groger,
I'd like to attempt to clarify some of the Filter Wizard results, using a simpler design as an illustration. If you still have questions about your specific design, please feel free to follow-up with those questions.
Let's look at the following design in Filter Wizard: a low-pass filter, leaving all of the fields in the "Specifications" tab at their defaults, except changing gain to "40 dB."
Now, looking at the "Stages" drop-down view in the "Component Selection" tab:
Here, you can see the targeted specifications for each stage of your design. So, in this example, we have two stages - Stage A targets a gain of 6.44 V/V, and stage B targets a gain of 15.54 V/V.
Now, take a look at the "Voltage Range" drop down view (still in the "Component Selection" tab):
The "Amplifier Specs" section shows you the datasheet specs for the selected amplifiers (with the voltage supplies you're using - in this example, +/- 5V) - slew rate, max input range, max output range.
Two things to notice:
- The "warning" icons indicate limiting factor in your design, with regards to signal range. In this example design, the output of stage B is maxed out.
- At the top of this view is "Maximum Input Signal Possible:", which is 0.10Vpp in this example design.
So, simply put: Harry is correct. You've set up a circuit with a gain of 100, so assuming you're running on rails of say, +/- 10V, the output of your circuit can never exceed 20Vpp. Which means your circuit won't operate correctly if you drive it with anything larger than approx. 20mVpp.
The specs for staying within the operation range of your circuit is different then the specs in the datasheet that indicate the voltage range that will do irreversible damage to your device. Filter Wizard doesn't report any "smoke point" specs.
As busy as the "Voltage Range" view looks, it gets more busy (and more informative) when you move to the "Component Tolerances" tab.
There is now lots of information about "Worst Case." What is that?
Simply put, Worst Case specifications take into account the variations in your design due to device tolerances. You can adjust the tolerances, but in the example, I'm showing the 5% capacitor, 0.5% resistor, and 20% GBW tolerances. These variations will cause your design to vary in it's intended parameters, including gain, Q, cutoff frequency, etc.
In this example, the gain of the circuit varies pretty significantly due to tolerance:
So, even though the target gain is 40dB, there are variations in the components that could result in 45dB gain (178 V/V).
In the worst case scenario, your output swing on the last stage is still 9.6 Vpp. But, now considering that it's possible that your circuit could have a gain as high as 45dB, you run the risk of overdriving your design if you drive with a input signal any greater than 52 Vpp (9.6 Vpp / 178 = approx 52 Vpp).
If you are still having trouble understanding the Voltage Range information reported by Filter Wizard, start by trying to understand it in the Component Selection tab first. Adding the variation due to tolerances is a very powerful way to see "real world" design issues, but is certainly more information to digest.
I hope this example was helpful in understanding your specific design. Good luck with your filter design!
-Anne