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At long last, the use of High-Definition Multimedia Interface (HDMI) in mobile phones, car navigation systems and other products is approaching reality. Molex Inc of the US and other companies have prototyped a miniature HDMI connector (Fig 1) for use in compact portable products such as mobile phones and compact digital cameras. The new “mini connector” has the same 19 pins as the current design, but is only about half the size, or roughly the same as a Micro Universal Serial Bus (USB) connector (Fig 2). It is significantly smaller than the existing Type C HDMI connector for portable equipment.
 Japan Aviation Electronics Industry Ltd of Japan, meanwhile, prototyped an HDMI connector for automotive use, offering improved reliability and durability.
All of these connectors are prototypes based on the next version of the HDMI standard, now being developed. The next official version of the HDMI standard is expected to be released in the first half of 2009, which would mean that the first compliant products could appear as early as the second half of 2009 (Note 1).
Half the Size
 In addition to Molex, mini connectors were also prototyped by Yazaki Corp of Japan (manufacturing by Yazaki Parts Co Ltd of Japan), and a third firm. The connectors were said to have been developed based on the specs for the Type D mini connector slated for inclusion in the next version of the HDMI standard.
The Molex prototype, for example, is only about half the size of the current Type C connector. A comparison of receptacle dimensions shows that the Type D is only 2.8mm high by 6.4mm wide, much smaller than the Type C at 3.2 x 11.2mm (Fig 1). Connector mounting area has been reduced to 45%, and volume by about half.
To ensure backward compatibility in the smaller format, the number of pins is the same 19 as the current Type A and Type C, arranged in two horizontal rows. This decision was made based on total characteristics including connector and cable. The pin layout is essentially the same as the current Type A, and according to a source at Molex Japan Co Ltd of Japan is designed to resist electromagnetic interference.
 It would also have been possible to use a single row of pins, but that would have made the pin pitch extremely small, and increased the possibility of pin shorts if the connector were inserted at an angle (Note 2).
The two-row design made it possible to use a 0.4mm pin pitch horizontally and 0.6mm vertically. Shrinking the connector with the same pin count posed some difficulties in manufacture, but according to Molex Japan it was possible because “We already had experience in manufacturing a connector with two rows and tightly-spaced pins.”
10,000-Cycle Durability
The prototypes are smaller than existing Type C connectors, but deliver equivalent strength and electrical characteristics. They are assured for the same 5,000 insertion cycles as Type C, and in fact there would be “no problem” meeting the 10,000-cycle durability cited for the Micro USB connector, says Molex Japan. An engineer at a leading HDMI company praised electrical characteristics, saying they surpassed the Type C (Fig 3).
 The new, smaller Type D connector is about the same size as the Micro USB, and designers added features to make sure that users didn’t confuse the two when plugging them in. The plug end of the connector is higher than the Micro USB receptacle, and the Type D receptacle is narrower than the Micro USB plug (Fig 2b, c).
EMI Control Challenges
The connector prototyped for automotive applications by Japan Aviation Electronics Industry succeeds in delivering the reliability and durability demanded in automotive systems (Fig 4).
 The prototype is larger than the current Type A connector, but has been made “as small as possible” while still functioning as a high-reliability, high-durability connector for automotive use, says the firm. It also has the same 19 pins, assuring backward compatibility.
One of the biggest problems encountered in developing a connector for automotive use was electromagnetic interference (EMI) generated by the connectors, cables, etc. A developer revealed, “We spent a large portion of total prototype development time on controlling EMI.” Shielding for connectors, cables, etc was improved to suppress spurious radiation (Note 3).
by Tadashi Nezu
Note 1: The prototyped connector is based on a provisional specification, and therefore it is possible that connector specs may change by the time the next version of the HDMI spec is approved.
Note 2: In addition, if a cable with a circular cross-section is used with a long, narrow connector, line lengths will vary between signal lines, causing skew. If the cable cross-section is matched to the shape of the connector, bending in the horizontal direction becomes difficult.
Note 3: The structure is also designed to resist dislodging even when exposed to vibration, as well as suppressing EMI. Connector attachment and assembly have been simplified for automotive applications, while also meeting the wide operating temperature range and long-term reliability demanded.
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