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HPF

Category: Software
Product Number: AD8220
Software Version: No

Hello,

I would like to create a HPF (High Pass Filter) with AOP AD8220 but with this wizard It's impossible for me to select this AOP : 

   

Do you know if It's important or finally it's doesn't matter ? I select this AOP (after receiving advice, to have minimum offset, AOP for instrumentation). The simulation look like good :

 

 

But I can't see the magnitude only (just fo check).  

Thank you for your helps. 

     



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[edited by: 206_RC at 12:39 PM (GMT -4) on 21 Jul 2022]
  • Hello,

    Finally this component not suitable for my application, for a small signal 1µV, this AOP this amplifier doesn't do the job.

      

    Do you know a component with a gain of 1 that I can use as HPF (Type Sallen & Key).

    Regards
     

  • Hi,

    I'm trying another component AD8421 with Ibias 500pA and  25µV offset, I'll have always the same problem, I can't detect a small signal with 1µV. Normally this component is better than AD8428, and this component can detect a 1µV input. I don't understand why, I certainly made mistakes in the electronic assembly. 

     

     

    Regards

     

  • Hi,

    I have moved this question about AD8220 to the Instrumentation Amplifier community.  Someone here should be able to assist you.

    Regards and thanks,

    Mae

  • Hi,

    I'll look into this and will get back to you.

    Kristine

  • Hi Kristine, 

    I come back to you about the HPF, if you can't find high pass filters that accept 1µV input in this case I can use after an AOP (about 1mV).
    On the other hand, a filter which has the possibility of adjusting the offset at the output. I think  I come back to my first AOP AD8220 with the following cutoff frequencies : 10/50/100/500/1000 Hz.  

    Thank you for your helps 

    Regards

  • Hi Kristine,

    After severals simulation with different resistor values for the different cutoff frequencies and that I guess this is valid from one amplifier to another. So i think the AOP AD8220 has a very small offset and the output signal is correct.

    For example for cutoff frequency at 1 kHz I have :

    I have the same capacitor values ​​but the resistors change according to the desired cutoff frequency. You can find in this attached my simulation. 

    Thank for your advice 

    AD8220.asc

    Regards

  • Hi,

    After the DS the gain range is between 1 and 1000

    But How can I get a gain of 1 ? With this formula it's impossible :

      

    If Rg is great for exemple 1Gohms, I approach gain 1 but the opposite is happening :

     

    Something is wrong do you have any idea where it could come from ?
    Thank for your answer

    Regards

  • Hi,

    For the G=1 setting, AD8220 is by default set at G=1. You can leave the pin floating and your circuit should be set to G=1.

    I'll get back to you on the HPF.

    Regards,

    Kristine

  • Hello Kristine, 

    After modify to have a Gain of 1, I don't get the expected results. For example with another AOP LT6233 (just to get the values ​​of the components then after I can use theses values on the AD8220).

     

     

    At 100 Hz,

     

    at 100 Hz the filter cuts this frequency well but at a higher frequency we must have a Gain of 1. After this simulation I don't have the same result :

     

    I'll have about 217 mV 

    Thus Gain = 20 Log (Vs/Ve) = 20 Log (217 mV/440 mV) = -6 dB. But after the 'Analog Filter Wizard' Theoretically we should have a gain of 0 dB.

    So something is wrong with this AOP 8220, Do you have any idea about this problem ?

    When I do the simulation with the LT6233 :

    I don't have any problems.

    Thank you for your helps

    Regards.

    Yann DO 

  • Hi Yann DO,

    Apologies if my response took long. Let me answer few questions above.

    Finally this component not suitable for my application, for a small signal 1µV, this AOP this amplifier doesn't do the job.

    Yes, AD8220 won't be the most fit InAmp for your design. AD8220's offset voltage itself is quite high. Please see table below. I've tried increasing the input voltage to at least 1mV and the output became what is expected. AD8220 won't be able to process the 1uV input as its internal offset is larger. You will only see noise.

    I believe LT6233 and AD8220 is not directly comparable in terms of its specs and architecture. Did you have computation for the RC values(how you came up with the values) that you have aside from the analog filter wizard?

    Also please see my simulation below.

    @1kHz cutoff

    @10Hz cutoff

    I used a 1mV input signal (since 1uV wont work), G=1, HPF @ 1kHz/10Hz. I also just used a typical RC filter at the output of the amplifier. Its -3dB is also at 1KHz. It seems like the simulation model is working properly on my side. Would this circuit work for you?

    Could you also share your application? It would also help if you can share a block diagram of your intended design with complete design/circuit requirements. Knowing these details could help us identify a more suited amplifier for your design. 

    Hope this helps!

    Kristine