Nec Corporation

Kunihiko Azuma

Kenji Mori

In a color signal processing circuit capable of processing a PAL/NTSC color television signal, in order to prevent an image deterioration caused by chromatization when a signal is received in an NTSC signal receiving mode, there is provided a gate control signal generating circuit for alternately generating gate control signals 'GA' and 'GK', one for one horizontal period and the other for a next one horizontal period, in response to application of a phase inverting pulse 'R' which inverts in polarity every one horizontal period.

Color signal processing circuit capable of processing PAL/NTSC color

A phase control circuit for operating a phase shift in accordance with a control voltage comprises four differential circuits, two of which form a multiplier circuit for providing a basic function for a phase shift operation of the phase control circuit, and the rest of which cancel variations in amplitude generated during the phase shift operation. The amplitude compensation is accomplished by a construction in which a ratio of an emitter area of a first bipolar transistor in each of the differential circuits to an emitter area of the second bipolar transistor in each of the differential circuits is set at a value between 2 and 3. Alternatively, the amplitude compensation is provided by a level shift circuit providing an offset voltage in the control voltage supplied to two of the differential circuits.

Phase control circuit having a plurality of differential circuits

An oscillator circuit including a current-controlled phase shift circuit and a feedback circuit including a quartz resonator is capable of varying the oscillation frequency in accordance with control current signals. A phase shift circuit included in the current-controlled phase shift circuit includes a first low-pass filter including a resistor and a capacitor, a first buffer amplifier, a second low-pass filter including a resistor and a capacitor, and a second buffer amplifier. The phase shift circuit has a significant gain at any frequency for oscillation. Especially an oscillation circuit implemented by an integrated circuit satisfies the suitable condition in which relative value of resistances and capacitances do not vary.

Oscillation circuit having a current-controlled phase shift circuit

An automatic gain controlling circuit is associated with magnetic heads for recording and reproducing pieces of video data information on a magnetic tape, and an in-phase current component is eliminated from a recording current flowing into one of the magnetic heads through a differential amplification between two input voltage levels produced from the recording current with the in-phase current component so that a gain control voltage signal is free from a relative accuracy between circuit components causative of the in-phase current component.

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Tokyo, Japan

Kunihiko Azuma