I have seen this circuit on internet. I would like to understand what its purpose is.
It seems to be related to something which is call "jitter." I have done some research about "jitter" and I think that I have understood what it is. However I do not understand the circuit below and particulary how it works with its double feedbacks (positive and negative.)
In order to get this Relaxation Oscillator or any for that matter, is to have both inputs Vin+- to have the same swing and average voltage for a 50% square wave.
This means if the output swing is. 2 to 13V for BJT type OA or 0 to 15 V for a CMOS then the Vref. Input must be Vcc/2 and not 15V as shown. Then you get 50% duty cycle. Any change in this offset changes the duty cycle.
The Voltage divider Vout to Vin+ thus determines the swing from this average voltage. What is shown is 3.3/(3.3+1) or about 3/4 full swing exponential triangle. Now the CMOS Schmitt Inverter OSC uses a hysteresis of 2/3 full square swing for the triangle..
Then with +/- 1/3 swing same as the 2/3 hysteresis, the ramp is fairly linear but instead of 64% it is 66% but depends on tolerances with slight exponential response T=RC for f~ 1/2T. Reducing the hysteresis increases the frequency just like changing the RC value.
