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 digital phase shifter is provided which uses a direct digital synthesizer. The digital phase shifter is provided with a digital phase-shifted waveform signal generator in which a plurality of digital phase-shifted waveform signals having different phase shifts are stored. The generator outputs a digital phase-shifted waveform signal corresponding to a specified phase shift from a phase shift specifying section in synchronism with an oscillation signal from a PLL circuit. The output is converted to an analog form by a D/A convertor to generate a phase-shifted waveform.

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.

Abstract: A method and apparatus of calibrating electronic scales for the horizontal axis of an oscilloscope is provided. For each of two electronic scales or cursors, output voltages of a horizontal deflection circuit are generated. A measurement is made to determine a time interval in which the voltage of a sweep waveform, generated by a sweep waveform generator and appearing at the output of the horizontal deflection circuit, passes the two output voltages. The slope of the sweep waveform generated by the sweep waveform generator is adjusted such that the time interval coincides with a target time interval.

Abstract: A variable gain amplifier is provided which includes a pair of common emitter circuits. A resistance between the collectors of a pair of transistors included within the common emitter circuits is reduced by a variable resistance used for DC level correction which is connected in parallel with a variable resistance used for gain adjustment which is connected between the collectors, thereby reducing the degree of correlation between the width of a variable range of gain and a bandwidth.