Tear Down: HD DVD player pushes the performance envelopeBecause the HD DVD standard is relatively new, there were few shortcuts to be taken by the system's designers.
This was the most complex Tear Down I've done. Most of the projects I tackle are based on a single function, and in most cases, there's an ASIC or high-end CPU that handles most of the processing functionality. In this case, there was a processor for each subsystem and lots of glue logic to tie it all together.
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First, while standard-definition DVD players have been around for along time, the HD version is relatively new. Second, the technology is far from simple. The number of bits that must be processed for both the audio and video is tremendously high. And third, because the technology is so new and evolving rapidly, the move to ASICs has not occurred yet. As you can see from the photo of the board, processors abound.
For example, to handle the audio processor, Toshiba chose an Analog Devices Sharc DSP, the 21262. The process of integrating those DSPs took roughly six months. The first interaction between the two companies occurred in early 2005. The 21262 offers 32-bit floating-point performance, which is needed for the high-quality audio processing. This includes efficiently handling 24-bit converter inputs without having an overflow and loss of bits.
The pair of Sharcs on this board are running at 200 MHz, while the family goes up to 400 MHz. ADI claims that they've also found a home in Denon, Sony, and Bose systems. The 21262 contains 2 Mbits of RAM and the 266 add 4 Mbits of ROM. That ROM space holds the audio algorithms, which include Dolby digital decoding, DTS decoding, and Dolby Pro Logic II post processing.
"That's one of the reasons our customers like these parts, because of the completeness of algorithms," says Colin Duggan, a product line director at Analog Devices. "When we go to customers, we provide the silicon, the development tools, the C compilers, assemblers, and so on, because they want to add their special algorithms that make them unique."
A powerful DSP was needed to fulfill the audio requirements of the HD DVD standard (as well as the competitive BluRay standard). Hence, the need for four Sharc processors. For example, the system requires both primary and secondary audio decode channels, effects processing, mixing, sample-rate conversion, transcoding back to the DTS Dolby digital standards in S/PDIF, and other mixing and post-processing. The final code that's running on the DSPs came from a collaboration between ADI and Toshiba.
When Toshiba set out to develop a second generation of the HD-1A, it was with the intention of reducing cost of the system, not change the features. That design contains just one 21262 DSP. They reduced the parts count by integrating a lot of the audio processing into an SoC.
"We continue to work with Toshiba on future generations of their system, and there's another Sharc in the works that they'll employ," says Duggan. It'll let them integrate more audio algorithms into one chip. For example, if they want to add more audio post processing, this new part will have the headroom to do that."
As you might expect, the DSP group within ADI works hard to collaborate with other divisions within the company, trying to help each other out when it makes sense. By putting in the hooks to make various parts operate better together, they can often offer a cost reduction for the end customer. In the case of HA-1A, both the analog and DSP divisions already had a relationship with Toshiba.
The parts delivered by the "other side of the house" include the ADV7312 video encoder and the DA4861 video filter, which essentially acts as a reconstruction filter. The ADV7312 takes the digital baseband video data from the MPEG decoder chip set, a Broadcom BCM7411. The ADV7312 contains six high-speed 11-bit DACs. There's also 16X over-sampling for standard definition signals.
"We call these devices video encoders, but some people think of them as DACs," says Peter Hall, a product marketing manager for video converters at Analog Devices. "A video encoder has a DAC inside it, but it also has some circuitry in there to encode the video signal before it's fed through the DAC. For standard-definition composite signals, you need to re-modulate the color information onto the composite video signal."
In other words, you're over-sampling the input signal to achieve a better signal-to-noise ratio (SNR) and better noise performance, which results in a higher quality picture with less noise. By over-sampling at 216 MHz, 16 times more information is added to the video signal. As a result, for every 2X increase in the over-sampling level, the SNR improves by 3 dB. In comparison, standard video DACs typically operate at 54 MHz, providing 4X over-sampling.
Hall claims that a key benefit of using a discrete video encoder like this one is that it's difficult to achieve this level of resolution and over-sampling performance with an integrated solution.
The DA4861 high-speed op amp has a bandwidth that's wide enough to cope with high-density analog video signals with good performance over the entire video signal range. Two key specs with respect to the video signals are the differential gain and phase, which specify how the signal changes when it passes through one of these components and how it effects the color and brightness information in the signal. These are areas where the ADI parts shine.
The Broadcom BCM7411 is an advanced audio and video decoder that supports MPEG-2 high-definition H.264 high-profile (4.1) and the advanced profile for VCI. These are the codecs required for HD DVD. The part also supports a number of audio codecs, although that function is handled by the Sharcs in this design.
The BCM7411 was originally designed for set-top boxes, which usually employ standard stereo audio. The HD DVD formats require multi-channel audio decoding, which requires various system-level functionalities, like mixing and speaker and phase management.
According to Doug Grearson, a senior marketing manager for Broadcom's consumer electronics group, "One of the most difficult aspects of this system has to do with the system software. If you look at these players, the standards allow for multiple video streams, multiple graphics planes, and multiple audio programs all running at the same time, and they need to be synchronized. There's a lot of stuff going on in one of these boxes and managing it all is an interesting trick."
In addition to all the horsepower previously mentioned, the board also contains an Intel Pentium 4 processor. This processor is augmented by the use of Intel Northbridge and Southbridge parts, as well as an Intel Ethernet controller.
Xilinx also claims a measure of responsibility for this design, as you can see both CoolRunner II CPLDs and Spartan III FPGAs on the board (For a related white paper on the Spartan III, click here). The CoolRunner II designed into the HD-1A does some configuration control, replaces some discrete logic, and does voltage-level shifting. These are all typical CPLD functions. The board contains four rails, giving it the ability to operate from 1.2 to 3.3 V, with stops at 1.8 and 2.5 V.
"This level shifting could be handled with discrete parts, but remember that such parts only do one function, whereas CPLDs do multiple functions," offers Kevin Kitagawa, the outbound product manager for CPLDs at Xilinx. "The CPLD can also handle configuration control, which needs the CPLDs' non-volatility. Then, the designer figures out that he has even more capability available in his CPLD. So he takes advantage of that functionality and replaces other parts on the board."
There's actually a pair of Spartan III devices on the board, the 3S1000 and the 3S1500, that are used for peripheral control. For example, the parts interface with the various peripheral buses, bringing together all the signals from those buses. The FPGAs consolidate the signals into something that can be handled by the main processor bus. Some of the more basic functions performed by the FPGAs include memory control and data multiplexing.
The bottom line with the design of the HD-1A is that it's a very complex design, but one that will be reshaped over time to be cost-reduced and performance-enhanced. This will be particularly true as the HD standard becomes more prevalent and consumers start to gobble up these boxes in high volumes.
Richard Nass is editor in chief of Embedded Systems Design magazine. He can be reached at firstname.lastname@example.org.