Tektronix DTG5000 Series User Manual

The basic TMDS transmission line is made up of three

data channels and a clock channel. Data consists of

8-bit pixels (256 discrete levels) in each of three

channels (R/G/B). These are encoded into ten-bits

words using 8B/10B encoding to minimize transitions

and to remove the DC component. The signals have

rise times on the order of 100 picoseconds. A pair of

TMDS lines is used when higher data rates are needed.

Figure 1 shows the flow of pixel data from the 

graphics controller or Source device to the digital 

Sink receiver. 

TMDS data rates range from 22.5 megapixels per 

second (Mpps) to 165 Mpps, equivalent to or up to

1.65 G bits per second at the maximum clock rate 

of 165 MHz. The data rate depends on the display

resolution. The relationships of display resolution, bit

rate and clock frequency are shown in the Table 1.

The goal of compliance testing is to ensure interoper-

ability among the many hundreds of different HDMI

devices from as many manufacturers. By conforming

to published HDMI specifications, a device manufacturer

can pave the way for a new product's acceptance in

the marketplace.

Testing should also ensure that the designs are robust

enough to withstand the harsh treatment they can

expect to receive in the real world. As new displays

become more rugged, the devices that use them will

find their way into less sheltered environments than in

the past. Therefore, new devices should be tested to

comply with standards under a variety of operating

conditions, not just “nominal” or best-case conditions.

Test parameters should reach out beyond the basic

limits defined in the specifications. 

Figure 2 illustrates the major elements of the HDMI

transmission system: Source, Cable and Sink. The

Source signals are tested at TP1 while the Sink

devices are tested at TP2. For testing cables, meas-

urements must be performed at both TP1 and TP2.

VGA

640 x 480

252 Mb/s 

25.2 MHz

SVGA

800 x 600

400 Mb/s

40 MHz

XGA

1024 x 768

650 Mb/s

65 MHz

SXGA

1280 x 1024

1080 Mb/s

108 MHz

UXGA

1600 x 1200

1620 Mb/s

162 MHz

640 x 480p

640 x 480

252 Mb/s

25.2 MHz

720 x 480p

720 x 480

270.27 Mb/s

27.027 MHz

576p

768 x 576

270 Mb/s

27 MHz

720p

1280 x 720

742.5 Mb/s

74.25 MHz

1080i

1920 x 1080

742.5 Mb/s

74.25 MHz