Transcript Chapter 1.2 - Electronic Signal & Switches

EKT 121 / 4
ELEKTRONIK DIGIT 1
CHAPTER 1.2 : Electronic Signals &
Switches
Digital Signals
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Made up of a series of 1s and 0s
Represent numbers, letters, symbols, or control
signals
Timing diagram of a digital signal.
Digital Signals
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Digital system respond to digital state (0 or 1)
and not actual voltage
In timing diagram, LSB may not always be on
the right.
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Depends on which method is used
Clock waveform timing
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Timing is very important for digital signals.
Clock & timing circuits:
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Periodic clock waveforms:
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Produce clock waveforms
Trigger digital signal at precise intervals
Voltage vs time
Waveform repetitive, at specific time interval, pulse
identical.
Frequency:
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Reciprocal of clock period (tp)
f = 1 / tp
Serial & Parallel Representation
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Serial :
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Use 1 electrical conductor for data to travel
Inexpensive but slow
Can transmit only 1 bit for each clock period
Eg: Internet, computer-to-computer communication.
Parallel:
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Use separate electrical conductor for each bit
If system uses 8-bit numbers, 8 lines are required
Expensive but fast
Eg: computer-to-printer
Exercise
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Sketch serial & parallel representations of 4-bit
number 0111.
Clock frequency 5 MHz, find time needed to
transmit using both method.
LSB is transmitted first.
Switches in Electronic Circuits
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Switching from one voltage to another (0 V to +5
V)
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Cause the transitions between 0 and 1 digital levels
Make and break a connection between 2 electrical
conductors.
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Manual switch
Diodes
Transistors
Manual Switch
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Almost ideal ON and OFF resistance
ON :
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Contacts closed
R = 0 ohms
OFF :
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Contacts opened
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R = ∞ ohms
A Diode as a Switch
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Diode : allows current to flow in one direction only
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Forward biased
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Anode voltage more +ve than cathode
Allow current flow
Reverse biased
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Anode voltage equal or more –ve than cathode
Current cannot flow
A Transistor as a Switch
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Three-terminal semiconductor components that
allows an input signal at one terminals to cause
the other 2 terminals become short or open circuit.
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Emitter, base, collector
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Input signal (1 or 0) applied to base.
A Transistor as a Switch
For NPN transistor
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Apply +ve voltage from base to emitter cause collecteremitter junction short (ON transistor)
Apply -ve voltage or 0 V from base to emitter cause
collecter-emitter junction open (OFF transistor)
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Emitter, base, collector
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Input signal (1 or 0) applied to base.
END OF
Electronic Signal & Switches