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Original question:

TMDS181: output is unstable with 1080p, 59.94fps

TMDS181: "Unstable" output video for specific video source.

Juraj Pollak
Prodigy 30 points
Part Number: TMDS181
Other Parts Discussed in Thread: SN75DP159, ,

Hello,

We are observing an issue with specific video source 1080p60 (camera) when using SN75DP159 device on sink side.

We can replicate this issue on TMDS181RGZEVM eval board:

Source (camera 1080p60) -> Display // OK

Source (camera 1080p60) - > TMDS181RGZEVM -> Display // Unstable video

When reading TMDS181 registers no evident issue is reported:

 

Only workaround we found so far is to switch TMDS181 to redriver mode. When we force TMDS181 to redriver mode display is showing stable picture.

Please help us to understand why when TMDS181 is in retimer mode the picture is unstable with some specific video sources when passing through TMDS181.

(I would expect that retimer mode should be more robust as it profits from skew compensation and jitter cleaning functions)

Any hints how to tune retimer mode (by PLL settings for example) to be “more stable” please?

 

Thank you.

  • 0
    TI__Guru**** 181321 points

    Hi,

    Can they also try the follow I2C write to the TMDS181 registers? These writes will change the TMDS181 PLL bandwidth

    <aardvark>

    <configure i2c="1" spi="1" gpio="0" tpower="1" pullups="0"/>

    <i2c_bitrate khz="100"/>

    <i2c_write addr="0x5e" count="1" radix="16">09 06</i2c_write> <sleep ms="10"/>   -> Set lane and polarity swap, disable automatically power down base on HDP_SNK

    <i2c_write addr="0x5e" count="1" radix="16">FF 01</i2c_write> <sleep ms="10"/> -> Select Page 1 registers

    <i2c_write addr="0x5e" count="1" radix="16">01 01</i2c_write> <sleep ms="10"/> -> Charge pump enable. PLL mode, used with the HDMI

    <i2c_write addr="0x5e" count="1" radix="16">02 3F</i2c_write> <sleep ms="10"/>  -> Charge pump current control. 7F max charge pump current setting, may need to sweep the value

    <i2c_write addr="0x5e" count="1" radix="16">00 03</i2c_write> <sleep ms="10"/> -> Bit 0 -> Enable PLL and Bit 1 -> Enable bandgap

    <i2c_write addr="0x5e" count="1" radix="16">0B 33</i2c_write> <sleep ms="10"/> -> Bit [1:0] Loop filter resistance, try setting to 30h and 31h

    <i2c_write addr="0x5e" count="1" radix="16">A1 02</i2c_write> <sleep ms="10"/> -> Bit 1 -> Override control for Page 1 register 0x0B, 0x0C, and 0x0D. The register 0x0B write will take effect

    <i2c_write addr="0x5e" count="1" radix="16">A4 03</i2c_write> <sleep ms="10"/> -> Bit 1 -> Page 1 Register 0x01 override control. Bit 0 -> Page 1 Register 0x00 override control

    <i2c_write addr="0x5e" count="1" radix="16">FF 00</i2c_write> <sleep ms="10"/> -> Select Page 0 registers

    </aardvark>

    Thanks

    David

  • 0 in reply to David (ASIC) Liu
    Prodigy 30 points

    Hi David,

    Thanks for your support.

    With new PLL settings, we are detecting an improvement. (By increasing charge pump current, output video is more stable when TMDS181 is in retimer mode). For max. charge pump current (7F), the best results we are observing.

    Remaining Queries:

    1. Can we use this new PLL settings for all supported resolutions (bandwidth) of TMDS181?

                Are there any drawbacks when we “manually” change PLL bandwidth compared to default bandwidth settings?

     

    1. Please help us to understand why when TMDS181 is in retimer mode, output video is unstable with some specific video sources when video is passing through the TMDS181 (with default PLL bandwidth)?

    BTW: As described in the beginning, with redriver mode we are seeing stable video for specific video sources which are unstable in retimer mode.

    Thanks.

  • +1 in reply to Juraj Pollak
    TI__Guru**** 181321 points

    Hi,

    The TMDS181 initial PLL setting was chosen that results in small PLL peaking and a bandwidth setting that can track and filter out the noise of most video sources at that time. When manually changing the PLL bandwidth, the PLL peaking may increase while providing better tracking capability. 

    When TMDS181 is in redriver mode, its PLL is disabled so the jitter from the source gets passed onto the sink and the sink RX may able to track and filter the jitter. But when TMDS181 is in retimer mode, its PLL is enabled and TMDS181 may not properly filter the input jitter with its default bandwidth. With the input jitter not being properly filtered out and also having TMDS181 PLL in the path, the sink RX then may not then able to properly filter out the jitter.

    You can test out the new bandwidth with different resolution and see if there is an issue with the new setting.

    Thanks

    David