Hitachi, Ltd.

Yukinari Ueki

Tomomitsu Kuroyanagi

Shuzo Matsumoto

Masanori Kamiya

Satoshi Takahashi

Hideaki Ohki

Eiji Takagi

Koji Kamogawa

The aperture correction circuit of the present invention comprises a preshoot signal generator which generates the preshoot signal of the edge part of a video signal, an overshoot signal generator which generates the overshoot signal of the edge part of the video signal, a shoot signal composition circuit which adds the preshoot signal and the overshoot signal at an addition ratio corresponding to a control signal, thereby to deliver the resulting signal as a correcting shoot signal, and an adder which adds the video signal and the correcting shoot signal, thereby to deliver the resulting signal as an output, wherein the shoot signal composition circuit is supplied as the control signal with a signal which changes according to the input video signal, such as the differentiated signal of the input video signal. Thus, the ratio between the preshoot signal and the overshoot signal is dynamically changed according to the input signal, so that an image quality can be adjusted according to the input video signal.

Aperture correction circuit

A phase shift circuit comprises a variable phase shifter responsive to an externally supplied voltage to change the amount of phase shift, and a phase detector operative to detect a phase difference between input and output signals of the variable phase shifter and supply a voltage complying with the phase difference to the variable phase shifter. When the center frequency of the variable phase shifter is changed by reason of production errors and temperature variations to deviate the phase shift amount from a desired value, the phase detector controls the center frequency such that the phase shift amount can be fixed to the desirably predetermined value.

Phase shift circuit for electrical signal

An amplifier suitable for use as an active filter such as a low-pass filter, a high-pass filter or a phase shifter, which can be easily formed as part of an integrated circuit. The amplifier includes first and second transistors, which together form a first differential amplifier for converting the voltage of the input signal thereto to a signal current. It also includes third and fourth transistors, which together form a second differential amplifier for dividing the signal current from the second transistor in a given ratio. A capacitor is connected to the collector of the fourth transistor, and first and second resistors are connected, respectively, to emitters of the first and second transistors. The current division ratio of the current flowing through the third and fourth transistors is controlled by a control voltage DC supplied to the base of the third transistor and the base of the fourth transistor. In the amplifier, the signal current shunted in the current division ratio K between the third and fourth transistors flow through the load capacitor so that the time constant of the active filter is controlled, the ratio K being controlled by the control voltage V.sub.c. The control voltage V.sub.c also compensates for the inaccuracy of the values of the resistors and capacitors.

Amplifier circuit suitable for use as an active filter circuit

Growing community of inventors

Yokohama, Japan

Yukinari Ueki