Digital Technology Topic 14
Solving Binary numbers:
Expressing the decimal number 35 as a binary number:
25 + 0 + 0 + 0 + 21 + 20 = 35 which means that the number 35 in binary can be expressed as
100011.
Note: the easiest way to do these is to go from 2𝑛 to 20 , n being the biggest number which is bellow
the number you are trying to solve. In the example up there the biggest number bellow 35 was 32
(25 ). Then if you use the value then it’s a 1, if you don’t then it’s a zero.
If you want to express a six bit number 100011 into decimal you just go the opposite way.
25 + 24 + 23 + 22 + 21 + 20 =
1
0
0
0
1
1
This means if you have a one you take the value, but if you have a zero you do not.
Different storages in Analogue and Digital form:
Analogue can be defined as “signals which are continuous, varying between two extreme values in a
way that is proportional to the physical mechanism that creates the signal.” (Tsokos)
This means that the signal flows, there are no bumps in as you can see in the picture bellow.
Digital signal “is a coded form of a signal that takes discrete values 0 or 1 only.” (Tsokos)
Where as this one if there is a 1 there is voltage and if there is a zero the voltage is zero as well. You
can see this in the picture below.
http://www.privateline.com/manual/fig3_1.gif
CD’s:
The first thing which is done when a CD is being written or data is being stored on the CD is that the
Analogue Signal is being converted to Digital. After it is converted to Digital the sequence or (0 and
1) are being in printed on the CD. The way this is done is that small marks are made on the CD. These
marks are called pits. But since if the whole CD was covered in pits then there would be no marking
so the space left between the pits are called lands. The pits are 500nm wide and can be from 830 nm
to 3560 nm long. Of course when the disk is written there is protective layer placed on top and then
a laser reads it when you up it in a CD player.
𝜆
We can calculate the depth of the pit with the equation 𝑑 = 4. 𝜆 being the wavelength of the laser
reading the CD.
DVD’s are similar to CD but they have a lot more space on them. Material can be written on both
sides of the DVD or it can have two layers, one on top of the other.
http://referate.mezdata.de/sj2003/cd_thomas-ley/res-eigene/pits.jpg
The advantages of Digital Storage:





You have a huge capacity for storing your data in a digital device.
You can access one area of the data very quickly.
You can retrieve it quite fast and it is quite reliable.
It can be encrypted, erased and copied very quickly.
It is easy to transport.
14.2
Capacitance may be defined as “the charge per unit potential difference that can accumulate on a
conductor. Measured in farad (F).”
Charged-coupe device:
Is a device which provides astronomers high resolution images of the other planets, stars, and etc. It
also lets them manipulate and process those images. The device is a silicon chip which measures to
be 20mm x 20mm to 60mm x 60mm. Imagining with CCD is only possible because “the number of
electrons released when light is incident on a pixel is proportional to the lights intensity. The charge
and the potential difference across a pixel is proportional to the intensity of light on the pixel it’s
self.” (Tsokos)
How a CCD works
When the surface of the CCD has been exposed to the light for quite some time, then the voltage
starts build up in the pixels. After the CCD is no longer exposed to that light the shutter closes and
the light is applied on each row of the pixels in the CCD. When the last pixel is reached vertically it is
forced into the register. At that point the voltage is amplified and goes through analogue to digital
converter until the charge for the entire row is read. The computer which processes the whole thing
has two sources of information; they are the position of the pixel and the voltage in the pixel. This
whole process is repeated in the next row, and the information needed has been measured and
stored.
Definition of quantum efficiency of a pixel: “is the ratio of numbers of emitted electrons to the
number of incident photons.”
Magnification has a similar definition in Digital technology as it does in optics, it can be defined as
the ratio of the length of the image in a CCD to the length of the actual object.
Two points of an object can be resolved on a CCD if the images of the points are at least two pixels
apart.
The important thing here is that all of the things, resolution, magnification and quantum efficiency
are needed to have a good CCD. Of course the resolution will be clearer with a high pixel density. As
well as if the quantum efficiency is good then the image will require a lot less of time to from.
Bibliography:
All information and definitions taken from Physics for the IB Diploma 5th Edition by K. A. Tsokos.