When two equal voltages of equal frequency but with a phase shift (not equal to 0°C or 90°) are applied to a CRO, we obtain :

When two equal voltages of equal frequency but with a phase shift (not equal to 0°C or 90°) are applied to a CRO, we obtain an ellipse.

Key Points

•  The lissajous figure is a pattern that is displayed on the screen when sinusoidal signals are applied to both horizontal & vertical deflection plates of CRO.
• These are used to measure the frequency of the given signals and the phase difference between the signals.
• From the shape of the Lissajous pattern displayed on the CRO screen information about the relative phases of signals and the frequency ratio of signals can be determined.
• It is not used for precise measurement; it depends on the type of signal.
• If one frequency is an integral multiple (harmonic) of the other, the pattern will be steady. If not, the figure will not be stationary.

Additional Information