Notes on HDMI in TV applications

Notes on HDMI in TV applications

Considerations for HDMI in TV applications
As a new digital video interface specification, HDMI is more and more widely used. There are more and more digital TVs using the HDMI interface. This article explains several details of using HDMI.
Due to the high data transmission speed of HDMI, its wiring has strict requirements.
First, there are several problems in the HDMI layout part, as follows:
1. ESD components: Please do not use STZ6.2N, STZ6.8N (this should be the reason why the impedance is only 50 Ohm after installing the component), it is recommended to use a low capacitance value
BAV99 (<= 1.5pF), or special ESD device for HDMI high-speed signal
2. Differential signal layout please strictly follow the differential principle, and don't make the differential spacing change randomly (as shown below)
3. When using BAV99, please refer to the following diagram for layout:

4. In the case of using ESD (0603), please refer to figure 3 for layout.
5. Because the wiring may cause signal attenuation, it is best to ensure that the signal line width is 24mil
Above, the interval between differential signals can only be 8mil. Insert an 8mil ground wire between one set of differential signals and another set of differential signals, and try to make the four sets of signal lines as long as possible. The signal wiring adopts circular wiring to reduce the impedance of the wiring (between 85 ohms and 115 ohms).
Second, the specific application of HDMI
1. HDMI switch PS201 / PS301 (Parade), TMDS341A (TI) is compatible in application.
2. When debugging HDMI, the KEY of EDID and HDCP must be burned, only a few DVDs
The output HDMI does not need to detect KEY. If there is only EDID, then we can only see the image without sound. In addition, in the face of many manufacturers ’HDMI interface devices, some
The HDMI cable is not in good contact with the socket, and it may cause no signal. The signal of some groups is weak, causing the image to have color dots and the image to jump. Of course HPD testing can provide
The HPD_SINK signal is provided for the master device to judge and use.
3. The reason why the DVD 1080P output is not supported is that there is an error in the HDMI signal packet output by the DVD (it can be read out through the BK0B_05 register), our software has strictly checked the correctness of the packet, so the image cannot be displayed, add a patch, when 1080p When there is an error in the input HDMI packet, the error detection processing program is skipped, and the default is YUV mode, which is forced to display.
The patch is in the attachment, just overwrite the original function.
4. The voltage of V-SCL and V-SDA of DDC is required to be 4.5 to 5.5V
Between high and low. If the CEC standard is used, there is also a level requirement for the CEC pin.

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