Transcript Analog-to-Digital Converters

Analog-to-Digital
Converters
Prepared by:
Mohammed Al-Ghamdi, 259463
Mohammed Al-Alawi, 269380
Outline
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Introduction.
Types of data.
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Analog-to-Digital Converter (How it work).
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Parallel design (Flash ADC).
Digital-to-Analog Converter-based design.
Integrator-based design.
Sigma-Delta design.
Pipeline design.
Applications.
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Sampling.
Resolution.
Inside Analog-to-Digital Converter.
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Analog data.
Digital data.
Internet.
Audio CD.
Conclusion.
Introduction
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Most of the data in our life are analog.
In computers, all what can be stored and dealt
with are digital data.
The solution was analog-to-digital converters.
Types of data
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Analog data (All values on the time and amplitude are allowed).
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Digital data (Only a few amplitude levels are allowed).
Analog-to-Digital Converter (How it work)
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Sampling.
What the ADC circuit does is to take samples from the
analog signal from time to time. Each sample will be converted
into a number, based on its voltage level (as in the figure).
Analog-to-Digital Converter (How it work)
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Resolution.
What the ADC does is to divide the “y” axis in “n” possible
parts between the maximum and the minimum values of the
original analog signal, and this “n” is given by the variable size. If
the variable size is too small, what will happen is that two
sampling points close to each other will have the same digital
representation, thus not corresponding exactly to the original
value found on the original analog signal, making the analog
waveform available at the DAC output to not have the best
quality.
Inside Analog-to-Digital Converter
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Since Analog-to-Digital converters were invented, different
designs were made to fabricate them. The most five known
designs are:
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Parallel design (Flash ADC).
Digital-to-Analog Converter-based design.
Integrator-based design.
Sigma-Delta design.
Pipeline design.
Parallel design (Flash ADC).
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It works by comparing the
input voltage of the analog
signal to a reference voltage,
which would be the maximum
value achieved by the analog
signal. For example, if the
reference voltage is of 5 volts,
this means that the peak of
the analog signal would be 5
volts. On an 8-bit ADC when
the input signal reached 5
volts we would find a 255
(11111111) value on the ADC
output, i.e. the maximum
possible value.
Digital-to-Analog Converter-based design.
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There are few ways to design an analog-to-digital Converters using a DAC
as part of its circuit. We will present one of them: the ramp counter.
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Vin is the analog input and Dn thru D0 are the digital outputs. The control
line found on the counter turns on the counter when it is low and stops the
counter when it is high.
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The basic idea is to increase
the counter until the value
found on the counter matches
the value of the analog signal.
When this condition is met,
the value on the counter is the
digital equivalent of the
analog signal.
Integrator-based design.
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There are few ways of designing analog-to-digital converters using an
integrator. We will discuss one of them: the single-slope ADC.
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We can see a single-slope ADC in the figure. We can notes that it is very
similar to a ramp counter ADC, as it uses a counter, but instead of using a
DAC, it uses a circuit called integrator, which is basically formed by a
capacitor, a resistor and an operational amplifier. The MOSFET transistor
makes the necessary control circuit.
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The integrator produces a sawtooth
waveform on its output, from zero to the
maximum possible analog voltage to be
sampled, set by -Vref. The minute the
waveform is started, the counter starts
counting from 0 to (2^n-1). When the
voltage found at Vin is equal to the
voltage achieved by the triangle
waveform generated by the integrator,
the control circuit captures the last value
produced by the counter, which will be
the digital correspondent of the analog
sample being converted.
Sigma-Delta design.
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The sigma-delta ADC – also called delta-sigma – uses a different
approach. We can divide it into two major blocks: analog modulator, which
takes the analog signal and converts it into a stream of bits, and digital
filter, which converts the serial stream from the modulator into a “usable”
digital number.
Pipeline design.
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Pipeline ADC uses two or more steps. First, a coarse conversion is done. In
a second step, the difference to the input signal is determined with a digital
to analog converter (DAC). This difference is then converted finer, and the
results are combined in a last step. This type of ADC is fast, has a high
resolution and only requires a small die size.
Applications
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Internet.
Internet network are connected using telephone networks, which
carry analog signals only. For that reason, a modem is required to
convert the digital data in the computers into analog signals that can
travel within the telephone network. Then reconverted in the destination
into its original form (digital data). This modem is considered to be an
ADC as a DAC.
1101...
1101...
Applications
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Audio CD.
We know that music is actually sound waves (analog). So, to store
these analog data in a CD, we have to first convert them into digital
storable data. Therefore, ADCs are used. In case of audio CD, a high
sampling rate is used (44,100 Hz) to achieve a good sound resolution.
So, when we play the audio CD, an inverse proceed is done. A DAC is
used to reconvert the digital data stored in the CD back to its original
format (analog data).
Conclusion.
In conclusion, we can see that ADCs play a major role in
Computers Communications. The Internet network itself depends on
the process of ADCs. Moreover, we saw how the process of ADC is
done. In addition to that, we saw that there are many designs for
ADCs. The most five known designs are the parallel design (flash
ADC), the digital-to-analog converter-based design, the integratorbase design, the sigma-delta design and the pipeline design. All of
them perform that same job but differ in their efficiency (speed &
space storage).