THP210: Active 2nd order Elliptic filter design for Audio application

Hello Narendra,

You stated in your other e2e post "I need to design a 2nd order differential active Elliptic filter for the sharp attenuation of -40dB/decade in stop bands and passband is 100Hz to 20KHz and one more filter with the pass band of 300Hz to 6KHz."

Here are my thoughts on an approach to fulfill the filter requirements:

1. Since you require differential-in, differential-out filter the THP210, or OPA1637 FDA op amps are well suited for this audio application.
2. I do not know of any Elliptic filter topology for an FDA. The Multiple Feedback (MFB) is commonly applied. See my article in the TI AAJ, "Using the infinite-gain, MFB filter topology in fully differential active filters." https://www.ti.com/lit/an/slyt337/slyt337.pdf
3. 300 Hz to 6 kHz is a wide bandwidth to cover with a bandpass filter stage. Since 6 kHz is 20x 300 Hz a better approach may be to cascade a 2nd-order 6 kHz low-pass, with a second-order 300 Hz high-pass. Each 2nd-order section will provide a 40 dB/decade roll-off.
4. Each filter section can be synthesized using one of the filter synthesis programs such as TI's Filter Designer Tool: https://www.ti.com/design-resources/design-tools-simulation/filter-designer.html
5. In general, a Chebyshev response will provide the next sharpest cutoff at the edges of the passband after an Elliptic response. You can set the passband ripple that your application can tolerate.

Regards, Thomas

Precision Amplifiers Applications Engineering

Hi Thomas i already  cascaded Chebyshev MFB  two stages with low &high-pass sections but attenuation cannot be achieved with out allowing more ripple in the pass pand but in my application ripple should not cross 0.5dB ,since i need -40dB/decade as roll off in stop band i tried to tune the filter but i am getting peak overshoot at pole frequency. I read your application note slyt337 i am unable to find anything related to attenuation, passband ripple, damping, quality factor even in filter design tool also there is not enough resources to modify the capacitor and resistor values or changing the Damping factors.

Narendra,

Is this the same filter as your post here?

THP210: Getting peak over shoot in the filter frequency response - Amplifiers forum - Amplifiers - TI E2E support forums

If so, I'd like to end this thread and just keep the focus on the thread above.

Thanks,
Mike