Digital Technology Topic 14

Analogue and digital signals 14.1 Analogue and digital signals

14.1.1 Analogue and digital signals An analogue signal has the same variations with time as the information itself. The values of its p.d. are continuous. A digital signal consists of high and low values of pd only with no other values of pd in between. Usually, the high values are considered to be 1s and the low values are 0s.

14.1.1 Analogue and digital signals An analogue signal has the same variations with time as the information itself. The values of its p.d. are continuous. A digital signal consists of high and low values of pd only with no other values of pd in between. Usually, the high values are considered to be 1s and the low values are 0s.

14.1.1 Analogue and digital signals A device records the analogue input and converts it to a continuously varying voltage signal which is sent to an analogue-to-digital converter (ADC). This then samples the signal at a specific rate determining the value of the voltage at those points. The device then converts that value to a digital number. which is sent to the computer processor.

14.1.1 Binary numbers Decimal Binary 1 00000 2 00001 3 00010 4 00011 5 00100 6 00101 7 00111 8 01000 9 01001 14.1.1 Binary numbers Binary system of numbers is a base-two method of counting, whereas a decimal number is a base 10 counting system. Each binary digit is called a bit. Each bit can have a value of 0 or 1, and going higher increases the number of bits by 1. The digit on the left side is called the Most Significant Bit (MSB) and is associated with the highest power of 2. The right side is the Least Significant Bit (LSB) and has the lowest effect on the number.

14.1.1 Converting binary to decimal 10101 1 x 24 0 x 23 1 x 22 0 x 21 1 x 20 16 + + 4 + + 1 21 14.1.1 Converting binary to decimal Binary system of numbers is a base-two method of counting, whereas a decimal number is a base 10 counting system. Each binary digit is called a bit. Each bit can have a value of 0 or 1, and going higher increases the number of bits by 1. The digit on the left side is called the Most Significant Bit (MSB) and is associated with the highest power of 2. The right side is the Least Significant Bit (LSB) and has the lowest effect on the number.

14.1.2 Storage of data Methods of storage has improved over time as technology and manufacturing techniques have become more refined.

14.1.2 LP The grooves in the vinyl disk cause a pin to vibrate up and down as it rides over them. The pin moves an electromagnet which converts the movement of the pin into an electrical signal which is played through a speaker.

14.1.2 Cassette Tape Tape made of magnetic materials such as Iron Oxide or Chromium Oxide. This can be magnetised by an electromagnet when the electrical signal passes through the wire. This produces an identical analogue signal in the magnetic particles in the wire. When played, the process works in reverse.

14.1.2 Floppy disks Work similarly to cassette tapes in that they consist of a tape with a magnetic material in it which can be magnetised and made to align in accordance with a digital signal rather than an analogue one. The data on the disk is given an "address" and the motor knows where to access the information.

14.1.2 Hard disks Hard disks work like a combination of floppy disks but uses material which is harder and has much more densely packed magnetic domains allowing for an increased storage capacity. Also, there are multiple "platters" of disks multiplying the storage capacity.

14.1.3 DVDs and interference CDs and DVDs work similarly to each other. They consist of a refractive material which as grooves in it. The grooves cause diffraction of the light onto it. The light reflects off the disc causing destructive interference. As the laser shines on it there are moments when the light goes into the grove and does not get reflected. The photodiode records this absence of light as a zero digitally.

Constructive Destructive Land Pit Path difference created by a pit depth of λ/4 14.1.3 DVDs and interference CDs and DVDs work similarly to each other. They consist of a refractive material which as grooves in it. The grooves cause diffraction of the light onto it. The light reflects off the disc causing destructive interference. As the laser shines on it there are moments when the light goes into the groove and does not get reflected. The photodiode records this absence of light as a zero digitally.

14.1.2 CDs and DVDs Changing the laser light to a shorter wavelength increases the resolution of diffraction that occurs. This allows for tighter tracks and smaller distances between pits. This increases the available storage space.

14.1.3 DVDs and interference An increased sample rate, obviously requires a larger amount of storage. With a DVD we are able to do this and the digitised values are a closer approximation to the original signal.

Easily manipulated, edited or processed. (digital film vs camera film) Easily compressed (reduce storage space - e.g. zip) Retrieval speed much higher. Does not affect the quality of recorded information. No degradation in data. 14.1.6 Digital advantages