Apple files patent for ‘low EMI capacitive trackpad’
Posted by Dennis Sellers 
Mar 30, 2006 at 7:16pm
On March 30, the US Patent & Trademark Office revealed an Apple patent application titled ‘Low EMI capacitive trackpad,’ originally filed on September 24, 2004.
Patent FIG. 5 (illustrated) shows a computer system incorporating a low EMI capacitive trackpad in accordance with the invention.
Apple’s abstract
A printed circuit board (PCB) assembly provides a two layer capacitive trackpad sensor in which an EMI ground grid is interposed among the sensor’s capacitive elements on each of its layers. The EMI grid on each of the two layers is electrically coupled via, typically, vias. The described arrangement of sensor elements (capacitor plates) and EMI ground grid traces may be incorporated into a PCB having additional layers (e.g., a four, six or eight layer PCB). If used in this manner, additional vias are provided on the PCB which permit electrical coupling between these “additional layers” and which are electrically isolated from, and shielded by, the EMI ground grid.
Details only a geek could love
Referring to FIGS. 3A and 3B, a first embodiment of the invention is shown in which a two layer PCB includes first layer 300 (FIG. 3A) and second layer 350 (FIG. 3B). First layer 300 includes repeated column regions 302-308; void regions 310-322, EMI ground grid regions 324-328 and vias 330-346.
Second layer 350 includes repeated row regions 352-354, isolated plate regions 356-378, EMI ground grid regions 380-384 and vias 386-399. When the vias of layer 300 (330-346) and layer 350 (386-399) are aligned it can be seen that: row regions 352 and 354 align with void regions 310-322; isolated plate regions 356-378 align with column regions 304-308 and layer 300’s EMI ground grid regions 324-328 run substantially orthogonal to layer 350’s EMI ground grid regions 380-384. During fabrication, vias in layer 300 are electrically coupled to their corresponding vias in layer 350 to form an electrically continuous EMI ground grid interposed between (and around) the sensor’s capacitive plates (302-308, 352, 354 and 356-378).
Referring to FIGS. 4A and 4B, a second embodiment of the invention is shown in which a four layer PCB includes first layer 400 (FIG. 4A) and second layer 450 (FIG. 4B) substantially in accord with FIGS. 3A and 3B.
In contrast to the embodiment of FIGS. 3A and 3B, however, additional PCB layers (not shown) are provided and additional vias (402-418 and 452-468) are incorporated into the EMI ground grid (420-424 and 470-474) to permit electrical connectivity between components (e.g., electrical traces and/or devices) in or on the additional PCB layers. It is significant that the additional vias are electrically isolated from the EMI ground grid by annular regions (426-442 and 476-492). This annular (void) region permits the vias to be used to couple traces between the additional PCB layers without interfering with, or being interfered by, the operation of the trackpad sensor. That is, the EMI ground grid acts as a shield to both the trackpad sensor elements and the additional signal vias. One of ordinary skill in the art will recognize that PCBs having more than two layers typically isolate adjacent layers (i.e., formed on the top of a first PCB core and the bottom of a second, adjacent, PCB core) with an insulating material such as, for example, by preimpregnated bonding layer material or “PREPREG.”
Notice
Macsimum News presents only a brief summary of patents with associated graphic(s) for journalistic news purposes as each such patent application and/or grant is revealed by the U.S. Patent & Trade Office. Readers are cautioned that the full text of any patent applications and/or grants should be read in its entirety for further details.
The inventors listed on patent 20060066581 are Benjamin Lyon and Steven P. Hotelling.
neo@macsimumnews.com
Other trackpad patents
System and method for processing raw data of track pad device
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Contributor
Dennis Sellers
Dennis has been a newspaper editor/reporter (seven years) and teacher (seven years). He has over 4,000 magazine, newspaper and online articles to his credit. He has also covered the Mac and tech industries for over a decade for such online publications as MacCentral, MacMinute and now MacsimumNews.
