A video signal synthesizer for producing a picture-in-picture effect on a display device utilizes a phase locked loop circuit to generate a carrier wave synchronized with a color burst signal of a composite video signal representing a main picture to be reproduced, which carrier wave is used to modulate a time compressed second composite signal which represents a sub-picture to be superimposed on the main picture. A time division multiplexer is used to multiplex the first and time compressed second video signals to produce a picture-within-a-picture video signal for application to the receiver of a display device. By using a carrier wave generated from a phase locked loop circuit, the color subcarrier signals of both the main and sub-picture signals have the identical frequency.
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