In this circuit, a square wave is filtered by a high-order low-pass filter so that a -3-dB frequency will eliminate most harmonics of the waveform. As a result, the filter outputs a fundamental sine wave. This method is applied to generate a sine wave by using a switched- capacitor filter (MAX292) (see the figure). This circuit offers wide frequency range (0.1 Hz to 25 kHz),
low distortion, and constant output amplitude throughout the whole frequency range.