The TFT Connection: Do NVIDIA and ATi Deliver?

DVI Compliance

To test the DVI quality of current graphics cards using ATi and NVIDIA graphics processors, we sent six graphics cards in to the Silicon Image testing labs and had them checked for DVI compliance.

Interestingly, running a test for DVI compliance is not a mandatory requirement for receiving a DVI license. As a result, products reach the market that claim to have DVI capabilities but don't adhere to the specifications. One of the reasons for this is the very complex and therefore costly testing procedure.

As a reaction, Silicon Image founded the DVI Compliance Test Center (CTC) in December of 2003. Manufacturers of DVI capable devices can send in their products and have them tested for DVI compliance. This is exactly what we did with our six graphics cards.

DVI Compliance Tests

DVI compliance tests are divided into three categories: the transmitter (usually a graphics card), the cable and the receiver (monitor). To assess DVI compliance, so-called eye diagrams are created that represent the DVI signal. To pass, the signal has to stay within certain defined borders. If the signals are outside of these limits, the device is not DVI compliant.

This image shows an eye diagram of a TMDS transmitter at 162 MHz (UXGA) with billions of data bits.

The eye diagram test is the most crucial test when verifying the signal quality. The diagrams reveal signal fluctuation (jitter), amplitude and "ringing effects." These tests allow a direct evaluation of a device's DVI quality.

DVI compliance tests exist for:

1. Transmitters: Eye diagram with defined borders
2. Cables: Eye diagrams created before and after the signal is sent over the cable are compared to one another. Again, there are strictly defined limits within which the signal must lie. The eye is smaller than that of the transmitter (more tolerance).
3. Receivers: The test eye in which no signals may lie is once again even smaller.