WEBENCH® Tools/OPA2140: Active Filter with Attenuation (Gain < 1)

Chi-Yang Hsu

Part Number: OPA2140

Tool/software: WEBENCH® Design Tools

Hi,

I'm using Filter Design Tool to design an active low-pass filter which is also the ADC driver. The gain should be 0.25 to accommodate ADC's input range. However, I found that the smallest allowable gain is 1 in Filter Design Tool.

Is it possible to design an active filter with attenuation (Gain < 1)? If yes, how? If no, why?

Thanks.

over 4 years ago

0 Michael Steffes over 4 years ago

Guru 48395 points

Of course it is possible - Webench is based on the old BurrBrown Filterpro which did not support gain <1,

Thinking low pass here -

1. Sallen key filters min op amp gain is 1,but an attenuating SKF can be done using a divider for that 1st R.

2. MFB filters can easily be made attenuating -little more attention to phase margin necessary

I have my MFB design tool open most of the time for other things, If you need a LP design that can use an MFB what are your targets? On that MFB design topic, I did just recently publish the min GBP solution flow I use here, if you click on the figures, they will enlarge in this one.

https://www.planetanalog.com/use-true-gain-bandwidth-product-to-estimate-required-margin-in-active-filters-insight-13/\

For your design, if a low pass, can you answer -

Fo =

Q =

Gain = 0.25

Single stage or muliple stages?

0 Tamara M Alani over 4 years ago

TI__Genius 10850 points

Hi Chi-Yang,

Thank you for your post. Michael is correct.

Closing this thread now.

-Tamara

Amplifiers

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WEBENCH® Tools/OPA2140: Active Filter with Attenuation (Gain < 1)