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AMC1305M25: EMI issue in high frequency above 1GHz

xiaoming zhang
Prodigy 10 points
Part Number: AMC1305M25

Tool/software:

hello,

I have several projects failed EMI radiation above 1GHz due to this 1305, do we have some experience or guideline to improved EMI behavior?

the narrow noise is coming from 1305 CLK 20M even without DOUT. I can find noise everywhere by near field scan especially the 1350 is highest

the HV side the AGND is radiated a lot could found this narrow noise higher

and strange thing is the other isolators which close to the 1305 and CLK trace could find higher noise also, more further away more lower. I try to connect AGND and DGND together, it's no obvious change 

I try to add L+C series on the CLK signal no improvement 

the layout shown as below, 15cm CLK and DOUT trace. routing on inner layer, have GND guard ring and complete GND reference.

  • 0
    TI__Expert 5860 points

    Hi Xiaoming,

    Do you have a scope capture of your clock signal.

    xiaoming zhang said:
    I try to add L+C series on the CLK signal no improvement

    How and where did you add these components?  Do you have a schematic and picture you could share?  

    Thanks.

  • 0 in reply to Saleh Ahmad
    Prodigy 10 points

    Hi Ahmad,

    the schematic is like this, the DOUT and CLK connect to MCU directly without other components

    I try to add L and C (10pF) close to the MCU, no improvement

    the normal scope like below

    and after with LC filter on CLK 

  • 0 in reply to xiaoming zhang
    TI__Expert 5860 points

    Hi xiaoming,

    Can you try using an RC filter on the CLK line.  Try keeping the resistor in series near the clk source, and the capacitor to gnd near the device.  Also, it possible to show a picture of how the CLK line is routed, and the GND around it?  What is generating the CLK, and what MCU are you using to read the modulator output (are you using an SDFM module)?

    Thanks.

  • 0 in reply to Saleh Ahmad
    Prodigy 10 points

    Hi Ahmad,

    I put 100R close to CLK source and even with 100p close to device, no obvious improved. I tried everything, it didn't work. I could find noise on all device pin and near filed around.

    the CLK is from the MCU, also read by TC387

    the GND is like below, this is the layer4 signal is shielding by GND, and layer5 is the complete ground reference