Integrated Graphics Display Output; Analog Rgb/Crt; Ramdac/Display Interface - Intel 815 Design Manual

R
8 Integrated Graphics Display
Output
8.1

Analog RGB/CRT

8.1.1

RAMDAC/Display Interface

Figure 49 shows the interface of the RAMDAC analog current outputs with the display. Each DAC
output is doubly terminated with a 75
the board ground and the other termination resistance exists within the display. The equivalent DC
resistance at the output of each DAC output is 37.5 . The current output from each DAC flows
into this equivalent resistive load to produce a video voltage without the need for external
buffering. There is also an LC pi-filter that is used to reduce high-frequency glitches and noise and
to reduce EMI. To maximize performance, the filter impedance, cable impedance, and load
impedance should be the same. The LC pi-filter consists of two 3.3 pF capacitors and a ferrite
bead with a 75
by the RAMDAC while maintaining adequate edge rates to support high-end display resolutions.
®
Intel 815 Chipset Platform Design Guide
resistance. One 75
impedance at 100 MHz. The LC pi-filter is designed to filter glitches produced

Integrated Graphics Display Output

resistance is from the DAC output to
101