about Filter Wizard Design it's limit to 40dB
Is there a way to plan for 80dB or more?
We recommend you use a separate gain stage for >40 dB gain designs (and potentially even for designs with less gain than that.)
For small amounts of gain, it can be useful to incorporate gain into filter stages rather than being forced to add another separate gain stage. However it comes with drawbacks. Incorporating gain into the filter stages:
- puts more requirements on the op amp, likely requiring a faster, less accurate amplifier.
- can increase the effect of component tolerances.
- can make debugging more difficult than analyzing a gain circuit and filter circuit separately
- will likely have higher noise than a design with a high gain stage in front
At some point these drawbacks are big enough that it makes more sense just to add gain separately before the filter.
One thing we thought about was to allow higher gains and then have the filter wizard add a separate stage purely for gain, But the more we thought about it, the less valuable this feature seemed to be. Typically in high gain designs, the high gain stage is the one that interfaces with the sensor. The amplifier's requirements should be set by the sensor, which the filter wizard doesn't know anything about.
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