Matsushita Electric Industrial Co., Ltd.

Panasonic Corporation

Hisao Kunitani

Atsuhisa Kageyama

Katsuya Ishikawa

Hidetoshi Suzuki

Satoru Tanigawa

Keiichi Ito

Hiroshi Kojima

Makoto Mizuki

Hiroshi Sonobe

Tetsuro Oomori

Yuki Kakuya

Noriko Kaku

Nobutaka Okada

Takashi Koizumi

Katsuya Isihikawa

The current drive device of the present invention includes: a current source transistor for allowing a preset drive current to flow to a drain; a cascode transistor cascode-connected to the current source transistor; a switch circuit for switching ON/OFF flow of the drive current through the drain of the cascode transistor and a circuit to be driven; and a bypass circuit for allowing the drive current to flow therethrough to bypass the switch circuit and the circuit to be driven when the switch circuit is OFF.

Current drive device

To improve accuracy of determining the average brightness level and maximum and minimum levels of the brightness signals for the entire screen. There are included a differential operation circuit that detects and differentiates rise or breaking edges in horizontal and vertical synchronous signals of an input image signal, thereby outputting horizontal and vertical differential signals synchronized with the horizontal and vertical synchronous signals, respectively; a sample window circuit that detects the beginning and ending positions of horizontal and vertical intervals to produce sample window signals established in any desired vertical and horizontal positions on the screen in accordance with the horizontal and vertical differential signals; and a brightness signal output circuit that outputs sampled brightness signals when the sample window circuit is operative.

Brightness signal processing apparatus

In a semiconductor device of the present invention, a clock is not changed instantaneously but it is changed over maximum N+1/M clocks (N: integer not less than 2) by shifting delay cells in a step by step manner to make the phase state of a previous reference signal and the phase state of a present reference signal coincide with each other, whereby the clock is synchronized with the reference signal with accuracy, and the duty of the output clock is kept constant. With this semiconductor device, it is possible to prevent the duty of the clock from being discontinuous when a signal whose reference signal does not coincide with the clock is inputted and reset is made to a rising edge of this reference signal.

Semiconductor device

An object of the present invention is to provide a signal processor which improves the offset accuracy of a video signal without increasing the number of bits of a circuit. An N-bit adder () adds a video signal (S) and an upper-N-bit signal of a brightness control signal (S) as an offset value. A 1-bit pulse generator () generates a 1-bit pulse signal (S) in which '1' and '0' have equal chances of appearing at random. A selector () selects the 1-bit pulse signal (S) when the LSB of the brightness control signal (S) is &#x201c;1&#x201d;, while selects a ground level &#x201c;0&#x201d; when the LSB is &#x201c;0&#x201d;, and supplies the selected signal to a carry input of the N-bit adder ().

Signal processor

An appropriate correction quantity is obtained for a video luminance signal on an individual video basis with a characteristic value, like the maximum or average value, of the luminance signal taken into account, thereby performing gray scale correction more effectively. A dynamic gamma correction apparatus for performing a correction on a video luminance signal includes: a correction start point control section for obtaining a correction start point, which is a lower limit of a given correction range, in accordance with a characteristic value of the luminance signal; a gamma correction quantity calculating section for obtaining a provisional correction quantity for the luminance signal to be corrected using the correction start point and the luminance signal; a gamma correction gain control section for obtaining a gain for the provisional correction quantity in accordance with the characteristic value of the luminance signal; a multiplier for obtaining a product of the provisional correction quantity and the gain as a gamma correction quantity; and an adder for obtaining a sum of the luminance signal and the gamma correction quantity and outputting the sum. The correction start point and the gain for the provisional correction quantity are controllable in accordance with the characteristic value of the luminance signal. Thus, an appropriate gamma correction quantity can be obtained as a final correction quantity.

Dynamic gamma correction apparatus

The present invention provides a color difference signal correction apparatus for correcting color difference of parts having no color, particularly white characters, which can make the correction with high accuracy also for images including lightly colored parts. The color difference signal correction apparatus of the present invention comprises a full-wave rectification circuit for full-wave rectifying an input color difference signal (R&minus;Y)a, a full-wave rectification circuit for full-wave rectifying an input color difference signal (B&minus;Y)b, an addition circuit for adding the outputs of the full-wave rectification circuit and the full-wave rectification circuit , an addition circuit for adding a white character slice level signal e and the output of the addition circuit , a luminance signal slice circuit for slicing a luminance signal g with the output of the addition circuit , and an addition circuit for adding the output of the luminance signal slice circuit and the input color difference signal (B&minus;Y)b and outputting the addition result.

Color difference signal correction apparatus

A large number of analog signals (Aa, Ba . . . Na) are time-division-multiplexed by an analog switch ( ) into a single analog signal (c). The multiplexed analog signal (c) is converted by an A/D conversion circuit ( ) into a digital signal (d). The digital signal (d) is separated by a signal separation circuit ( ) into a large number of digital signals (e) respectively corresponding to the analog signals (Aa, Ba . . . Na). Each digital signal (e) is compared by a comparison circuit (9) with a digital reference value (f) having a predetermined value. A current source control circuit ( ) generates a digital control signal (g) according to the amount of shift in the digital signal (e) with respect to the digital reference value (f), and the current source ( ) is controlled by the control signal (g). Therefore, the clamp level of an analog signal is adjusted to a predetermined level with a high precision, thereby effectively suppressing the level shift thereof.

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Kyoto, Japan

Hisao Kunitani