the
analog world through the digital-to-analog converter.
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The Essentials of A/D and D/A
Conversion(1) A/D Conversion
Figure 6.1 The analog-to-digital conversion
To summarize, A/D comprises anti-aliasing, sampling,
quantization and digitisation.
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The Essentials of A/D and D/A
Conversion(2) D/A Conversion
Figure 6.2 The digital-to-analog conversion
Anti-imaging filter: A reconstruction filter is used to construct a smooth
analog signal from a digital input, as in the case of a digital to analog
converter (DAC) or other sampled data output device.
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• Advantages of designing with DSPs over other
microprocessors:
– Single-cycle multiply-accumulate operations (MAC)
– Real-time performance, simulation and emulation
– Flexibility
– Reliability
– Increased system performance
– Reduced system cost
Technologies for DSP
DSPs
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• Have the capability of being reconfigurable within a
system
• Offer greater raw performance per specific operation
because of the resulting dedicated logic circuit.
Technologies for DSP
FPGAs
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• Can be tailored to perform specific functions extremely
well
• Can be made quite power efficient.
• Cannot be iteratively changed or updated while in product
development.
Technologies for DSP
ASICs
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• Best suited for performing a broad array of tasks.
• For applications in which the end product must process
answers in real time or must do so while powered by
consumer batteries, GPPs comparatively poor real time
performance and high power consumption all but rules
them out (not considerable).
Technologies for DSP
GPPs (General-Purpose Processors)
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Reciprocal in dictionary
• Interchangeable; complementary:
– reciprocal electric outlets.
• Of or relating to the reciprocal of a quantity.
• A number related to another in such a way that when
multiplied together their product is 1.
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Reciprocal in text
• The length of the sampling interval is the same as the
sampling period, and the reciprocal of the sampling
period is the sampling frequency fs.
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Precede in dictionary
• To come, exist or occur before in time.
• To come before in order or rank; surpass or outrank.
• To be in a position in front of; go in advance of.
• To preface; introduce ：
– He preceded his lecture with a humorous anecdote.
• To come or go before in time, order, rank, or position.
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Precede in text
• To make sure aliasing will not occur, sampling is always
preceded by low pass filtering.
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Deduce in dictionary
• To reach (a conclusion) by reasoning.
• To infer from a general principle; reason deductively.
• To trace the origin or derivation of.
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Deduce in text
• All of the important signal characteristics can be deduced
from the copy of the spectrum that appears in the
baseband through sampling.
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• Characterized by or involving repetition, recurrence,
reiteration, or repetitiousness.
• Iteration ： In computer programming, a process which
repeats the same series of processing steps until a
predetermined state or branch condition is reached
Iterative in dictionary
33. 25/8/19 33
• However, since ASICS are not field-programmable, their
functionality cannot be iteratively changed or updated
while in product development.
Iterative in text
34. 25/8/19 34
• A hindrance or obstruction in doing something.
**hindrance: A thing that provides resistance, delay or obstruction to
something or someone.
– a speech impediment.
– a defect in a person's speech, such as a lisp or stammer
(repeat ).
Impediment in dictionary
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• As such, every new version of the product requires a
redesign and trips through the foundry, an expensive
proposition and an impediment to rapid time-to- market.
Impediment in text
