I have wondered for a while in Panasonic is also using column-parallel analog-to-digital conversion in the more video oriented "multi-aspect ratio" sensors of the GH1 and GH2, based mainly on the fact that those sensors do ADC on the sensor, whereas its other 4/3" sensors output an analog signal to off-board ADCs.
EDIT: This is confirmed by the following document and the chipworks link added below END EDIT.
The following document seems to confirm this, at least for a coming sensor if not a current one:http://www.semicon.panasonic.co.jp/en/catalog/cat/pdf/T12013CE.pdf
On page 4 it describes the MN34070, a sensor in "21.9mm optical format" (4/3") of 5054x3518 (about 18MP) with 3.8 micron pixel spacing, and 12-bit column-parallel ADC. That pixel pitch matches the GH2, and the horizontal and vertical pixel counts are only slightly higher than the GH2ís maximums of 4752x3456, which could just be the usual gap between total photosites and output pixel counts.
So my guess is that this is the sensor in the GH2. It could be a new sensor, but having no significant increase in pixel count or resolution would be unusual, as would be describing it in a PR document like this before offering it in a product.
EDIT Confirmed: Chipworks has already disassembled the GH2 and identified its sensor as this MN34070.https://chipworks.secure.force.com/catalog/ProductDetails?sku=PAN-DMC-GH2-K_Pri-Camera&viewState=DetailView&cartID=&g=&parentCategory=&navigationStr=CatalogSearchInc&searchText=ipr