Types of Conversions Cont

Conversion Digital to Analog Conversation o    Process of changing one of the characteristics of an analog signal based on the info in a digital signal o    When you Tx data from one computer to the other using a public telephone line o    Original data is digital but because telephone wires carry analog signal, original data must be converted o    Digital data must be modulated on an analog signal that has been manipulated to look like two distinct values corresponding to binary 1 to binary 0 o    Figure  shows  the  relationship  b/w  digital  info  the  digital  to  analog  conversion hardware & resultant analog signal ™   Variation in Characteristics of Sine Wave o    A sine wave is defined by 3 characteristics:    Amplitude    Frequency    Phase o    By  changing  one  aspect  of  a  simple  electrical  signal  back  & forth,we can use it to represent digital data o    When we vary any one of these characteristics ,we create a second version of that wave o    If  we  than  say  that  the  original  wave  represents  binary  1,the  variation  can represent binary 0 or vice versa o    So  by  changing  one  aspect  of  a  simple  electrical  signal  back  &  forth,we  can use it to represent digital data ™   Mechanisms for Modulating Digital Data to Analog Signals o    Any of the three characteristics listed above can be altered in this way, giving us at least 3 mechanisms for modulating digital data into analog signals    Amplitude shift keying(ASK)    Frequency shift keying(FSK)    Phase shift keying (PSK) •     Fourth Mechanism o    In  addition,  there  is  a  fourth  and  better  mechanism  that  combines changes  in  both  amplitude  and  phase  called  Quadratue  Amplitude Modulation(QAM) o    QAM is the most efficient of these options and is the mechanism used in all modern modems