Mobile High-Definition Link
(MHL™)
What is MHL?
MHL technology is an audio/video interface that connects portable consumer
electronics devices, such as mobile phones, digital cameras, camcorders and
portable media players, to HDTVs using a single cable via the television’s
standard HDMI® input port. MHL technology was developed by Silicon Image, Inc., a
founding member of the HDMI standards body and a leading manufacturer of HDMI
semiconductors and intellectual property.
How will consumers benefit from MHL technology?
A tremendous amount of multimedia content, from high-resolution images and short
videos to feature-length Hollywood films, is downloaded, captured and/or stored
on portable personal entertainment devices. Unfortunately, when consumers
connect these portable devices to an HDTV via standard analog connections, the
picture is often displayed with image quality below standard definition.
MHL-technology enabled devices, however, can connect to HDTVs via a standard
HDMI port found on most televisions sold today, allowing users to watch and
listen to multimedia content on a large screen in high definition.
How is MHL technology implemented in mobile CE devices?
To equip a mobile device with MHL technology, the manufacturer would add an MHL
transmitter IC to the mobile device. Four pins on the device’s connector need to
be reserved for audio/visual Transition Minimized Differential Signaling (TMDS)
packets and a single pin is reserved for a control bus, which supports
authentication, A/V format discovery, and various control functions.
Initially,MHL technology enabled mobile devices will connect to the DTV via a
docking station or dongle, which includes an HDMI-to-MHL bridge IC that performs
the conversion from the lossless MHL media format into a standard HDMI
compatible signal. The docking station is equipped with a standard HDMI output
connector, allowing the docking station to be plugged directly into HDTVs. The
docking station can also pass AC power through to the mobile device to charge
the battery when the device is in the dock and an optional USB connector will
allow the device to exchange data with a PC. DTV manufacturers may integrate MHL
technology compatible HDMI receivers and input processors into their DTV
platforms. These DTVs will be capable of accepting MHL input directly from the
mobile device without needing a docking station bridge.
Why not just equip the mobile device with HDMI output?
Physical space for connectors on portable mobile devices such as digital
cameras, portable media players and mobile phones is often extremely limited due
to the small form factors of these devices. Mobile device manufacturers
generally prefer to have a single proprietary connector that accommodates AC
power, USB and audio/video transfer. The standard HDMI interface would require
19 pins on this connector, which can make the standard HDMI interface difficult
to implement on small devices. MHL technology reduces this pin-count requirement
from 19 to five, without compromising audio/video quality or HDMI compatibility,
to allow for a smaller, multi-functional connector.
In addition to connector size limitations, an IC’s power requirement is another
important consideration for mobile device manufacturers because this affects
battery life, a feature that significantly influences many consumers’ purchase
decisions. The low active and standby power consumption of MHL transmitters
dramatically extend battery life in mobile devices. In the active setting at
720p and 1080i, typical MHL transmitters consume no more than 40 milliwatts
(mW). On standby mode, the transmitters consume just 30 microamps (µA). These
MHL transmitter power draw specifications can be up to 10 times lower than
typical HDMI transmitters.
Why not just use an analog connection between the dongle and the HDTV?
Component video requires three video connectors plus stereo audio connectors or
a multi-channel audio optical connector, for a total of five to six connectors.
This puts a burden on the manufacturer to integrate a larger dock connector. In
some cases, manufacturers have implemented a serial dock interface for the
compressed media and then decode the media using a digital signal processor in
the dock, an expensive solution duplicating the functions in the mobile device.
MHL technology solves this problem with a low-cost, low-pin count interface.
Does MHL technology support CEC?
The Consumer Electronics Control (CEC) interface block provides CEC compliant
signals between CEC devices and a CEC master. A CEC controller using the Silicon
Image CEC Programming Interface (CPI) is included on-chip. This CEC controller
has a high-level register interface, accessible through the I2C interface, which
is used to send and receive CEC commands. This controller makes CEC
implementation very straight forward, removing the burden from the host CPU to
manage bit transitions on the CEC bus. In the MHL application, the CEC/CPI logic
is implemented as a distributed solution. The CPI registers are accessed by the
host through the MHL transmitter I2C registers, but the actual CEC operation
occurs in the MHL receiver.
In Summary, what are the key features of MHL technology?
- MHL technology provides HD audio/video with only five pins, allowing a tiny
connector suitable for mobile devices;
- MHL technology conserves battery life with ultra-low active and standby power
draw;
- MHL technology supports high-quality digital HD video over a single cable with
resolutions up to 1080p;
- MHL technology is compatible with the HDMI input ports found on most DTVs today;
- MHL technology includes integrated CEC functions and arbitration logic.
What products that support MHL Technology are available?
MHL Transmitters are low pin-count digital media transmitters featuring a single
data lane Transition Minimized Differential Signaling (TMDS) solution, which
reduces pin count for small devices. These transmitters can deliver full
high-definition (HD) video and digital audio through five pins on miniature
connectors. When combined with an MHL bridge, MHL transmitters form an
HDMI-enabled source device fully compliant to HDMI compliance test
specifications. MHL Transmitters are available with support for Mobile Industry
Processor Interface (MIPI) input or parallel RGB digital video input. The low
active and standby power consumption of MHL transmitters extend battery life in
mobile devices.
VastLane SiI9226 MHL Transmitter with Parallel RGB Input
Interface
MHL-to-HDMI bridges convert an MHL equipped device’s audio and video signals
into a standard HDMI signal. The MHL bridge provides a cost-effective solution
for a docking station or dongle that is fully HDMI compatible.
VastLane SiI9290 MHL-to-HDMI Bridge
Silicon Image: a Market Leader
Silicon Image developed the MHL technology specification and was first-to-market
with MHL products that will have a tremendous impact on the way mobile devices
are used to consume media. MHL technology will allow consumers to enjoy digital
content on large screens - when and where they want - in high definition.
Silicon Image continues to lead the way in innovation and in delivering the most
advanced mobile solutions in HD content. Click the links below to learn more
about VastLane MHL semiconductors or contact a Silicon Image sales
representative to order a starter kit today.
VastLane SiI9226 MHL Transmitter with Parallel RGB Input
Interface
VastLane SiI9290 MHL-to-HDMI Bridge