Abstract: A signal processing circuit for a vector scope adapted to display and measure characteristics of a color video signal on a screen which comprises a variable gain circuit 3, a demodulation circuit 6, timing signal generator 7, amplitude detection circuits 8,9, memory 12 storing a reference amplitude and CPU11. An input signal V.sub.in through the variable gain circuit is supplied to demodulation circuiting from where chrominance components R-Y, B-Y are provided to the amplitude detection circuits. When the timing signal is provided to the amplitude detection circuits, the circuits detect their amplitudes. The CPU computes an amplitude of a burst signal in accordance with the detected amplitudes and the difference between the computed amplitude and the reference amplitude stored in the memory. If the difference is not zero, the CPU controls the variable gain circuit so that it become zero.

Abstract: A phase shifting device for a vectorscope is provided which enables a vector-displayed waveform to be instantaneously and accurately rotated to an arbitrary or variable predetermined target phase position, with an arbitrary or variable predetermined portion of the vector-displayed waveform being selected as a reference for phase shifting. The phase shifting device includes first and second phase shift input generators. The first generator produces a first phase shift input signal representative of an arbitrary amount of phase shifting. The second generator produces a second phase shift input signal representative of a predetermined amount of phase shifting for the instantaneous and accurate rotation of the vector-displayed waveform.