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Digital Technology of Communications; part 1 opt. F

Basics Digital Technology part of IB Communications for both SL and HL

Keith Herold

on 11 March 2015

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Transcript of Digital Technology of Communications; part 1 opt. F

Digital Technology of
-Option F-
IB Curriculum

Our society is addicted and dependent upon communication.
Signal sounds must be different and modified to make communication of information possible...
*You wouldn't understand any conveyance of information if it all sounds exactly the same.
Saying a vowel, e.g., like C
at different intensities (loud and soft) make the vowel sound different.
==Modulation is transmitting information by modifying the signal in some way through an electrical means.
Types of Signals:
signal wave
: contains the info being transmitted.
---the TV show, the radio program, the song you listen to, the text message you read.{tip: signal /see it: the information you see, "the information wave"
carrier wave
: is the means the signal is transmitted such as by radiowave, microwave(cell phones use this), visible light, alternating current of electricity.
{tip: how is it carried, the wave it is carried on...micro, radiowave etc...}
Speed, distance, quality, security, mobility, and cost.
-->these are all very important to us in communications.
Now remember that waves can be depicted as sinusoidal oscillations with variations in amplitude, wavelengths, frequencies, periods.
each signal transmitted by the carrier wave has a power spectrum generally associated with voltage variations, thus changing the amplitude (which is maximum displacement) and thus changing the signals identification markers.
*the displacement in the sinusoidal wave is directly related to the voltage (in cases of communication signals). This is displayed as a "Y"-axis change and can be thought of as a power change as well as amplitude. (AM carrier signals vary amplitude whereas FM varies frequency and thus called freq.modulation
Since we are all part of the digital revolution, communications are a part of our life. Whether we use satellites to bounce off electromagnetic waves like microwaves or radio waves, whether we send signals inside of optic fibers or use cables.....
this is physics!
At this point it makes more sense to discuss the digital technology of communications.
Please note:
In Tsokos it is topic 8 in Dickinson topic 14.1 &14.2
Option F is communications and SL is F1-F4
HL is F1-F6
Both HL and SL include digital technology with in the communications option.
Digital Tech. includes information about compact discs, DVD (digital versatile discs), CCD's (charged-coupled devices. All to create digital images and sounds. How does the internet work?
How many of these do you use everyday??
First every student needs to get a grasp on differences between analogue and digital signals.
digital has discrete steps between values and no in between.
whereas analogue has infinite level between values possible.
so digital is quantized and analogue is not...
an example might be: an alcohol or mercury thermometer vs. a digital thermometer.
Microprocessors in devices control the outcome by interpreting the signals. In communications of computers for example we use a binary system. It is either on or off (a true digital system)
Binary means there are two values only. 1 or 0
These values are each called a bit. Eight bits together=a byte of information.
When a switch is on, the microprocessor interprets this as a 1. When the switch is closed, the processor calls it a 0.
These binary values in combinations can be turned into a decimal system of values.
A binary code is made of these "on or off signals". Computers commonly use a base 2 system. But the most common system we use today is a base 10 system. .
e.g.: the number 3741 can be represented by: (3E3)+(7E2)+(4E1)+(1E0)
Binary code is a base 2 system and uses only 1 and 0. *remember one digit is a bit of memory on a storage device. Now let us look at a binary conversion table.
lets analyze how we get this binary code... in the next frame. Be patient as it is rather difficult at first to grasp!
The hexadecimal system is associated more with computing with a base of 16. Digits of 0-9 and the letter A-F. 8 bit numbers are used to represent basic word processing characters as in Notepad (in *Windows). Computer memory is measured in:
kilobytes, megabytes, gigabytes, terabytes generally.
How many different #'s can be represented by a byte? 2 bytes? *remember 8 bits =byte
a. 256 2^8=256
b. probability of A x prob. of B= A x B=
256 x 256= 65,536
A digital signal is a coded form of a signal that takes the discrete values of 0 or 1 only. Analogue signals are continuous signals.
If we take a analogue signal and sample it in time intervals we will get a reading of various changes.
Now take that concept and we can convert analogue data into digital binary data.
Tsokos states typically for audio signals a rate of 8000 times or samples per second or 1/8000 = 125microseconds. This will result in a pulse modulated signal. In between the sampling there will be some information loss...
The volume changes can be thought of as voltage fluctuations. PAM method/or signal refers to a pulse amplitude modulated signal. Associated with Analogue sampling to convert to digital
The advantage of an analogue signal:
accurate representation of the source of the signal.
background noise is picked up.
often corruption in the transmission
not as convenient to store lot of information on an LP (vinyl plastic record)
Digital advantage:
No background noise
easier transmission of signal
some information loss since it is not continuous.
Another method of past importance and use was the Tape Cassette: this worked by magnetic variations on a special tape. The cassette player has a head the tape goes back and it interprets the variations as volume and pitch.
CD's and DVD's have bumps and pits. Length of pits and bumps are precise arranged around the disc in a circular fashion. A Laser Light shines on this track. the depth of the pits is 1/4 lambda (wavelength). You must memorize this. The light is reflected to a photo-diode. The signal from constructive and destructive interferences are read and interpreted(a series of 1's and 0's are produced). The digital interpretation is now converted to analogue signals.
One bit of data is produced by a bump/pit pair on a DVD or CD. Remember a byte is 8 bits.
*you should know how to calculate the storage capacity of a CD/DVD given some information.
Discuss the advantages/disadvantages of digital vs. analogue storage.
Too long to put here so look at page 363 Dickinson but I will discuss this with you in class. Also see p. 385 (in option C) for moral, ethical, social, economic and environmental implication of society having ever increasing capacity of digital tech like cell phones. This is a concept of both SL and HL.
CAPACITORS: I believe we have covered much of this already. A small review is in order though....
Capacitors store electrical charge
consists of parallel conductive materials and separated by a dielectric(non-conductor)
help store binary memory in computers with power losses
Capacitance=measure of the amt. of Electric charge stored per unit of potential difference
units ==>farads 1uF=10^-6 F
CCD=charged coupled device
made of millions of tiny metal oxide capacitors in an array.
utilizes the photoelectric effect, whereby light causes electrons to flow and they are stored in this capacitor.
more intense light=>to higher charges on each pixel.
Each pixel assigned a digital number.
Short for charge-coupled device, an instrument whose semiconductors are connected so that the output of one serves as the input of the next. Digital cameras, video cameras, and optical scanners all use CCD arrays.
the measure of sensitivity of the pixel: It can be defined as the ratio of the number of photo-electrons emitted from the surface of the pixel to number of incident photons.
QE= N(emitted electrons)/N(incident photons)
Concept of Magnification:
ratio of size of image to size of object
this increases the pixels being exposed and could enhance the quality of detail.
Be able to state: two points on an object may be resolved on a CCD if the images of the points are at least two pixels apart....
Camera's have Megapixels, the more the better quality of the photo.
better resolution or amount of detail...
Realize the applications of CCD in digital camera's, video recorders, and scanners. Read Dickinson on the points of each page 366.
The communication main section will be a separate PREZI called communications.
What is an HDD?
Of course images of objects we will photograph are large but the digitized image is small.
So what is the height of the image compared to height of the
The PAM system: pulse
amplitude modulated signal
making words out of binary.
American Standard Code for International Interchange.
A thin slice of silicon with many small squares that act as capacitors. Each, when hit my light, stores an electrical charge. The silicon has an impurity added. A photodiode of the CCD. Each pixil, if charged, emits a signal that is binary and records the image...
Capacitance "C"=Q/v
Charge/p.d or voltage.
**charge in Coulombs.
Final image quality is determined by a combination of:
1. magnification
2. size of the CCD
3. quantum efficiency {ratio of the electrons freed by the photoelectric effect to the amount of photons striking the pixil on the CCD.
A color filter is placed over the pixils on the CCD with primary colors of: r,b,g red, blue, and green. This makes it possible to digitize color by the absorption of the image and the reflected wavelengths sent to the CCD.
This CCD tech. has been replacing the need for X-ray film. In Astronomy the lens is now attached to a digital camera with CCD application.
Nyquist frequency/theory:
States that to record a certain frequency of a signal properly,
the sampling rate must be at least twice the frequency.
nb: waves have crest and troughs or nodes and antinodes.....
e.g. Human can only hear up to 20K Hz. So the sampling rate should be around 40k Hz to
get both the crest and the trough of the wave.
YOU Must now go to the PREZI on Communications
analogue to digital conversion
a very small sampling time (quantum level)
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