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Reducing Noise on an I2C bus line



  • Hello Lily Lin,

    Can you repost your question in English?

  • Dear,

             Thank you for your reply!

    The question as follows,

    How can use some filters or some other ways to clean the stationary noise in the I2C link(SDA/SCL)?

    The stationary noise is between 30KHz and 100KHz,  appeared per 3Khz step and 5Khz step, and it is about 300mv to 600mv.

  • Hello Lily,

    Since your noise is coming from an external source, there are only 2 ways to make the noise "smaller" relative to the I2C signal.

    1) Increase the I2C bus voltage where you are seeing the voltage. Your noise will stay constant (~300-600 mV), but you can increase your bus voltage to something higher so that the 600 mV won't trigger an accidental high input.

    2) Add capacitance to the I2C bus where you are seeing noise to help reduce the noise magnitude. Keep in mind that the I2C bus cannot have more than 400 pF (include all devices on the bus!). If you add some capacitance (probably 150 pF to 200 pF to start) and then decrease your pull-up resistance to drive the increased capacitance. By doing this, the increased capacaitance on the bus will reduce the noise.

    Of course, the 3rd option is to move the I2C lines away from your source of switching noise to reduce it.
  • Dear,

             Ok! About the first way, I have some questions,

    You said increase the voltage of I2C means increase the transmitted datas voltage? In my opinoin,  I2C is just the supporter to keep the datas between host device and slave ones. 

  • Hello Lily,
    I think what Jonathan is saying that the scale of the noise amplitude compared to the total voltage scale of Vdd is reduced, making the noise a lower percentage of the total voltage swing seen on the lines.

    Do you have waveforms we could look at or more information about your pcb and harness? It sounds like you have noise coupling problems. If you know the source of the noise and how it is coupling then you can try and reduce the noise by changing layout or use filtering.
    -Francis Houde
  • Dear,

             Very very sorry for my so late reply.

              I know the noise source, and I have no tested noise pictutes now.

              In fact,  the trobled problem is that, LCD has some noise signals disturb the TP normal performance. And both TP and LCD have no many useful ideals to solve it. So I think whether I can try the I2C lines to clear the datas TP got.