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Band Pass Filter Integrated Circuit

Other Parts Discussed in Thread: UAF42, MF10-N, TINA-TI

We need to know if there exist any TI off the shelf Band-pass filter integrated circuit (IC) for IEPE sensors.

Currently, we have designed the Band-pass filter circuit using cascaded Low-pass filter (LPF) and High-pass filter (HPF) circuit. we used dual channel operational amplifier IC with external resistors and capacitors to implement LPF and HPF.

But we need smart solution for it. I hope you can understand our scenario and can help us.

  • Hi Ahmer,

    what do you mean by smart?

    Why not using a DSP?

    Kai

  • Hi Kai,

    thanks for your immediate response.

    Smart means we need any off the shelf filter IC to reduce hardware and make it simple.

  • Hi Ahmer,

    the UAF42 comes into my mind. It's a state-variable filter, already containing precise 1000pF capacitors.

    Kai

  • Hello Ahmer,

    If you can tell us your bandpass filter requirements such as center frequency, bandwidth, gain, order and response type (Butterworth, Bessel, etc.) we might be able to provide you with a more concise filter option. Kai mentions the UAF42. It usually requires a few external resistors to set up the filter as needed. Additionally, there is the MF10-N switched capacitor filter which can be resistor programmed for a specific response. However, when I check the TI stock on the latter device I find no stock so it may not be a good option.

    You may find that the conventional op amp active, LP and HP filter sections you are using are really a good option when it comes to cost, component availability and cost.

    Regards, Thomas

    Precision Amplifiers Applications Engineering 

  • Hello Thomas,

    I am grateful for your detailed response.

    let me mention that we need to filter and amplify the output of IEPE sensor and the bandpass frequency ranges from 0.3Hz to 40KHz.

    The filter could be of second order with response type Butterworth or any other.

    We will appreciate if you also guide us about the best filter option for IEPE sensor.

    Best Regards,

    Ahmer

  • Hi Ahmer,

    I aggree with Thomas. Using a conventional OPAmp circuit may be the smartest option.

    By the way, a high pass filter with a corner frequncy of 0.3Hz would result in a huge time constant. For a second order filter you would need two capacitors in the 100nF range, resistors in the MOhm range assumed:

    So, in order to reduce the neccessary hardware, do you really need second order filters? And do you really need accurate corner frequencies?

    Kai

  • Hi Kai,

    I appreciate your response.

    Actually the filter order is not constraint for us but we require accurate corner frequencies.

    Regards,

    Ahmer

  • Hi Ahmer,

    you could do it this way, with a suited buffer (voltage follower) at the output:

    ahmer_band.TSC

    We need some details of your sensor circuit: What is the source impedance? What is the signal amplitude? What is the supply voltage of sensor? Is a DC offset voltage superimposed to the sensor signal? What supply voltages are available for the buffer? How should the buffered signal look like (amplification, DC offset, etc.)? What will be connected to the output buffer?

    Kai

  • Hello Ahmer,

    I tend to think that cascaded low-pass and high-pass switched capacitor filter sections might provide one the simplest and highly versatile bandpass implementations. I had mentioned TI's MF10-N as a possibility, and there is a TI Applications Report describing the various ways it can be applied to obtain the different filter responses. The minimum component configuration requires only two external resistors and no precision external capacitors required. Any of the classical filter response types such as Butterworth, Chebyshev, Bessel and Cauer can be implemented. You can find the TI report here:

    https://www.ti.com/lit/an/snoa572c/snoa572c.pdf

    You mentioned "We will appreciate if you also guide us about the best filter option for IEPE sensor." The filter frequency requirements will depend on which portions of the 0.3 Hz to 40 kHz range is of interest for the particular IEPE application. It does appear that such filters typically use a flat passband characteristic which suggests a Butterworth response is preferred.

    Regards, Thomas

    Precision Applications Engineering

  • Hi Kai,

    Thank you for elaborate response.

    I am collecting information about the details of filter circuit from my team and soon will let you know all the parameters of our circuit.

    Could you please guide about the tool which you are using in the above screenshot for filter design?

    Regards,

    Ahmer

  • Hello Thomas,

    I have gone through the TI's report and it shows that MF10-N also requires programmable clock generator which ultimately adds software requirement and also increase components count in our design.

    We will prefer that our design should remain simple with cost effective and readily available components.

    In the last message, I liked your suggestion of using conventional LP and HP filters which will have low cost and easily available components.

    I appreciate that you mentioned Butterworth response is preferred for flat passband which is our case.

    Regards,

    Ahmer

  • Hi Ahmer,

    Then, that really leaves the other two options mentioned so far; the discrete op amp active filter and the UAF42. Do have a look at the UAF42 pricing on the TI product page and see if applying two of them meets your cost objective. Secondly, if the UAF42 is applied as a high-pass filter having a lower cutoff of a fraction of a Hertz it is probable that the internal capacitors will have to be paralleled with larger capacitance capacitors. This increases the component count and puts the number of external on par with a conventional RC, op amp active filter stage. 

    Regards, Thomas

    Precision Amplifiers Applications Engineering