During IDF (Intel Developer Forum) Fall 2005, which is happening right now in San Francisco, California, Intel presented the final specs for the new CE-ATA hard drive standard, especially the connector format this new standard will use. The images you will see in this article are from CE-ATA presentation on this show.
CE-ATA is a standard for small hard drives targeted to consumer electronics products, such as media players (MP3, video, etc), digital cameras and digital camcorders. Right now the main standard available to this segment is CF+ (Compact Flash), which uses a 50-pin connector. Too many pins for a very small device – consumer electronics products use 1-inch hard drives! Also it uses 5 V signals, while everything else has already moved or is moving to 3.3 V signaling.
CE-ATA connector uses only 10 pins and has only 1/200th the volume of CF+:
- CF+ connector: 1.69 x 1.43 x 0.13 inches (42.8 x 36.4 x 3.3 mm)
- CE-ATA connector: 0.32 x 0.13 x 0.035 inches (8.1 x 3.4 x 0.9 mm)
In Figure 3, you can see a CE-ATA drive from Hitachi, which measures only 1.18 x 1.58 inches (30 mm x 40 mm). Compare it to a quarter, it’s really amazing. Its connector has Washington’s nose to chin distance!
CE-ATA connector has four data pins, and because of that is also called “4x CE-ATA” or “4-bit CE-ATA”. At first engineers tried to use the same connector used by MMC cards, but one problem emerged: crosstalk.
Crosstalk is basically when a signal carried in one wire interferes or even corrupts the signal that is being transmitted in the wire adjacent to it. Physically speaking, this happens because when we have a data being transmitted over a wire, it generates a electromagnetic field around it, and a wire inside this field acts like an antenna, capturing the signal thus modifying the signal that was being originally transmitted in that particular wire.
This is also a very particular problem on CE-ATA drives because both CF+ and MMC standards were originally created to be used by memory cards. As you know, memory cards don’t use a flat-cable to be connected to the host device (card reader): you just plug in the card inside the reader and that’s it. On CE-ATA drives, however, the engineers decided to allow them to use a small flat-cable, allowing better accommodation for the hard drive inside the consumer electronics device. However, this flat-cable helps the antenna-factor problem.
In Figure 4, you can see data being transmitted from a CE-ATA drive to a CE device using the standard MMC connector. The crosstalk was of 375 mV, which is very high.
The solution was to change the position of the signals on the connector. Instead of putting data signals side-by-side, engineers changed that approach and put a voltage or a ground signal between data signals, which are immune to the electromagnetic interference and work as a shield, solving the cross-talk issue.
The result was a crosstalk of only 59.6 mV, as you can see in Figure 6. A crosstalk that low doesn’t interfere on the drive’s communication.