Neomagic Corporation

Cirrus Logic Inc.

Krishnan C Dharmarajan

Chester F Bassetti

Mangesh S Pimpalkhare

Suresh Agarwal

Dayakar C Reddy

Modugu V Reddy

A multimedia notebook or laptop personal computer (PC) has an enhanced audio system. An external audio controller in a docking station is connected to the laptop PC's audio system using a digital-audio link. The digital-audio link uses digital signals that have high noise immunity. The high noise immunity allows the digital-audio signals to be routed through the inexpensive docking connector, which has many other noisy, high-speed signals. Dedicated, expensive, noise-prone, and difficult-to-connect analog-audio connectors between the laptop PC and the docking station are eliminated. Analog-digital converter audio CODEC's are placed in both the docking station and in the laptop PC. A master mixer in the laptop PC mixes digital audio from the external audio controller in the docking station with digital audio from an external audio controller inside the laptop PC. The master mixer also connects to a zoom-video audio port and to an internal PCI bus for storing and retrieving audio clips. Audio from external docking-station sources and from internal sources can be freely mixed with the master mixer connected to local mixers in the audio controllers. Audio can be simultaneously played to both internal and external docking-station speakers.

Portable-PC audio system with digital-audio links to external audio in a docking station

An image displayed on a digital display such as a flat panel display is rotated while the same image is displayed on a cathode ray tube display in unrotated form. When image rotation is selected, the read address sequence into a frame buffer may be reversed and the bit read sequence may be reversed. Thus a frame of panel pixel data stored within the frame buffer of an external video memory may be scanned onto a flat panel to display a rotated image.

Image rotation for video displays

A graphics controller uses spread-spectrum techniques to modulate the pixel clock over a range of frequencies, reducing the maximum intensity of EMI emissions. When the clock input to the graphics controller is replaced with a modulated clock, the image on a CRT is distorted. Distortion is avoided by only modulating the clock to the flat-panel LCD interface. The vertical and horizontal timing signals for both the CRT and the LCD are generated from the un-modulated clock. Using the un-modulated clock for these critical timing signals ensures that each horizontal line is displayed for the same period of time. Brighter and dimmer lines are thus avoided. A second embodiment modulates the clocks to the CRT and LCD, reducing emissions for both interfaces. Even the timing signals use the modulated clock. The frequency sweep of the modulated clock is reset at the end of every horizontal line. Thus all lines are displayed for the same period, although the transfer of pixels within a line are modulated. Even though the pixel clock is modulated while pixels are written to the displays, the same sequence of modulations is repeated for each line. Thus pixels from different lines are aligned and zig-zag and wiggle distortions seen when simple asynchronous modulation is applied to all clocks is avoided.

EMI reduction for a flat-panel display controller using

Master digital mixer with digital-audio links to external audio in a

EMI reduction for a flat-panel display controller using horizontal-line

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Fremont, CA, United States of America

Krishnan C Dharmarajan