What is the output frequency variation of RC Oscillator?

[BiDoU]

RC Oscillator

I read on the net that a RC Oscillator can have variations of 5% to 50% of nominal output frequency.

It's true or it happens only if temperature changes of something like that ?

And, if the RC Oscillator can change about 50% of the supposed frequency, it's not a good choice if I want use interruption in my program ?

 

[flatulent]

Re: RC Oscillator

It all depends upon the type of oscillator. If it is an analog feedback type oscillator, the frequency will change with the component values. If you use 1% resistors and NPO capacitors it can be quite stable. If it is a transistor multivibrator, the switching threshold voltage and current sources and power supply voltage will add further variations with temperature.

 

[eternal_nan]

RC Oscillator

I am not aware of the existance of RC oscillator. Perhaps you mean LC oscillator? The free-running oscillation frequency will vary widely with temperature, this is why there is usually a feedback loop around the oscillator that forces it to oscillate at the desired frequency. This is known as a PLL (phase locked loop).

 

[VVV]

Re: RC Oscillator

It depends on the RC oscillator and the components used to build it.
Yes, temperature variations cause the frequency to change, but that is because some parameters of the components change: values of resistors and capacitors, leakage currents of capacitors and transitors and so on. Supply voltage and humidity are factors, too.

But the actual changes can be smaller than the phrase "5% to 50%" suggests. Because everything has to be characterized over a certain range of operating conditions. If the oscillator has to function only from 0°C to +40°C, the change in frequency will be smaller than if the range is -40°C to +125°C.

I do not know what the interruption in program does, so I cannot tell if you can use the RC oscillator or not. If you are referring to the internal RC oscillator of a microcontroller, then you can do anything you want. The frequency of the oscillator will not affect the functionality of the program, only the execution time and the timing of the pulses it generates, if any. So, if you use the program to generate any sort of timing, you need to take into account the accuracy of the oscillator and decide if it's satisfactory for the puspose.

 

[BiDoU]

Re: RC Oscillator

Thank you very much.

I need to generate a delay about 10 seconds. But I don't need precision... But of course I don't want that the delay of about 10 seconds become 20 seconds... And I have to check the state of some push button with an interruption timer (check about 50 times in a second).

But I think that I cannot use RC Oscillator to use a baudrate generator for a UART?