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of A G - G N D - D C switch.
position may be used without affecting the
result except at very low frequency (below 5
Hz).
4. Adjust the vertical gain controls for a con-
S Q U A R E W A V E
G E N E R A T O R
I N P U T
Fig. 2 8 Equipment set-up for square w a v e testing of amplifiers
Analysing the Waveforms:
The short rise time which occurs at the beginning
of the half-cycle is created by the in-phase sum of
all the medium and high frequency sine w a v e com-
ponents. T h e same holds true for the rapid drop at
the end of the half-cycle from maximum amplitude
to zero amplitude at the 1 8 0 ° or half-cycle point.
Therefore, a theoretical
alone of the high frequency components should
produce a rounding of the square corners at all four
points of one square wave cycle (see Fig. 2 9 ) .
Distortion can be classified into the following three
distinct categories:
Fig. 2 9 S q u a r e w a v e response w i t h high
frequency loss
24
However, the A C
A M P L I F I E R
C I R C U I T
B E I N G
T E S T E D
reduction
in
amplitude
venient viewing height.
5. Adjust the s w e e p time controls for one cycle of
square wave display on the screen.
6. For a close-up view of portion of the square
wave, use the X 5 magnification.
A D J U S T V E R T G A I N
C O N V E N I E N T V I E W I N G
O U T P U T
1. The first is frequency distortion and refers to
the change in the amplitude of a component of
a complex waveform. In other words, the in-
troduction in an amplifier circuit of reasonant
networks or selective filters created by com-
bination of reactive components will create
peaks or dips in an otherwise flat frequency
response curve.
2. The second is non-linear distortion and refers
to
a change
application of the waveshape to
components
tubes, an iron core transformer, and in an ex-
treme case, a deliberate non-linear circuit such
as a clipper network.
3. The third is delay or phase distortion, which is
distortion produced
between one or more components of a com-
plex waveform.
In actual practice, a reduction in amplitude of a
square wave component (sinusoidal harmonic) is
usually caused by a frequency-selective network
which includes capacity, inductance or both. The
presence of the C or L introduces a difference in
phase angle between components, creating phase
distortion or delay distortion.
wave testing of practical circuitry, w e will usually
find that the distorted square wave includes a com-
bination of amplitude and phase distortion clues.
A D J U S T S W E E P
S P E E D F O R 1
C Y C L E
D I S P L A Y
S L O P E
I N T
F O R
H E I G H T
in waveshape produced
non-linear
or elements such as vacuum
by a shift
in phase
Therefore, in square
+
by
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