X-bit labs

Directly Unified: Nvidia GeForce 8800 Architecture Review (page 8)

Category: Video

by Alexey Stepin , Yaroslav Lyssenko, Anton Shilov

[ 11/09/2006 | 06:34 PM ]

Nvidia GeForce 8800 GTX

PCB Design

Implementing such a complex device as the GeForce 8800 GTX called for a new, original printed-circuit board. Such factors as the high power consumption of the G80 chip, the use of a separate chip containing TMDS transmitters and a RAMDAC, and the 384-bit memory bus all contributed to making the card very large.

In order to give you an understanding of how huge the new graphics card from Nvidia is, take a look at the following photograph:

As you can see, the GeForce 8800 GTX’s PCB is much longer than the Radeon X1900 XTX’s: 27.9cm against 23cm. This must be the reason why the power connectors have been moved from the reverse to the face side of the PCB so that you could plug the cables normally in a cramped system case. The massive cooler covers most of the graphics card with its components, so we had to unfasten 11 large spring-loaded screws and 8 smaller screws to remove it. Here’s the new card in all its nudity:

A large part of the PCB – over one third of it – is occupied by power circuitry that is capable of powering the 681-million-transistor chip and has power consumption comparable to that of today’s top-end CPUs. Nvidia has always been meticulous about powering its top-end graphics cards, and the GeForce 8800 GTX is not an exception. You computer must be equipped with a 450W or higher power supply that can yield a combined current of no less than 30A on its 12V power rail (in other words, each of the PSU’s “virtual” 12V output lines must sustain a load of at least 15A without triggering off the overcurrent protection). Both PCI Express power connectors must be attached to the card. If you don’t do that, it either won’t start up, emitting a loud warning signal, or will start up at reduced frequencies, depending on the connector attached.

In the bottom right corner there’s an ordinary piezo-speaker that is responsible for sending the warning signal and a 4-pin connector for the cooler’s fan. A little above them you can see a seat for a 6-pin connector which probably serves some engineering purposes.

A PWM controller Primarion PX3540 is the heart of the power circuit. It is located on the reverse side of the PCB.

The rest of the PCB, around the GPU and memory chips, looks oddly simple and unexciting except for the small FCBGA-packaged chip with an open die that is marked as NVIO-1-A3.

Nvidia didn’t make the G80 chip even more complex by integrating TMDS transmitters and a RAMDAC into it. These units used to be integrated into the GPU, but now they all reside in a separate special-purpose chip.