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الكلية كلية التربية للعلوم الصرفة     القسم قسم الفيزياء     المرحلة 3
أستاذ المادة انتهاء عبد الله محمد       12/05/2021 07:12:45
1.1.7 Waveform Characteristics
Most waveforms encountered in digital systems are composed of a series of pulses,
sometimes called pulse trains, and can be classified:
1. A periodic pulse waveform is one that repeats itself at a fixed interval, called
a period (T). The frequency (f) is the rate at which it repeats itself and is
measured in hertz (Hz).
2. A nonperiodic pulse waveform does not repeat itself at fixed intervals.
The frequency (f) of a pulse (digital) waveform is the reciprocal of the period.
The relationship between frequency and period is expressed as follows:
f = 1/t and t = 1/f
Duty cycle is the ratio of the pulse width (tW) to the period (T). It can be
expressed as a percentage.
Duty cycle = (tW/T) 100%8
EXAMPLE: A portion of a periodic digital waveform is shown in the figure below.
The measurements are in milliseconds. Determine the following: (a) period
(b) frequency (c) duty cycle.
Sol.
a) The period (T) is measured from the edge of one pulse to the
corresponding edge of the next pulse. In this case, T is measured from
leading edge to leading edge, as indicated. T equals 10 ms.
b) f = 1/t = 1/10 ms = 100 Hz
c) Duty cycle = (tW/T) 100% = (1 ms /10 ms) 100% = 10%
1.2 The Clock and Timing Diagrams
In digital systems, all waveforms are synchronized with a basic timing waveform
called the clock. The clock is a periodic waveform in which each interval between
pulses (the period) equals the time for one bit. The figure below an example of
a clock waveform synchronized with a waveform representation of a sequence of
bits.

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