It is not possible to obtain a perfect pure sine wave by simply filtering a square wave with resistors and capacitors. While filtering can help shape the waveform, it cannot completely transform a square wave into a perfect sine wave.
A square wave consists of a fundamental frequency and its odd harmonics, which are integer multiples of the fundamental frequency. The rapid transitions between high and low levels in a square wave result in a spectrum that includes multiple frequency components.
Filtering a square wave using passive components like resistors and capacitors can attenuate the higher frequency components, but it cannot eliminate them entirely. As a result, the filtered waveform will still retain some harmonic content and will not be a pure sine wave.
To obtain a closer approximation of a sine wave, more sophisticated techniques are required. One common approach is to use an active filter, such as an op-amp-based circuit, or digital signal processing techniques to generate a sine wave approximation. These methods involve more complex circuitry or algorithms to synthesize a waveform that closely resembles a sine wave.
In practical applications where a pure sine wave is necessary, dedicated signal generation devices such as function generators or software-based algorithms are commonly used to produce high-quality sine wave signals. These methods employ techniques specifically designed to generate accurate sine waveforms with minimal harmonic distortion.