X-Y O P E R A T I O N A P P L I C A T I O N S
Phase Measurement:
Phase measurements may be made with an os-
cilloscope. Typical applications are in circuits designed to
produce a specific phase shift, and measurement of phase
shift distortion in audio amplifiers or other audio networks.
Distortion due to non-linear amplification is also displayed
in the oscilloscope waveform.
A sine wave input is applied to the audio circuit being
tested. The same sine wave input is applied to the vertical
input of the oscilloscope, and the output of the tested circuit
is applied to the horizontal input of the oscilloscope. The
amount of phase difference between the two signals can be
calculated from the resulting Lissajous' waveform.
To make phase measurements, use the following
procedures (refer to Fig. 21).
A U D I O
S I G N A L
G E N E R A T O R
A U D I O
N E T W O R K
B E I N G T E S T E D
Fig. 2 1 .
Typical phase measurement alignment set-up
1. Using an audio signal generator with a pure sinusoidal
signal, apply a sine wave test signal to the audio
network being tested.
2. Set the signal generator output for the normal
operating level of the circuit being tested. Observe the
circuit's output on the oscilloscope and if the test cir-
cuit is overdriven, the sine wave display is clipped and
the signal level must be reduced.
3. Connect the CH1 probe to the output of the test cir-
cuit.
4. Set the S W E E P TIME/DIV to X-Y.
5. Connect the CH2 probe to the input of the test circuit.
6. Adjust the CH1 and CH2 gain controls for a suitable
viewing size.
7. Some typical results are shown in Fig. 22. If the two
signals are in phase, the oscilloscope trace is a straight
line. If the vertical and horizontal gain are properly
adjusted, this line is at 4 5 ° . A 90° phase shift
produces a circular oscilloscope pattern. Phase shift
of less (or more) than 90° produces an elliptical
Lissajous' pattern. The amount of phase shift can be
calculated by the method shown in Fig. 23.
Fig.
22. Typical phase measurement oscilloscope
displays
20
L O A D
NO A M P L I T U D E . D I S T O R T I O N
N O P H A S E S H I F T
A M P L I T U D E D I S T O R T I O N
NO P H A S E S H I F T
1 8 0 ° O U T O F P H A S E
N O A M P L I T U D E D I S T O R T I O N
P H A S E S H I F T
A M P L I T U D E D I S T O R T I O N
P H A S E S H I F T
9 0 ° O U T O F P H A S E
