Portable Media Player Internal Design Trends

Tags: PMP Digital Signal Processing

Many observers and analysts agree that there will be only two hot technology topics in the field of electronic engineering and applications this year: one is wireless communication technology and the other is digital video technology.

Indeed, digital video technology has been the focus of attention in recent years, including digital video codec algorithms (such as MPEG-4, H.264, VC-1), digital video interface terminals (such as HDMI, DisplayPort), digital video broadcasting technology (such as DVB-H, Qualcomm MediaFLO), etc. Similarly, video-related application devices are also very popular. Take a look at the new generation of video game consoles (such as Nintendo Wii, Sony PS3), Apple TV released by Apple at the beginning of this year, Google's acquisition of YouTube, IPTV, HDTV, home community security, video conferencing and video calls, and you will know how popular video applications are.

Similarly, after digital portable players have replaced traditional CD (Compact Disc) players, MD (Mini Disc) players, and even digital voice recorders in large numbers, they are also actively looking for the next wave of strong growth space. The most likely development route is to add video functions, including the display of static images, the playback of dynamic images, as well as static photography and dynamic recording, which will become new directions for enhancement and improvement. In addition, the various technologies of handheld devices are also constantly improving. Therefore, this article will discuss and analyze the in-machine technology and related technologies of PMP in more detail, hoping to be helpful to industry practitioners and engineers who are planning to invest in or are currently engaged in PMP design.

Caption: Broadcom's BCM2722 mobile multimedia processor has the accelerated computing capabilities of a digital signal processor and also supports DRM (content copy protection). Apple's iPod Video uses this chip to accelerate video playback operations. The figure shows the functional block diagram of BCM2722.

Video Codec Implementation Solution

Video codec is the most critical part of PMP, but it is also the part with the most diverse and inconsistent implementation methods. According to the author's summary, there are many different implementation methods:

Application chips are designed and developed entirely for PMP needs, mostly implemented in SoC form, which can also be called ASIC or ASSP. ASIC/ASSP will use embedded processors (or controllers), even embedded digital signal processors (DSP), or hardware-line audio and video codecs.

This is achieved using a multimedia processor, such as TriMedia from Philips Semiconductor (now called NXP) or Media Processor from Sigma Designs. This type of processor usually has a VLIW architecture that can accelerate multimedia video operations.

The dual-processor (or dual-core) design uses a general 32-bit microprocessor (or microcontroller) and an additional digital signal processor. The DSP is responsible for the audio and video codec operations, while the microprocessor/microcontroller (uP/uC) is responsible for general control work and general application execution. TI's OMAP solution is a representative example. (Note 1)

It also uses a general 32-bit microprocessor or microcontroller, but the other matching chip is a codec chip that has hardware-circuited audio and video encoding and decoding operations, which is generally called a CODEC chip. If you only need the playback function, you only need a chip with hardware-circuited decoding operations, which is called a "decoder chip"; if you also want to be able to record and record in addition to playback, then you must use a "codec chip, CODEC".

Only 32-bit microprocessors and microcontroller chips are used, and all multimedia encoding and decoding operations are implemented in software. After the PMP is powered on, these calculation programs will be loaded into the PMP's system main memory, and then the processor will be responsible for executing the encoding and decoding operations of various formats.

Image caption: The Zune digital player launched by Microsoft is also equivalent to a portable media player. Microsoft Zune's market competitor is Apple iPod. The main advantage of Zune over iPod (fifth generation) is its WiFi wireless function. Zune allows users to share digital music and digital photos with friends via WiFi wirelessly, and the sharing is still managed by the DRM mechanism. (Image source: www.Microsoft.com

Comparison of the differences between various implementation methods

There is no absolute distinction between the five implementation methods mentioned above. Instead, they should be selected and used when appropriate. The advantage of choosing the first method is that it is the most cost-effective in mass production because the chip has the highest degree of functional integration and the lowest requirement for parts outside the main chip. In addition, the power efficiency is also the best. Not only is the encoding and decoding calculation part implemented in hardware, but the high degree of integration can also achieve centralized and consistent power management.

However, the disadvantage of this (first) approach is the lack of flexibility. Once there is a need to add or modify the codec algorithm, or to add other functions, or even to correct errors in the original functions, the range of adjustment is minimal. In addition, PMP is a battery-operated mobile operation, and it is not easy to use programmable logic devices such as FPGA and CPLD to increase the flexibility of hardware circuit design at this stage.

Therefore, unless the supply is of considerable volume or long-term stability, it is very rare to implement fully customized design with the least flexibility. Compared with other approaches, this approach requires more attention to debugging, verification and other procedures during chip design and development. Otherwise, if there is a need for modification in the future and other methods cannot be used to compensate, the time, effort and cost of reopening the mask and resuming production will be very high.

Next are the second, third, and fourth intermediate methods. These three methods are more flexible than the first method and are also the more common methods at present. Here is a practical example. Apple's fifth-generation iPod (also known as iPod Video) uses the third method. The microprocessor uses PortalPlayer's PP5021C-TDF Walkman main control chip (the core is 2 ARM7TDMI), and then matches it with a Broadcom BCM2722 chip. Although the BCM2722 chip is called a mobile multimedia processor, it is actually a digital signal processor. (Note 2)

Caption: The backlight of a digital player can be driven by a simple series or parallel design, but PMPs use more white LEDs and require uniform light, so they usually require a dedicated white LED driver chip. The picture shows MAXIM's white LED driver chip: MAX1707, which has a maximum drive current of 610mA and can drive three LED groups in parallel at the same time. (Image source: www.MAXIM-ic.com)

Let's look at another example. Microsoft's Zune uses Freescale's i.MX31L (ARM1136 core) as the main control chip. The chip also integrates a hardware MPEG-4 encoder, which is similar to the fourth approach. The only difference is that two discrete packaged chips are integrated into a single chip. However, Microsoft Zune is not entirely the fourth approach. Perhaps the hardware function of the i.MX31L chip can be directly used for MPEG-4 format encoding, but other audio and video formats except MPEG-4 can only be implemented using pure software, which is the fifth approach. [page]

As for the fifth method, it is exactly the opposite of the first method. The disadvantage of the fifth method is that it consumes the most power, and in addition to power consumption, it usually also requires a more efficient processor and a larger system main memory, and even requires increasing the battery capacity (which means the volume and weight will increase) to have the same continuous playback time as the first four methods. However, the advantage is that it has the highest flexibility. To add or modify any codec algorithm, it can be achieved by simply updating the firmware program, without any hardware-level adjustments. In addition, most hardware parts use general standard components (including processors), and the source and price of hardware supply are also more flexible.

monitor

For designers who are upgrading from digital walkmans to portable media players, the engineering technology for displays may also need to undergo a transformation. In the past, digital walkmans could use Color STN, OLED, etc. as displays, but in the PMP field, these two methods may have to be abandoned and TFT LCD must be used.

In addition, the colorful backlight technology (using 7 different colors of LED) that was previously used in digital walkmans is also not applicable in the PMP field (unless it is used to provide situational effects for electronic photo albums). The only technology that can be used is LED backlight technology, but only white light LEDs can be used, and it is very likely that due to power saving or price factors, it will be necessary to reconsider and evaluate the use of EL, CCFL and other backlight technologies. As a result, the power supply design for the backlight driver is also more complicated than that of LED.

Even if white light LEDs are used, the display area will be much larger than previous portable players, so a light guide plate component (3.5 inches by 7 inches) will be needed, and more design effort will be put into light uniformity.

Caption: Since PMP and other handheld devices are very particular about power saving, most of the audio power amplification methods that can be used are Class D amplification. In addition to high power efficiency, Class D amplification is also more compact than other amplification methods. The picture shows the internal functional block diagram of the 20W mono Class D amplifier: TPA3001D1 from Texas Instruments (TI). (Image source: www.TI.com)

It is worth noting that the backlight, processor, micro hard drive, etc. are the main power-consuming components in the PMP device, so special attention should be paid to power-saving design. In the automatic power-saving mechanism, the backlight should be turned off when there is no operation and no content is played (or the screen content is changed) for a certain number of minutes (preset, or allowed by the user to set), so as to save electricity.

Storage Media

In the past, the storage media of PMP was micro drives, which refer to hard drives with a disk diameter of 1.8 inches or less. The main manufacturers in this field are Toshiba, Hitachi (more accurately, HGST), Seagate, Cornice, and Magicstor. In addition to 1.8 inches, there are also 1-inch and 0.85-inch specifications.

The main consideration for PMP to use micro hard disk is the price-capacity ratio. If a VCD movie takes up 1.3GB (two 650MB discs) and a DVD movie takes up 4.7GB, and assuming that a reasonable number of portable movies is around 610 (Note 3), then at least 7.8GB47GB of capacity is required. If all of this capacity is to be achieved with flash memory, the price of a PMP will be too high for consumers to accept, so micro hard disks must be used.

Caption: Most PMP storage media are micro hard disks. Although the price of (NAND) flash memory has fallen rapidly, entry-level PMPs and entry-level to mid-level digital players have switched to flash memory, but micro hard disks still have an advantage in price-capacity ratio in the mid-to-high-level PMP and high-level digital player markets. The picture shows Hitachi's micro hard disk. (Photo source: www.hitachigst.com)

However, the situation is gradually changing. For USB flash drives, the price of a 4GB flash drive has dropped to NT$800 or NT$900. In addition, the speed at which new video compression algorithms such as MPEG-4 and H.264 are becoming more and more popular can be described as "crazy". As a result, a 60-minute video can be stored in a space of about 300MB and the picture quality can still be maintained at a certain level (Footnote 4).

Due to the interaction of the two effects, the minimum reasonable usage capacity acceptable to PMP can be revised downward, and the reasonable and practical minimum acceptable capacity and price have been adjusted. PMP equipped with 8GB12GB (NAND) flash memory can enter the market as an "entry-level model", instead of having to rely on micro hard drives like in the past.

Conclusion: Finally, other PMP-related technologies are also gradually evolving, such as faster charging efficiency (more energy can be charged in a shorter time), more extended applications (document reading, web browsing), more accurate remaining power display (from ADC measurement to coulomb power counting method), and more connection methods (USB synchronization, USB to street, wireless). These developments must also be paid attention to.

Caption: From a certain perspective, Mylo (short for My Life Online) from Sony of Japan is a PMP with a sliding cover design that combines more applications and communication functions. However, Mylo only has a built-in 1GB flash memory, which is not enough for video playback applications. However, Mylo still provides a memory card slot to expand storage capacity.