Chrontel CH7219 Nota aplikacyjna - Strona 8

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CHRONTEL

2.7.3

Length Matching for Differential Pairs

The HDMI 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.

Where T

is defined as the reciprocal of Data Transfer Rate and T

bit

Therefore, T

is 10 times T

Pixels

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.

2.7.4

ESD Protection for HDMI Interface

In order to minimize the hazard of ESD, a set of protection diodes are highly recommended for each 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.

System level ESD testing to International standard EN 61000-4-2:1995 / IEC 1000-4-2:1995 has confirmed that the

proper implementation of Chrontel recommended diode protection circuitry, using SEMTECH Rclamp0524P diode

array devices, will protect the CH7219 device from HDMI transmitter discharges of greater than 19kV (contact) and

20kV (air). The Rclamp0524P have a typical capacitance of only 0.30pF between I/O pins. This low capacitance

won't bring too much bad effect on HDMI eye diagram test.

Figure 10 show the connection of HDMI connectors, including the recommended design of Rclamp0524P diode

array devices. HDMI connector is used to connect the CH7219 HDMI outputs.

Table 2: Maximum Skews for the HDMI Transmitter

Skew Type

Intra-Pair Skew

Inter-Pair Skew

. In other words, the intra-pair length matching is much more stringent than the inter-

bit

Maximum at Transmitter

0.15 T

bit

0.20 T

Pixel

is defined as the reciprocal of Clock Rate.

Pixel

206-1000-058

AN-B058

Rev. 0.1

2023-10-25