ABSTRACT
Figure 8.2 shows a very familiar circuit-a second-order lowpass Sallen & Key filter with a cutoff (−3 dB) frequency of 1 kHz and a Q of 0.707, giving a maximally flat Butterworth response. The pleasingly simple design equations for cutoff (−3 dB) frequency f0 and Q are given below. Other recognised second-order responses can be designed by taking the Q values from Table 8.1.
