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DS90UB934-Q1: DS90UB934-Q1 radiation affects surrounding circuits

jeno.zhang
Expert 2885 points
Part Number: DS90UB934-Q1

Tool/software:

Hello，

When using DS90UB934-Q1, the frequency is 456.23MHz, which emits a lot of radiation and affects the surrounding circuits. DS90UB934-Q1 outputs DVP to MS1824, PCLK clock is a 76MHz accessory, which happens to be a multiple of 456. Adding magnetic beads to the DVP circuit reduces radiation by more than 20db. Adding shielding covers near the DS90UB934-Q1 and DVP lines reduces radiation by approximately 8db.

The customer has the following questions, please help answer them. Thanks！

1. Is 76 MHz related to the input rate of LVDS video? For example, 1080p corresponds to 76MHz, and 720p corresponds to other frequencies.

2. 456 MHz should be the transmission rate. If it is the data transmission rate, what determines it? How to calculate? Why is it a 6-fold relationship?

3. Can DS90UB934-Q1 set and adjust any registers or modes to reduce radiation output?

4. Is SSCG modulation effective in reducing radiation？

5. Is it a problem caused by circuit design? Do you have any good suggestions? The PCB diagram is shown below.

  • 0
    TI__Genius 16230 points

    Let me look into this for you. Will reply tomorrow.

  • 0
    TI__Mastermind 24095 points

    Hi Jeno,

    jeno.zhang said:
    1. Is 76 MHz related to the input rate of LVDS video? For example, 1080p corresponds to 76MHz, and 720p corresponds to other frequencies.

    76MHz correlates to the PCLK of the imager data that is being transmitted. The PCLK in this case is calculated by the Horizontal resolution x vertical resolution x frame rate. 

    jeno.zhang said:
    2. 456 MHz should be the transmission rate. If it is the data transmission rate, what determines it? How to calculate? Why is it a 6-fold relationship?

    The transmission line rates are as documented below: 

    The FPD line rate will be determined by the mode of operation. For 76MHz in 10-bit mode, this will be ~1.064Gbps (532MHz). 

    jeno.zhang said:
    3. Can DS90UB934-Q1 set and adjust any registers or modes to reduce radiation output?

    SSCG modulation can be applied to the back channel based on software configuration. 

    Other methods to help improve emission results will be to shift the PCLK frequency depending on where these spikes are being seen. 

    jeno.zhang said:
    4. Is SSCG modulation effective in reducing radiation？

    This can be a useful method however, we would first need to determine where it is coming from. Has testing been done where the back channel was disabled? What testing has been done to determine this is pertaining to the SerDes here? 

    jeno.zhang said:
    5. Is it a problem caused by circuit design? Do you have any good suggestions? The PCB diagram is shown below.

    Can you please share the schematic and layout files for review? For layout, we would like to see the actual project file as this provides better visibility. 

    Best,

    Zoe