AnalogtoDigital Converters

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Analog-to-Digital Converters

• Prepared by
• Mohammed Al-Ghamdi, 259463
• Mohammed Al-Alawi, 269380

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Outline

• Introduction.
• Types of data.
• Analog data.
• Digital data.
• Analog-to-Digital Converter (How it work).
• Sampling.
• Resolution.
• Inside Analog-to-Digital Converter.
• Parallel design (Flash ADC).
• Digital-to-Analog Converter-based design.
• Integrator-based design.
• Sigma-Delta design.
• Pipeline design.
• Applications.
• Internet.
• Audio CD.
• Conclusion.

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Introduction

• 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.

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Types of data

• Analog data (All values on the time and amplitude
  are allowed).
• Digital data (Only a few amplitude levels are
  allowed).

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Analog-to-Digital Converter (How it work)

• 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).

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Analog-to-Digital Converter (How it work)

• 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.

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Inside Analog-to-Digital Converter

• Since Analog-to-Digital converters were invented,
  different designs were made to fabricate them.
  The most five known designs are
• Parallel design (Flash ADC).
• Digital-to-Analog Converter-based design.
• Integrator-based design.
• Sigma-Delta design.
• Pipeline design.

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Parallel design (Flash ADC).

• 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.

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Digital-to-Analog Converter-based design.

• 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.
• 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.

• 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.

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Integrator-based design.

• There are few ways of designing analog-to-digital
  converters using an integrator. We will discuss
  one of them the single-slope ADC.
• 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.

• 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 (2n-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.

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Sigma-Delta design.

• 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.

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Pipeline design.

• 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.

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Applications

• 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...
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Applications

• 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).

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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
  integrator-base design, the sigma-delta design
  and the pipeline design. All of them perform that
  same job but differ in their efficiency (speed
  space storage).