They illustrate one of the earliest uses to which the CRO was put. Lissajous patterns are formed when two sine waves are applied simultaneously to the vertical and horizontal deflecting plates of a CRO. The two sine waves may be obtained from two audio oscillators as shown in Figure. Obviously, in this case, a sine wave sweeps a sine-wave input signal. The shape of the Lissajous pattern depends on the frequency and phase relationship of the two sine waves.
produce a straight line, an ellipse or a circle depending on their phase difference
(below figure).
In general, the shape of Lissajous figures depends on
(i) Amplitude,
(ii) Phase difference and
(iii) Ratio of frequency of the two waves.
Lissajous figures are used for
(i) Determining an unknown frequency by comparing it with a known frequency
(ii) Checking audio oscillator with a known-frequency signal and
(iii) checking audio amplifiers and feedback networks for phase shift.
