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Advanced Digital Video Encoders
CCIR-601 YCrCb to NTSC/PAL: studio quality digital video at consumer video prices
by Bill Slattery
The ADV7175/ADV7176* digital video encoders convert digital video data into standard analog baseband (NTSC/PAL) television signals. These low-cost, high-performance devices encode digital YUV (CCIR-601/656 4:2:2) and square pixel component video; and they can drive EuroSCART(RGB), S-Video (Y/C) and YUV analog video signals, as well as supporting closed-captioning and Teletext. The AD7175 also includes Macrovision® antitaping (license required from Macrovision, Inc.) The digital input section interfaces gluelessly to all standard MPEG (1 & 2) Decoders. Applications encompass TV settop boxes, VideoCD, DVD, Internet/Network Computers, Web TVs and Multimedia PC Video, as well as professional broadcast/studio video equipment. Packaging in a tiny 44-Lead PQFP. Prices (10,000) start at $7.59.
Digital video: Television signals are, in the main, transmitted in standard analog format; the signal is received over an outdoor or indoor antenna, or over a cable distribution system that may have a local analog settop box to enable pay-TV channels. This system, based on the composite analog NTSC (North America, Japan) and PAL (Europe) formats, has existed for 40 years or more and has served consumers quite well worldwide. Recently, however, television broadcasting has undergone revolutionary changes. Intent on permitting existing equipment and program material to continue in use, broadcasters have had to maintain backward compatibility of the existing format but transmit and distribute it with digital processing. Analogous to the evolution from black-and-white TV to color TV, this change will allow complete backward compatibility and transparency for both program makers and television viewers. Only the medium of delivery has changed.
This digital revolution offers a new and very significant feature to viewers. The ability to compress the digital video data means that a great many more viewing channels become available to the consumer using a standard TV set. Up to six channels can now be transmitted in the bandwidth that was previously required for just one. In addition to more channels, the signal quality available in a digital system results in vastly improved displayed pictures.
Figure 1 shows the array of reception options that the home viewer has in the digital video world, including DBS (direct-broadcast satellite), digital cable (coaxial, fiberoptic, etc.) and what is oxymoronically termed wireless cable in essence, a microwave line-of-sight distribution system, known also as MMDS (multipoint microwave distribution system). The major broadcasting networks have plans to introduce a digital version of the traditional antenna-based transmission system. Besides video broadcasts, the viewer may have local video sources, such as video CD, game console or, indeed, the emerging DVD format.
Figure 1. In home digital video architectures, the encoder is key, whatever the source.
The received digitally coded TV signal must first be converted back to the traditional NTSC or PAL signal, capable of being understood by the standard TV. The settop box, or integrated receiver decoder (IRD), which interfaces (bridges the gap) between analog and digital worlds, implements these functions:
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Receive and demodulate digital signal (QAM/QPSK receiver)
Decompress the digital data (MPEG-2 Decoder)
Convert the digital data into standard TV Signal (NTSC/PAL digital video encoder).
This last function is implemented by the ADV7175/ADV7176. In addition to performing the basic D/A conversion, the device also encodes the component YUV data into the analog composite (CVBS) or S-Video (Y/C) signals for standard analog TVs.
Multimedia PC application: The ADV7175/ADV7176 are also ideally suited for video editing on PCs. Analog Dialogue 30-2 (1996) introduced the ADV601 integrated Wavelet Video Codec; combined with the ADV7175/ADV7176 and a video decoder, it provides a complete, low-cost video-capture/editing system on a PC. Like the interface to MPEG encoders, it needs no additional glue logic.
Figure 2. Encoder provides analog output of decompressed video in PC application.
Advanced NTSC/PAL digital encoder: The ADV7175/ ADV7176 has been developed in close cooperation with digital video end customers. The resulting parts integrate all the required functionality and features, plus the optimum level of performance at the price levels demanded in the consumer electronics industry.
Beyond four 10-bit DACs, the encoder incorporates our DDS (direct digital synthesis) technology with a 32-bit-wide accumulator to accurately regenerate the color sub-carrier. An extensive input port translates the digital input samples of 4:2:2 YCrCb data into the appropriate luma (Y) and chroma (UV) video signals. A two-wire, I2C-compatible port allows all functions to be programmed.
