CS302 - Digital Logic & Design
© Copyright Virtual University of Pakistan
Lesson No. 01
AN OVERVIEW & NUMBER SYSTEMS
Analogue versus Digital
Most of the quantities in nature that can be measured are continuous. Examples include
Intensity of light during the day: The intensity of light gradually increases as the sun
rises in the morning; it remains constant throughout the day and then gradually decreases
as the sun sets until it becomes completely dark. The change in the light throughout the
day is gradual and continuous. Even with a sudden change in weather when the sun is
obscured by a cloud the fall in the light intensity although very sharp however is still
continuous and is not abrupt.
• Rise and fall in temperature during a 24-hour period: The temperature also rises and
falls with the passage of time during the day and in the night. The change in temperature is
never abrupt but gradual and continuous.
• Velocity of a car travelling from A to B: The velocity of a car travelling from one city to
another varies in a continuous manner. Even if it abruptly accelerates or stops suddenly,
the change in velocity seemingly very sudden and abrupt is never abrupt in reality. This
can be confirmed by measuring the velocity in short time intervals of few milliseconds.
The measurable values generally change over a continuous range having a minimum and
maximum value. The temperature values in a summer month change between 23 0C to 45 0C.
A car can travel at any velocity between 0 to 120 mph.
Digital representing of quantities
Digital quantities unlike Analogue quantities are not continuous but represent quantities
measured at discrete intervals. Consider the continuous signal as shown in the figure 1.1.
To represent this signal digitally the signal is sampled at fixed and equal intervals. The
continuous signal is sampled at 15 fixed and equal intervals. Figure 1.2. The set of values (1,
2, 4, 7, 18, 34, 25, 23, 35, 37, 29, 42, 41, 25 and 22) measured at the sampling poin