Why output frequency is wandering in RC Oscillator?

[amitbhaiji]

Wander in RC Oscillator.

Hi, I am designing a RC Based oscillator with the ocillation frequency of 1.5Mhz. problem which i am seeing with this circit is that its ouput frequency is wandering by about 150Hz around the center frequency ( Ouptput frequency variation is very slow with respect to time. Can any one suggest me the reason for the same.
and how can i reduce it.

Amit

 

[PaulHolland]

Re: Wander in RC Oscillator.

Hi,

What net frequency are they using in your country ?? if its 60 Hz then the frequency change could be 120 Hz... What R are you using in your RC osc ??..

try to reduce the R if its larger than 50K.. it is possible that your power supply is not clean and that a small signal of 120 Hz is there... try to power your device by batt and see the result .

regards,

Paul.

 

[amitbhaiji]

Re: Wander in RC Oscillator.

oops! Sorry i forget to mention that nearly same wander i am obtaining with my transistor level simulation. So as you predected that the coupling
is not the cause of this drift.
Thsi design is just like the 3 stage ring oscillator with inverter being replaced by the comparator whose other input is from the bandgap refernce source... What i am predicting is " That the upconversion of the flicker noise of bandgap is major contributor towards this drift"
what you feel

Amit

 

[zhaoshibin]

Wander in RC Oscillator.

I have also been puzzled by the OSC design,does anybody have some good material about that?

 

[alexandr22061986]

Re: Wander in RC Oscillator.

For increasing stability you can use instead of RC circuit a quartz resonator that have narrow resonant characteristic

 

[rogerynt]

Re: Wander in RC Oscillator.

Can you show us the the circuit ?