Convert square wave clock signals to low distortion sinewaves:
This circuit derives a pure sinewave from a crystal-controlled clock source by using a ring counter to remove the highest-amplitude unwanted harmonics, and filtering the result with an 8th-order lowpass, switched-capacitor elliptic filter
“low cost” with a $7 filtering chip may be misleading.
I seem to recall playing with much simpler wave shaper / converter circuits out of Mims’ notebooks.This is a cool design and goes beyond the basic designs that I’ve been exposed to from the IC Hobbyist’s handbook & Mims notebooks. Thank you for sharing this!
I’m not an electrical engineer (IANAEE) so maybe its just me, but this design seems very strange. When I see a ring oscillator I think huge temperature drift and jitter. It is possible the circuit produces spectral purity at the expense of overall frequency stability.
This is not a ring oscillator. It is a counter whose output is connected as a crude DAC that produces a rough approximation of a sine wave, which then is cleaned up by a filter.
“square to sine wave converter” is a bit misleading. This converts a high frequency digital clock to an audio frequency sine wave. Basically a DIY DDS frequency synthesizer.
Thanks Evan, yes that actually makes sense. But in that case I don’t see much advantage over one of those analog devices DDS chips or even a cheap micro with a DAC which will get you arbitrary waveforms.