How can I build a circuit to generate sine waves? What I am working on is building a 555-timer circuit that gives 50% duty cycle square wave, then using a low-pass or band-pass filter tuned to the frequency of the square wave to get a sine wave from the square wave (because square wave consists of infinite number of sine harmonics).
I haven't tested the circuit in the lab but I've used LTSpice to simulate it and the results was acceptable for low frequency (~72 Hz) but bad for high frequency (~72 kHz). I used this guide from Texas Instruments to build the narrow-band band-pass filter: link. Here is the simulated circuit:
and here is the result for frequency of 72 Hz:
and for 72 kHz:
The output of the 555-timer is a square wave with 50% duty cycle as wanted.
How can I improve this design to get better results?
Are there other ways to generate sine waves with controlled frequency? I don't want ready-made ICs that do this. I want to build a circuit.