This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

THS4531: The design bandwidth of the differential circuit does not match the bandwidth value obtained from simulation.

Part Number: THS4531
Other Parts Discussed in Thread: TINA-TI, THP210


Good day.

   I want to use THS4531 to design a multiple feedback (MFB) low-pass filter (LPF) circuit, in order to amplify the differential signal.

    The MFB LPF circuit is shown in the following figure:


  Now, I have encountered some problems:

     According to theoretical calculations, the transfer function of the filter is 


    and the cutoff frequency fc is 


    Q is 


     Here are the parameters in THS4531 Evaluation Module:

        R1 = 2k ohms;

        R2 = 2k ohms;

        R3 = 255 ohms;

        C2 = 200   pF;

        C1 = 9100   pF;

      Substitute the above parameters into the formula calculation to obtain the cutoff frequency fc:

                                                                                                               fc = 58.986k Hz

      However, I build a simulation model in Tina-Ti, as shown in the following figure:


        Subsequently, the AC transmission characteristics of the circuit were analyzed, and the results are shown in the figure:


           At -3db, the frequency is 6.97k which is not equal to 58.986k Hz.

           My question is why is this happening? Why is the effective bandwidth smaller than what my calculations tell me they should be. I can't find out what I did wrong with my calculations, and I am not sure if there are any other equations to consider.

           Thank you for any helpful answers and suggestions   

           Thank you and stay safe.