Programmable VSB Demodulator Chip Announced By Oren Semiconductor
Oren Semiconductor Inc. today announced the industry's first programmable VSB (Vestigial Sideband) demodulator chip. The patented device will be used in the design of broadcast digital television receivers, set-top boxes, data receivers and add-in cards. These cards will allow computers to show TV programs and receive data. The device complies with the ATSC (Advanced Television Systems Committee) Digital Television Standard. The OR51210 eliminates the need for an external microcontroller because its programmable DSP can reconfigure ""on-the-fly"" all the parameters of the built-in demodulator, matched filter, adaptive equalizer, forward error correction (FEC), numerically controlled oscillator (NCO), and phase locked loop via internal registers. This architecture allows the chip to adapt itself to achieve optimum performance. The new chip contains a proprietary adaptive equalizer that improves indoor reception. The equalizer is used to eliminate ""ghosts"" or multi-path signals that can cause severe loss of data which results in loss of picture and audio information in broadcast digital TV. The built-in DSP is completely programmed via an internal 10Kbit microcode memory that is loaded using a serial or parallel interface. The chip also includes an A/D converter, demodulator, matched filter, adaptive equalizer, FEC, NCO, phase locked loop and RAM microcode memory. According to Craig Wiley, Director of Marketing, ""Television stations in major markets are now broadcasting digital TV programming and will soon add data broadcasting to bring consumers new sources of information. The rush is on to deliver new antenna-based receivers and televisions to capture this video and data information. We are providing engineers with a leading-edge demodulation technology along with programmable flexibility that allows them to accommodate a variety of features and last-minute design changes."" Better Indoor Reception The challenge with indoor reception is the primary signal may be attenuated by a wall, furniture or person. This attenuation causes the primary and multi-path signals to have similar amplitudes which makes it difficult recover the main signal. The Oren chip solves this problem through the use of an equalizer that can be reconfigured ""on-the-fly"" to optimize the recovery of the main signal. For example, the device can reallocate equalizer filter taps for longer pre-ghost coverage. Full Equalizer The OR51210 contains a full, adaptive equalizer (not sparse tap) that has 576 taps, and typically a -4.5 to +44.6 us ghost coverage range. This range allows the chip to remove a greater number of multipath or ghost signals. The equalizer can be reprogrammed for alternate pre/post ghost coverage which is important for indoor reception. Full Programmability Most of the key functions in the OR51210 can be configured via its internal DSP. As an example, the demodulator and matched filter can be programmed to match the noise characteristics of the attached tuner, and compensate for frequency distortion. The device can be programmed to filter away the audio bands which are associated with adjacent legacy analog TV signals. The chip can be programmed for channel type detection, filter training and re-acquisition upon loss of signal. The chip can also be programmed to report FEC statistics, receiver lock status and channel parameters such as S/N, equalizer tap value, broadcast standard in use, carrier and antenna positioning information. Output Data Steam The OR51210 demodulates the signal from the radio frequency tuner in a digital Television and outputs a steady MPEG-2 transport stream of data in either parallel (8 bits at 2.69Mhz clock) or serial (21.52Mhz clock) formats. This data stream is forwarded to a demultiplexer chip that divides it into multiple data streams composed of compressed video, audio and data such as Web pages. Ghost Cancellation Technology The OR51210 contains advanced technology to automatically cancels ghost (i.e., multi-path) signals that occur when RF transmissions reflect off objects such as buildings, hills and automobiles. If not eliminated, these ghosts, which are merely a nuisance in analog TV, cause severe loss of data in digital TV transmissions. Forward Error Correction The OR51210 performs forward error correction (FEC) which is an added measure of protecting the transmitted data stream according to the ATSC format. This complex technology allows the demodulator to continue to output valid data even when the transmission connection is disrupted.