New 8VSB solutions

While a conventional LMS algorithm can cancel static ghosts, it will not handle dynamic ghosts.

One of the major issues plaguing the acceptance of digital television is its inability to cope with multipath signals, often called ghosting. In analog, ghosts have little effect on reception, if you discount the fact that they can be downright annoying. When signal conditions are poor, you can still see faint pictures with fading sound. Unlike analog, with DTV you either get full service quality pictures and sound or nothing. Demultiplexing circuitry often cannot decode the correct packets at the correct time when multipath is present.

The industry has been hard at work attempting to solve this problem, since some of the blame for less than robust sales of digital sets has been placed on poor reception traced to multipath issues. In an effort to kick-start DTV set sales, Panasonic has developed a single-chip vestigial side-band (VSB) demodulator IC for digital terrestrial broadcast receivers.

The criteria set forth in the development of this new IC was quite simple: to reduce multipath interference and enable wider and more stable indoor antenna reception using a single chip of the large scale integrated (LSI) circuit type. The Panasonic chip reduces both dynamic ghosting, caused by reflection from moving objects, and static ghosting, caused by reflection from a static object. While a conventional LMS algorithm can cancel static ghosts, it will not handle dynamic ghosts.

The Panasonic chip uses a newly developed architecture called simplified variable step LMS (SV-LMS) to reduce multipath interference. This approach passes the dynamic ghost signal through a conventional analog automatic gain control (AGC) amplifier and a response digital AGC amplifier in order to eliminate interference before decoding.

The new chip, which carries the designation MN88432, has approximately 3.2 million transistors, integrates most digital and analog front-end circuitry, and includes detection circuitry, a 10-bit A/D converter and PLL circuitry. Only the tuner is off-chip. The chip takes up just one-fourth the mounting area and can be produced for only one-third the cost of previous Panasonic LSIs. In addition, its overall package size is only one-fifth that of most conventional products.

Power-wise, the chip dissipates 0.6 watts, almost a fifth of its predecessor, due to clock control technology, the reduction of international voltage to 1.8V and the use of a four-layer 0.18-micron CMOS process. The part is housed in a 100-pin leaded chip-scale package that measures 12 mm2.

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