Testing Procedure (refer to Fig. 25):
1. Connect the output of the square wave generator to
the input of the amplifier beMng tested.
2. Connect the CH2 probe of the oscilloscope to the out-
put of the amplifier.
3. If the DC component of the amplifier output is low, set
the AC-GND-DC switch to DC position to allow both
the AC and DC components to be viewed. However,
the AC position may be used to observe the AC com-
ponent only, though this will reduce the audio frequen-
cy content of less than 5Hz.
4. Adjust the vertical gain controls for a convenient view-
ing height.
5. Adjust the sweep time controls for one cycle of square
wave display on the screen.
6. For a close-up view of a portion of the square wave,
use X5 magnification.
S Q U A R E W A V E
G E N E R A T O R
A D J U S T SWEEP
S P E E D F O R 1
C Y C L E D I S P L A Y
A D J U S T V E R T
G A I N F O R
C O N V E N I E N T
V I E W I N G
H E I G H T
I N P U T
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
O U T P U T
Fig. 25.
Equipment set-up for square wave 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 the medium and
high frequency sine wave components. The same holds true
for the drop time. The reduction in high frequency com-
ponents should produce a rounding of the square corners at
all four points of one square wave cycle (see Fig. 26).
Distortion can be classified into the following three
categories:
1 The first is frequency distortion and refers to the
change in the amplitude of a complex waveform. In
other words, the introduction in an amplifier circuit of
resonant networks or selective filters created by com-
bination of reactive components will create peaks or
dips in an otherwise flat frequency response curve.
Fig. 26.
Square wave response with high frequency
loss
22
