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TINA/Spice/FILTERPRO: TINA/Spice/FILTERPRO

ln ye
Prodigy 235 points

Part Number: FILTERPRO

Tool/software: TINA-TI or Spice Models

HI :

   I used"filterpro" to design a high pass filter,  i choosed the "Mutiple Feedback ftilter", then i used TINA to simulation, and i found the result is  related to the source resistor, and then i verify the result on the board, i want to ask how can i solve the problem？ can you provide a good method?  by the way , the op-amp is "ADA4841"

   thanks for your reply!

  • 0
    TI__Genius 9775 points

    If i understand your question: basically you're asking why your high pass response changes with the source resistance.. am I correct?

    This is because we're assuming source resistance = 0 ohms as the voltage generator stimulus. To be able do this, you have to drive the high pass circuit with low impedance source. For instance, on simulation you can insert VCVS in between the voltage generator and the HPF circuit as to isolate the impact of your source resisance:

    Voltage Generator + VCVS (Gain of 1x) + HPF Active Cricuit.

    In real life/board/lab measurement, you can replace VCVS (Gain of 1x) with opamp at unity gain configuration.

  • 0 in reply to Herman Theodorus
    Prodigy 235 points

    thanks for you reply!

    yes,you are correct.

    following your method, i do the exercise.

    and i have some questions as follows:

    1.i use the ADA4841 with unity gain configruarion to simulation. if i configured the resource resistor "1MEG ohms", the transfer function is the state of attenuation.

    2. some opamp with unity gain configuration easily  selfly excitate, if i concerned the low noise and low consumption, can you give me a recommendation about the unit gain opamp.

    thank you again!

  • 0 in reply to Herman Theodorus
    Prodigy 235 points

    this afternoon, i used the ADA4841-2 to do the test,one opamp in ADA4841-2 is used for the unity gain configuration, and the other is uesd for high pass filter, the amplitude of the source is 760mv with DC voltage is 1V,

    the two exercise "1.the frequency  is 500Hz,  and 2. the frequency  is 3KHz, the results are as  follows：

    i want to ask the reason of the result ，thank You！

    500Hz

    Output of the unity gain opamp

     

    Output of the high pass fiter

      

     3KHZ

    Output of the unity gain opamp

     

    Output of the high pass fiter

     

     

     

    The schematic

     

  • 0 in reply to Herman Theodorus
    Prodigy 235 points
    thank you ! please see my new problem!
  • 0 in reply to ln ye
    TI__Genius 9775 points
    What's the f-3dB of HPF you're trying to design?

    Also, can you attach your .TSC file or TINA file into this post so that I can take a look what's happening?
  • 0 in reply to Herman Theodorus
    TI__Genius 9775 points
    Hi In ye,

    Jut want to follow up with you on this. Let us know if you still need our help on this. If you do, could you please answer the question I posted last week so that I can further help you.

    If I don't hear from you within a week, I will assume that you somehow have already resolved this issue, and I will be closing this post.

    Herman
  • 0 in reply to Herman Theodorus
    Prodigy 235 points

    unitgain+MFB HPF.TSCi'm so sorry for the delay because of the vacation in recent time.

    f-3dB of HPF is 1HZ.

  • 0 in reply to Herman Theodorus
    Prodigy 235 points

    hi：

    can you give me more suggestion about the problem,thank you!

  • 0 in reply to ln ye
    TI__Genius 9775 points

    Hi,

    I am still looking into this. I am not 100% sure yet why it gives such result.

    Herman

  • 0 in reply to Herman Theodorus
    Prodigy 235 points

    hi herman：

    thank you, actually, the simulation result can also show the problem!

  • 0 in reply to ln ye
    TI__Genius 9775 points
    Hi In ye,

    I noticed that if you sweep the frequency response / bode plot beyond 10kHz and up to 1MHz, you'll notice there is high resonant around 65kHz. I think that's what's causing it.

    I would recommend not to use Multiple-Feedback (MFB) Architecture rather use Sallen-Key (SK) Architecture instead. I think MFB is pretty sensitive to resonant as the feedback components (Resistors and Capacitors) interact with the output impedance of an amplifier.

    Also as far as TI part, you can use OPA836.

    You can also go to www.ti.com/.../products.html to search for the opamps that meet your requirements.

    Herman
  • 0 in reply to ln ye
    TI__Genius 9775 points
    Hi In ye,

    I noticed that if you sweep the frequency response / bode plot beyond 10kHz and up to 1MHz, you'll notice there is high resonant around 65kHz. I think that's what's causing it.

    I would recommend not to use Multiple-Feedback (MFB) Architecture rather use Sallen-Key (SK) Architecture instead. I think MFB is pretty sensitive to resonant as the feedback components (Resistors and Capacitors) interact with the output impedance of an amplifier.

    Also as far as TI part, you can use OPA836.

    You can also go to www.ti.com/.../products.html to search for the opamps that meet your requirements.
  • 0 in reply to ln ye
    TI__Genius 9775 points
    Hi In ye,

    I noticed that if you sweep the frequency response / bode plot beyond 10kHz and up to 1MHz, you'll notice there is high resonant around 65kHz. I think that's what's causing it.

    I would recommend not to use Multiple-Feedback (MFB) Architecture rather use Sallen-Key (SK) Architecture instead. I think MFB is pretty sensitive to resonant as the feedback components (Resistors and Capacitors) interact with the output impedance of an amplifier.

    Also as far as TI part, you can use OPA836.

    You can also go to www.ti.com/.../products.html to search for the opamps that meet your requirements.

    Herman
  • 0 in reply to Herman Theodorus
    Prodigy 235 points

    hi herman：

    thanks for your reply!

    can you tell me how to find the resonant frequency! i have no idea about that !

    i hope to verify whether the schemetic is stable before designing a real board!

  • 0 in reply to ln ye
    TI__Genius 9775 points
    In ye,

    You can follow the following steps:
    1. Open the .TSC or TINA file
    2. Click on Analysis -> AC Analysis -> AC Transfer Characteristic
    3. Alter the end frequency to "10M".
    4. Click "OK".
    5. Observe the graph that comes out of that.
  • 0 in reply to Herman Theodorus
    Prodigy 235 points

    thank you! i will verify another filter type as you said 

  • 0 in reply to ln ye
    TI__Genius 9775 points
    You're welcome. I am going to close this post/thread. If you further questions on the other filter type, please open up a fresh new post with different subject so that we can address it separately on that separate post.