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AMC1035: Anti-Aliasing Filter Design

Brian Wang0928
Genius 14760 points

Part Number: AMC1035

Could you help to check if this design values of the anti-aliasing filter with resistor divider is ok or not? the cutoff frequency now is designed with 6.6MHz. 

MCE pin connecting to GND. CLK frequency is 20Mhz. what is the sample rate inside the device?

  • 0
    TI__Mastermind 22950 points

    Hi Brian,

    The sample rate of the device is equal to 20MHz (Fclkin). That being said, we generally recommend the cutoff frequency at ~1/2 the modulator rate. So the filter you have with a cutoff frequency of 6.6MHz is a good starting point. Note that the resistor and capacitor values can always be switched out to achieve a different cutoff frequency if necessary. 

    Regards,
    Aaron Estrada

  • 0 in reply to Aaron Estrada
    Prodigy 50 points

    Dear Aaron:

    Is there exists any loading effect risk for these resistors' design? 

    we use resistors for divider 8.25k & 1.8k and anti-aliasing use about 1kohm，

    we afraid that this anti-aliasing filter will make our voltage divider not as precise as we initially designed. 

  • 0 in reply to Leo Chen
    TI__Mastermind 22950 points

    Hi Leo,

    This should not be an issue due to the 1.6Gohm differential input impedance that the AMC1035 has. There will be negligible error due to the low input current on the inputs to the AMC. I ran a quick simulation to show the your system with a high input impedance vs a low input impedance. You can see that  there is a greater error in the system with a low input impedance and the system with high input impedance, the error is < 0.01%

    I hope this helps!

    Regards,
    Aaron Estrada

  • 0 in reply to Aaron Estrada
    Prodigy 50 points

    Dear Aadron:

    Thanks for your explanation, The DC signal seems to not worry about it. 

    However, we will use it to sense the current signal. This waveform will be like 600Hz fundermental and 20KHz triangle wave on it. 

    We need to sense this 20kHz triangle waveform. We need to consider both the R and C values of an anti-aliasing filter to ensure the loading effect.

     Is that correct? 

  • 0 in reply to Leo Chen
    TI__Mastermind 22950 points

    Hi Leo,

    The RC filter has a cutoff frequency well beyond the input signal frequency which is good. As mentioned above, because the input impedance of the AMC1035 is  ~1Gohm, there will be extremely little current flowing to the inputs of the device. This provides a very relaxed constraint on the value of R3 and Rfilter in your schematic. 


    Regards,

    Aaron Estrada