CHRONTEL AN-B012
10 206-1000-012 Rev1.9, 06/30/2020
2.8 DVI/HDMI Outputs
The TLC, TLC*, TDC [2:0], TDC [2:0]* signals are high frequency differential signals that need to be routed with
special precautions. Since those signals are differential, they must be routed in pairs.
2.8.1 Differential Pair Impedance
To match the external cable impedance and maintain the maximal energy efficiency it is important to meet the
impedance target of 100 Ω±10% for the differential data/clock traces. The restriction of this impedance target is to
prevent any loss of signal strengths resulting from a reflection of unwanted signals. The impedance can be acquired
by proper design of trace length, trace width, signal layer thickness, board dielectric, etc. The DVI/HDMI differential
pairs should be routed on the top layer directly to the DVI/HDMI connector pads if possible.
2.8.2 Trace Routing Length
To prevent from capacitive and impedance loading, trace lengths should be kept as minimal as possible. Vias and
bends should always be minimized; inductive effects may be introduced, causing spikes in the signals. Trace routing
lengths from CH7033B to the HDMI/DVI connector are limited to a maximum of 2 inches. The CH7033B should be
as close to the HDMI/DVI connector as possible.
2.8.3 Length Matching for Differential Pairs
The HDMI/DVI specifies the intra-pair skew and the inter-pair skew as in Table 2. The intra-pair skew is the
maximum allowable time difference on both low-to-high and high-to-low transitions between the true and
complement signals. The inter-pair skew is the maximum allowable time difference on both low-to-high and high-to-
low transitions between any two single-ended data signals that do not constitute a differential pair.
Table 2: Maximum Skews for the HDMI/DVI Transmitter
Where Tbit is defined as the reciprocal of Data Transfer Rate and TPixel is defined as the reciprocal of Clock Rate.
Therefore, TPixel is 10 times Tbit. In other words, the intra-pair length matching is much more stringent than the inter-
pair length matching.
It is recommended that length matching of both signals of a differential pair be within 5 mils. Length matching should
occur on a segment by segment basis. Segments might include the path between vias, resistor pads, capacitor pads, a
pin, an edge-finger pad, or any combinations of them, etc. Length matching from one pair to any other should be
within 100 mils.
Note that lengths should only be counted to the pins or pad edge. Additional etch within the edge-finger pad, for
instance, is electrically considered part of the pad itself.
2.8.4 ESD Protection for HDMI/DVI Interface
In order to minimize the hazardof ESD, a set of protection diodes are highly recommended for each DVI/HDMI
Output (data and clock).
International standard EN 55024:1998 establishes 4kV as the common immunity requirement for contact discharges
in electronic systems. 8kV is also established as the common immunity requirement for air discharges in electronic
systems. International standard EN 61000-4-2:1995 / IEC 1000-4-2:1995 establishes the immunity testing and
measurement techniques.
