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Logic Symbology
A-62.
Switching between states takes place rapidly, and
the Schmitt trigger is therefore useful for squaring signals
that have poor rise and fall times.
It
can produce a square-
wave from a sine wave. Other uses of the Schmitt trigger are
voltage level restoration, and detection of the rise of the in-
put signal above a given level.
A-63.
ONE-SHOT MULTIVIBRATOR.
A-64.
The one-shot multivibrator (figure A-26) is a mono-
stable switching element, used to produce a pulse of pre-
determined duration. The device is triggered into its unstable
state by an external signal.
It
returns to the stable state after
a time interval determined by circuit constants.
A
IL-__
O_s_...r----
~
7900-131
Figure A-26. One-Shot Multivibrator Logic Symbol
A-65.
If
there is no inverting dot at the input, triggering
is accomplished when input A undergoes a positive-going
transition.
If
there is an inverting dot, a negative-going trans-
ition is required. The one-shot multi vibrator may have a set-
side output, a clear-side output, or both.
A-66.
The symbol for the one-shot multivibrator is al-
ways drawn with the orientation shown in figure A-26, with
the input at the left and the output or outputs at the right.
A-67.
FREE-RUNNING MULTIVIBRATOR.
A-68.
The free-running multivibrator shown in figure A-
27 can be distinguished by the letters "MV" appearing in
the symbol. This device produces trains of complementary
pulses at
Q
and
Q.
Pulse width is determined by circuit
constants.
A
1L-__
M_V_....r----
~
7900-132
Figure A-27. Free-Running Multivibrator Logic Symbol
A-8
7901A
A-69.
In some instances a control signal is applied to the
free-running multivibrator. If there is no inverting dot at the
signal input to the symbol, the multivibrator runs when the
control signal is high, and stops when the signal is low. When
it is stopped, the multivibrator is in the clear condition.
If
there is an inverting dot at the control signal input, a low in-
put is required to bring the multivibrator into operation.
This type of multivibrator is in the set condition when it is
not running.
A-70.
Figure A-28 shows typical waveforms for a con-
trolled free-running multivibrator that runs when the con-
trol signal is high. The high and low portions of the output
waveforms need not be of equal duration.
A-71.
The symbol for the free-running multivibrator is
always drawn with the orientation shown in figure A-28,
with the input (if any) at the left, and the output or outputs
at the right.
A
Q _ - - ,
7900- 133
Figure A-28. Input and Output Waveforms of Controlled
Free-Running Multivibrator
A·72.
AMPLIFIER.
A-73.
The symbol for an amplifier is shown in figure A-29.
A differential amplifier is illustrated in figure A-30. Like
gates, these symbols may be oriented in any of four positions.
INPUT
---I~>---
OUTPUT
V
7900-134
Figure A-29. Amplifier Logic Symbol
7900-135
Figure A-30. Differential Amplifier Logic Symbol
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