Analog to Digital and vice versa

1
Analog to Digital(and vice versa)

• by Leslie Sroka

2
Analog Signals

• An analog signal varies some physical property,
  such as voltage, in proportion to the information
  that we are trying to transmit. Examples of
  analog technology
• photocopiers
• telephones
• audio tapes
• televisions (intensity and color info per scan
  line)
• VCRs (same as TV)
• Analog signals always suffer from degradation.

3
Digital Signals

• With a digital signal, we are using an analog
  signal to transmit numbers , which we convert
  into bits and then transmit the bits.
• A digital signal uses some physical property,
  such as voltage, to transmit a single bit of
  information.
• Suppose we want to transmit the number 6. In
  binary, that number is 110. We first decide that,
  say, "high" means a 1 and "low" means a 0. Thus,
  6 might look like
• The heavy black line is the signal, which rises
  to the maximum to indicate a 1 and falls to the
  minimum to indicate a 0.

4
Degradation and Restoration of Digital Signals

• The analog signals used to transmit bits degrade,
  too. However, and this is the really cool part,
  the degraded signal can be "cleaned up," because
  we know that each bit is either 0 or 1. Thus, the
  previous signal might be degraded to the
  following
• Despite the general erosion of the signal,
• we can still figure out which are the 0s
• and which are the 1s, and restore it to
• This restoration isn't possible with analog
• signals, because with analog there aren't
• just two possibilities. Compare a photocopy
• of a photocopy ... with a copy of a copy of a
• copy of a computer file. The computer files
• are (very probably) perfect copies of the
• original file.
• The actual implementation of digital transmission
  is somewhat more complex than this, but the
  general technique is the same two signals that
  are easily distinguishable even when they are
  degraded.

5
Converting Analog to Digital

• If digital is so much better, can we use digital
  for music and pictures? Of course! To do that, we
  must convert analog to digital, which is done by
  sampling.
• Sampling measures the analog signal at different
  moments in time, recording the physical property
  of the signal (such as voltage) as a number. We
  then transmit the stream of numbers. Here's how
  we might sample the analog signal we saw earlier
• Reading off the vertical scale on the left, we
  would
• transmit the numbers 0, 5, 3, 3, -4, ... (The
  number
• of bits we need to represent these numbers is the
• so-called bit-resoluton. In some sense it is the
• sound equivalent to images' bit-depth.)

6
Converting Analog to Digital (Cont.)

• Taking discrete measurements to get curse length
  of the signal, which is the good point about
  digital. It can take a lot of static before you
  loose a signal in digital.
• 4,3.5,6,-5,-4,-4,5,5.5

7
Converting Digital to Analog

• Of course, at the other end of the process, we
  have to convert back to analog, also called
  "reconstructing" the signal. This is essentially
  done by drawing a curve through the points. In
  the following picture, the reconstructed curve is
  dashed
• In the example, you can see that the first part
• of the curve is fine, but there are some
• mistakes in the later parts.
• The solution to this has two parts
• the vertical axis must be fine enough resolution,
  so that we don't have to round off by too much,
  and
• the horizontal axis must be fine enough,
• so that we sample often enough.
• In the example above, it's clear that we
• didn't sample often enough to get the detail in
• the intervals. If we double it, we get the
  following, which is much better.

8
Converting Digital to Analog (Cont.)

• Since you have discrete samples of the wave
  length, you can draw or get a best fit curve for
  a continuous signal to be analog.
• When you start to get a little static, you start
  loosing signal.

9
What Makes Analog Display

• VGA (Video Graphics Array)
• Light Tubes
• Continuous Color

10
What Makes Analog Cameras

• Uses Continuous Color System
• Uses Film
• Uses Shutters and Mirrors

11
What Makes Analog Audio

• Lower Channels
• Alternating Signals
• Uses Three Outputs

12
What Makes Analog Communication

• Twisted Pair Cables
• Continuous Signal
• Require much less bandwidth, only about 4.5 MHz
  with a 143.2 Mb/s data rate

13
What Makes Digital Display

• Resolution
• Pixels
• Channels
• Chipsets
• Memory
• DVI (Digital Video Input)
• Clarity

14
What Makes Digital Cameras

• Pixels
• JPEG (Joint Photographic Experts Group)
• TIFF (Tagged Image File Format)
• LCD Display View
• Flash Memory Cards
• More Control in Cameras Menu
• Uses Discrete Color System

15
What Makes Digital Audio

• Direct Signal
• Fiber-Optic or Coax Cables
• Higher Channels
• Uses One Output (Digital Out)

16
What Makes Digital Communication

• Direct or Discrete Signals
• Fiber-Optic
• High Frequency
• LAN (Local Area Network)
• WAN (Wide Area Network)
• DSL (Digital Subscriber Line)
• Digital video transmission standards require as
  much as 74.25 MHz with a data rate of 1485 Mb/s.
  Advances in single-mode optical fiber make these
  higher rates more accessible for longer distances
• Corrects Errors

17
Source Information

• http//puma.wellesley.edu/cs110/lectures/M07-anal
  og-and-digital/
• http//www.mala.bc.ca/lizhk/media113/analog.htm
• http//www.infoplease.com/ce6/sci/A0815509.html
• http//www.fiber-optics.info/articles/analog-v-dig
  ital.htm