The ability to capture high-definition (HD) video in affordable, high-definition camcorders, digital still cameras, and personal media players has created confusion over which display interface is now the best choice. After taking advantage of significant price decreases in LCD-TVs and plasma TVs during 2006, many consumers are interested in upgrading all their video “appliances” to the HD format, so they can enjoy all of their video and images in high definition. While making this transition to high definition with new HD handheld video appliances, it only makes sense to also upgrade to a higher quality interface to connect them to their HD displays.
Several display interfaces are popular with standard definition (SD) video appliances. Commonly found on digital still cameras (DSC) and video camcorders are the analog composite (NTSC, PAL and S-Video) outputs, and sometimes the component (YPbPr) outputs that were used to connect directly to analog CRT-TV displays. IEEE-1394 and USB are digital interfaces that have become popular for connecting video portables to PCs.
Figure 1: HD camcorder block diagram
The HDMI (High-Definition Multimedia Interface), which was developed for connecting HDTVs and DVD players, is a high-bandwidth digital interface that combines audio and video over a single cable. Of all available interface choices, only HDMI offers the bandwidth necessary to support the transfer of uncompressed, pure digital HD audio/video signals between compatible devices.
Until recently, HDMI transmitters were not well suited for battery-powered handheld applications. Designed specifically to meet the requirements of DVD players/recorders, they were too power hungry and physically large for handheld applications. With battery-powered devices, every additional milliwatt is critical because the extra power consumption shortens battery life and adds to the size, weight and cost of the device. “Smaller is beautiful” is the mantra for all handheld device designers, and reducing the size and weight of individual components is an ongoing challenge.
As the availability of in-home HD displays increased, a growing need developed for connecting these good-looking displays with higher quality video and audio interfaces. Price reductions on 6M pixel and greater DSCs, new 1080i HD video camcorders, and personal media players (video iPods) have led to an increase in the number of consumers using these higher quality display sources. The existing analog (component and composite) video and digital (1394 and USB) interfaces require use of compressed digital video formats. The HDMI interface, with its broad acceptance in HDTVs, is the best choice for a higher quality, non-compressed digital interface for these new high-definition handheld devices. HDMI has become the de facto standard for the HD digital interface designed into HDTVs. DVD players/recorders, set-top boxes (STB) for cable TV, and satellite TV and A/V receivers are now available with HDMI interfaces for transferring HD audio and video information to HDTVs. All that was missing were HDMI transmitters that were designed to meet the demanding requirements of battery-powered, handheld devices.
Next: Low power HDMI transmitters
Low power HDMI transmitters
The latest generation of HDMI transmitters offers many features that are essential to designers of handheld devices. By utilizing advanced mixed-signal design techniques, active power reduction up to 50% and power-down/standby power reduction of up to 90% have been realized. New packaging options now available for HDMI transmitters offer 75% smaller footprints with no sacrifice in features or overall performance. At the same time, additional consumer requirements for supporting 5.1 surround-sound audio and extended temperature range have been added to these HDMI transmitters designed for portable applications.
The design of HDMI transmitters for low-power operation requires the use of advanced mixed-signal design techniques coupled with knowledge of the system-level application. Reducing leakage currents throughout an IC helps lower both the active power and the power-down/standby power consumption. Earlier versions of HDMI transmitters used a 1.8-V supply for the logic core and 3.3-V supply for the I/O pins.
The latest HDMI transmitters use a single 1.8-V supply, resulting in lower overall power consumption. Eliminating a supply obviates the need for a voltage regulator and several passives, saving valuable board space. Newer HDMI Tx designs also save power by incorporating 5-V tolerant pins for the HPD (Hot Plug Detect) and DDC (Display Data Channel) lines specified by the HDMI Standard. Older transmitter designs could not support 5-V input on these pins and required external voltage translators that consumed power and board space. By combining all of these improvements in HDMI transmitter design, the resulting power reductions and simplified system designs have enabled their use in battery-powered applications.
HDMI Transmitter Packages
Squeezing HDMI transmitters into smaller packages allows designers to develop ever smaller handheld devices. Early HDMI transmitter products were developed for DVD players/recorders, and the package of choice was the LQFP (leadframe quad flatpack). Using smaller LFCSP (leadframe chip scale package) and even smaller BGA (ball grid array) packages have reduced the footprint up to 75% in applications where size is critical. Integrating system functions that can reduce the number of external support components and passives also reduces the board space required for an interface. The combination of smaller packages and a higher level of integration have optimized the latest HDMI transmitters for battery-powered handheld devices.
Content protection is an optional feature in the HDMI standard that may be required in some portable applications and not in others. Cameras such as DSCs and HD video camcorders may not require content protection since the recorded images were created by the camera owner. Personal media players (PMP) with the capability to download protected content (purchased legally from websites such as iTunes, Unbox, Vongo and others) will require support for content protection. In order to display protected content on an HDTV, the HDMI transmitter must support HDCP (High definition Digital Content Protection). HDMI transmitters such as Analog Devices' AD9387 (internal HDCP key storage) and AD9387NK (external or no HDCP key storage) offer designers the flexibility to support content protection in the same board footprint with internal or external key storage, or no key storage, saving cost when content protection is not required.
Figure 2: HDMI transmitter block diagram
Audio-support in battery-powered handheld devices continues to expand, producing a more realistic entertainment experience. Initially DSCs and video camcorders had support for stereo (2 channels) audio. Recent advancements in microphone technology now enable multi-channel surround sound (5.1 audio) in the latest HD camcorders. The new HD PMPs are designed to download and playback HD video content, so they need to support 5.1 audio output. It is important that the HDMI transmitters used in these portable applications are capable of supporting 5.1 audio for high-quality audio reproduction, yet still meet the needs for cost-sensitive applications where stereo audio is specified.
Next: Environmental requirements for HDMI transmitters
The environment in which battery-powered handheld devices are used by consumers frequently extends well beyond the commercial temperature range (0 deg. C to 70 deg. C) specified for most consumer-electronics equipment. These portable devices may spend hours in a car trunk at extreme summer or winter temperatures; yet consumers expect them to operate properly immediately after being connected to a HDTV. This is why ICs used in these applications are now being specified for the industrial (-25 deg. C to 85 deg. C) temperature range. HDMI transmitters used in these demanding portable applications now provide full-rated performance over these extended temperatures.
Recent developments in HDMI transmitters are now enabling HD performance in battery-powered handheld devices. While the first “wave” of HDMI transmitters was developed specifically for DVD player/recorders, power consumption and package sizes were too large for these demanding portable applications. IC designers have recently achieved significant power and package size reductions, added support for content protection and 5.1 audio, and extended the operating temperature range of the latest HDMI transmitters. The proven HDMI interface is now capable of providing consumers with a high-quality, non-compressed HD digital interface for audio/video from their battery-powered handheld devices.
Figure 3: AD9387 block diagram
About the author
Doug Bartow has been responsible for defining display interface products at Analog Devices over the last ten years for LCD monitors, projectors, plasma displays and HDTVs. Prior to ADI, he worked in product marketing and product development at Harris Semiconductor (now Intersil) and at Motorola. He can be reached at .