ABSTRACT
As described for lowpass fourth-order filters, you can make any filter characteristic with any gain, and it is also still possible to choose a filter characteristic and then choose a gain that makes two of the resistors equal. There are four resistors, and the other two will in general be non-convenient values, though as explained before this is much less of a problem than awkward capacitor values. A fourth-order Butterworth highpass filter is shown in Figure 8.16a, with the exact component values that emerge from the design process.
