The document discusses analog to digital converters (ADCs). It describes successive approximation ADCs which convert continuous analog signals to discrete digital representations through binary search. It also discusses flash ADCs, oversampling to achieve processing gain, sigma-delta converters, and provides examples of terminology used in ADCs like reference voltages.

1. Unit 2 Electronic Circuits
Lesson 6 Analog to Digital Converters

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Lesson 6 Analog to Digital Converters
• Backgrounds
• Text tour
• Language in use
– Vocabulary

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• Terminology
– Successive approximation
Backgrounds

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A successive approximation ADC is a type of analog-to-digital
converter that converts a continuous analog waveform into a discrete
digital representation via a binary search through all possible
quantization levels before finally converging upon a digital output
for each conversion.
Successive Approximation

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Text tour
• Outline
– Flash ADC
– Over-sampling to Achieve Processing Gain
– Sigma-Delta Converters
– Summary

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• A popular and readily understood type of ADC
– very high-speed conversion
– can accommodate high sampling rates
– much power dissipation
• The flash converter operates by …
– 2N–1 comparators
– For large numbers of bits (N) (e.g. >14 bits), …
• The output spectrum of a typical flash
converter…
Flash ADC
 
6.02 1.76
SNR N dB
 

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Figure 2.5 Flash ADC Block Diagram
Flash ADC

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Figure 2.6 FFT of Typical ADC Samples
Flash ADC

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• Oversampling is the process of sampling a signal
with a sampling frequency significantly higher
than the Nyquist rate.
• A simple formula for the maximum processing
gain
Processing gain (dB) = 10 log (sample rate/ 2 × signal
bandwidth).
• Examples
– PC sound cards
– GSM
Over-sampling to Achieve
Processing Gain

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Figure 2.7 Over-Sampling and Quantization Noise
Over-sampling to Achieve
Processing Gain

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• A block diagram of a basic sigma–delta converter
– essentially a highly over-sampling 1-bit ADC (the
comparator) followed by digital filtering and
decimation
• The comparator, just like in the analog version, decides whether its
input value is higher or lower than a certain threshold and puts out a
single bit signal, the bitstream (a sequence of bits).
• A 1-Bit DAC can provide output two different values only. They are
termed VRef- and VRef+. Examples:
Sigma-Delta Converters

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Figure 2.8 Basic Sigma–Delta Converter
Sigma-Delta Converters

14. • In the analogue modulator input ranges
result out of the reference voltages as
follows:
VRef- VRef+
• 0 V +1 V
0V to +1 V (Input Range)
• -10 V +10 V
-10 V to +10 V (Input Range)
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Figure 2.9 Quantization Noise Shaping in Sigma-Delta Converters
Sigma-Delta Converters

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• In fact, there are many tens of ADC methods in use,
Successive Approximation, Multipass, Interpolating,
Subranging, Bit-Per-Stage to name but a few of the flavors,
each potentially having some benefit in performance over
its rivals.
• Careful study of the performance specifications on the data
sheet will determine the best choice for your application.
Summary

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• Vocabulary
– reference, solution, respectable, interpolate,
notion
Language in use

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Vocabulary

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Reference in dictionary
• To supply references to
• To mention in a reference; refer to:
– He referenced her book in his speech.

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Reference in text
• The flash converter operates by simultaneously presenting
the input signal to a bank of 2N–1 comparators, whose
reference voltages are set by a resistor chain to exactly
correspond to all of the possible sample levels, which can
be represented by the converter

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• backward reference
• baseline reference
• black-level reference
• luminance reference
• page reference
• phase reference
• speed reference
Reference in use

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Solution in dictionary
• A homogeneous mixture of two or more substances, which may be
solids, liquids, gases, or a combination of these.
• The process of forming such a mixture.
• The state of being dissolved.
• The method or process of solving a problem.
• The answer to or disposition of a problem.

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Solution in text
• For large numbers of bits (e.g. >14 bits), the number of
resistors needed (2N–1) becomes prohibitively large for
most practical applications. Also, the power consumption
is considerably higher than some of the slightly slower and
more exotic solutions.

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Solution in use
• adequate solution
• algebraic solution
• alternative solution
• arithmetical solution
• battery solution
• best solution
• characteristic solution
• engineering solution
• glue solution
• tabulated solution

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Respectable in dictionary
• Meriting respect or esteem; worthy.
• Of or appropriate to good or proper behavior or conventional conduct.
• Of moderately good quality:
• Considerable in amount, number, or size:
• Acceptable in appearance; presentable:

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Respectable in text
• The processing gain possible is thus: processing gain (dB)
= 10 log (80 000 000/2 × 200 000) = 26 dB，resulting in
a very respectable 74 + 26 = 100 dB SNR for the sampled
GSM signal.

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Interpolate in dictionary
• To estimate a value of (a function or series) between two
known values.

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Interpolate in text
• In fact, there are many tens of ADC methods in use,
Successive Approximation, Multipass, Interpolating,
Subranging, Bit-Per-Stage, to name but a few of the
flavors, each potentially having some benefit in
performance over its rivals.

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Notion in dictionary
• A belief or opinion.
• A mental image or representation; an idea or conception.
• A fanciful impulse; a whim.

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Notion in text
• This concept of processing gain leads us nicely into the topic of
sigma–delta converters. These take the notion of processing gain to the
extreme to achieve very high performance, low cost, low power
devices ideally suited for audio applications, with simple analog
interfacing (little or no anti-aliasing filters).

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Notion in use
idea thought notion concept conception
These nouns refer to what is formed or represented in the
mind as the product of mental activity.
• Idea has the widest range:
– Fruit is not her idea of a dessert.
– Don't get any ideas about revenge.
– Human history is in essence a history of ideas（H.G. Wells).

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Notion in use
idea thought notion concept conception
• Thought is applied to what is distinctively intellectual
and thus especially to what is produced by contemplation
and reasoning as distinguished from mere perceiving,
feeling, or willing:
– Quiet! She's trying to collect her thoughts.
– I have no thought of going to Europe.
– Language is the dress of thought. (Samuel Johnson).

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