[Product Innovation]
Controller IC Is Gateway To Multiple, Secure A/V Sources
Multiple transport ports, plus a variety of demultiplexing and descrambling algorithms in a single IC, fulfill the requirements of personal video recorders and set-top boxes.
A Look At The Arriving Stream The local bus controller is an 8- or 16-bit bus (selectable) that can be used for connecting peripherals of varying types—like Flash, EPROM, and other I/Os as required. So if there are miscellaneous I/Os that need to be controlled externally, the local bus is a good way to do it. For instance, ISAs and 68k-style peripherals can be connected and the STB/PVR controller IC local bus controller can be employed to access and control them. The local bus acts as a Flash bus, as well. This enables booting up the entire set-top box from one set of Flash connected to the local bus.
The ICAM Block is a dedicated descrambler for decoding systems that are enabled by New Data Services (NDS). It's their conditional access mechanism. In combination with a SmartCard, the ICAM block can be activated to descramble arriving NDS protected data streams. This is popular in Europe.
The signal arriving at a DTV tuner or set-top box is rf. The arriving rf signal from either a terrestrial, satellite, or cable source passes though a DTV tuner to a demodulator. As it passes through the front-end device, it's digitized and applied to one of the transport inputs of the STB/PVR controller IC. What arrives at the STB/PVR controller IC is a data stream chopped up into 188- or 130-byte packets. This complies with the ATSC standard for high-definition TV digital transmission, which defines this 188-byte packet. (This is the MPEG-2 transmission format, as well.) There also are proprietary standards, such as DirecTV, that employ 130-byte packets. In some cases, the format, as well as the length, varies. The algorithms stored in the STB/PVR controller IC are designed to comply with these various standards.
Pause-And-Play TV Because the STB/PVR controller IC has enough ports and processing capability to receive multiple transport streams, it can readily handle PIP. For example, two tuners may be connected to the STB/PVR controller IC via the transport input ports (Fig. 2). The IC will process both streams simultaneously, decrypting one or both, as necessary. It can do this because it has two identical descrambler blocks. The composite PIP can then be forwarded to the demux and next fed to a DTV decoder for separating out the video, audio, and data.
Although PIP is relatively simple, there might be cases in a PVR system when the viewer wishes to use the third transport stream. For instance, in addition to having PIP active, there could be a requirement to simultaneously record data arriving at the third transport port for subscription/nonsubscription data devices.
A lot of the TV and set-top box companies have been quite surprised by the success of PVR manufacturers. They're eager to take advantage of the opportunities arising as PVR is catching on.
What is really novel about PVR is that it enables viewers to pause live TV. The arriving stream is decrypted, if necessary, and loaded directly onto a hard disk at the same time it's being read, fed through the demultiplexer, decoded, and forwarded on to the viewing screen (Fig. 3). There's only a fraction of a second delay between the content loading on the disk drive and the content being viewed on the screen.
The trick is to do it in real time—to write to the disk at the same time that it's being read. Once the viewer presses the pause control, the disk must continue recording the arriving transport flow in anticipation that the viewer will want to resume viewing shortly.
One might ask if the transport stream is always descrambled before it's demuxed. The designer has to decide whether to descramble the transport stream before or after it's demuxed. Descrambling a stream before it's fed to the hard drive is technically simpler. The content industry, however, prefers the descrambling to be delayed until after the streams are read from the disk. That's because, in theory, the disk drive is removable (Fig. 4). Therefore, it might be possible to connect it to a PC to permit unauthorized, decrypted content to be fed to an unauthorized screen.
Normally, the descrambler requires that a valid SmartCard be connected. The SmartCard, in effect, gives the descrambler a key that enables a particular algorithm. The algorithm uses this key as part of the descrambling mechanism. With the wrong key, of course, the viewer receives an unintelligible transport stream. These keys are automatically changed every so often.
Another technique for protecting the content involves stripping out the time stamp associated with the incoming data and manipulating the signals during demultiplexing. The PVR/STB controller can do this.
As video gobbles much disk space, the STB/PVR controller IC can manage arriving data to conserve the space. Say a particular disk drive can store 10 hours of video, but not all of the information arriving on any transport stream is of interest to the viewer. A 6-MHz TV channel may contain four or five standard-definition channels for instance. Instead, the 6-MHz band might carry a few standard-definition channels plus a data channel. Most likely, a viewer would wish to record only one of these channels. The arriving data stream can first be descrambled, if necessary, and then fed to the demux. There, the unwanted channels can be discarded so only the desired information is forwarded to the hard drive for storage (Fig. 5).
Price & Availability There are three versions of the STB/PVR controller IC. Each comes in a 324-pin BGA package. The TL810 is designed for worldwide satellite applications—including DirecTV (USA), ARIB (Japan), and DVB (Europe). The TL811 also is suitable for worldwide satellite applications, but it will handle cable and terrestrial systems as well. This includes capabilities for ATSC, which is the U.S. standard for terrestrial digital transmission, and OpenCable for U.S. cable applications. The TL821 provides all of the capabilities of the TL811, plus a second demux, enabling simultaneous decryption from two transport streams. Prices range from $15 to $20 in high volume. The devices are available now.
TeraLogic Inc., 1240 Villa St., Mountain View, CA 94041; (650) 526-2000; fax (650) 526-2006; www.teralogic-inc.com.
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